Less Than 1% of Core-collapse Supernovae in the Local Universe Occur in Elliptical
Galaxies
I. Irani1 , S. J. Prentice2 , S. Schulze1,3 , A. Gal-Yam1 , Jacob Teffs4, Paolo Mazzali4,5 , J. Sollerman6 , E. P. Gonzalez7,8,
K. Taggart9 , Kishalay De10 , Christoffer Fremling11 , Daniel A. Perley4 , Nora L. Strotjohann1 , Mansi M. Kasliwal11 ,
A. Howell7,8, S. Dhawan3,12 , Anastasios Tzanidakis10 , Daichi Hiramatsu7,8 , Erik C. Kool6 , J. P. Anderson13 ,
T. E. Müller-Bravo14 , Richard Dekany15 , Mariusz Gromadzki16 , Roberta Carini17 , L. Galbany18 , Andrew J. Drake11,
Jamison Burke7,8 , Craig Pellegrino7,8 , Massimo Della Valle19,20,21 , Michael S. Medford22,23 , Ben Rusholme24 ,
D. R. Young25 , Claudia P. Gutiérrez26,27 , Cosimo Inserra28 , Rafia Omer29, David L. Shupe24 , T.-W. Chen6,
Kyung Min Shin30 , Ofer Yaron1 , Curtis McCully7 , Matt Nicholl31 , and Reed Riddle15
1 Department of Particle Physics and Astrophysics, Weizmann Institute of Science, 234 Herzl St., 7610001 Rehovot, Israel; idoirani@gmail.com
2 School of Physics, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
3 Department of Physics, The Oskar Klein Center, Stockholm University, AlbaNova, SE-10691 Stockholm, Sweden
4 Astrophysics Research Institute, Liverpool John Moores University, IC2 Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF, UK
5Max-Planck Institut fur Astrophysik, Karl-Schwarzschild-Str. 1, D-85741 Garching, Germany
6 Department of Astronomy, The Oskar Klein Center, Stockholm University, AlbaNova, SE-10691 Stockholm, Sweden
7 Las Cumbres Observatory, 6740 Cortona Dr., Suite 102, Goleta, CA, 93117, USA
8 Department of Physics, University of California, Santa Barbara, Santa Barbara, CA, 93106, USA
9 Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA
10 Cahill Center for Astrophysics, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA
11 Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
12 Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
13 European Southern Observatory, Alonso de Córdova 3107, Casilla 19, Santiago, Chile
14 School of Physics and Astronomy, University of Southampton, Southampton, Hampshire, SO17 1BJ, UK
15 Caltech Optical Observatories, California Institute of Technology, Pasadena, CA 91125, USA
16 Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
17 INAF-Osservatorio Astronomico di Roma, Via Frascati 33, I-00040 Monte Porzio Catone (RM), Italy
18 Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans, s/n, E-08193 Barcelona, Spain
19 INAF-Capodimonte Astronomical Observatory, Salita Moiariello 16, 80131 Naples, Italy
20 INFN Naples, Naples I-80126, Italy
21 ICRANet, Piazza della Repubblica 10, I-65122 Pescara, Italy
22 Department of Astronomy, University of California, Berkeley, Berkeley, CA 94720, USA
23 Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., Berkeley, CA 94720, USA
24 IPAC, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA
25 Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast BT7 1NN, UK
26 Finnish Centre for Astronomy with ESO (FINCA), FI-20014 University of Turku, Finland
27 Tuorla Observatory, Department of Physics and Astronomy, FI-20014 University of Turku, Finland
28 School of Physics & Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff, CF24 3AA, UK
29 School of Physics and Astronomy, University of Minnesota, 116 Church St. SE, Minneapolis MN 55455, USA
30 California Institute of Technology, Pasadena, CA 91125, USA
31 Birmingham Institute for Gravitational Wave Astronomy and School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK
Received 2021 October 5; revised 2021 December 12; accepted 2021 December 13; published 2022 March 2
Abstract
We present observations of three core-collapse supernovae (CCSNe) in elliptical hosts, detected by the Zwicky
Transient Facility Bright Transient Survey (BTS). SN 2019ape is a SN Ic that exploded in the main body of a typical
elliptical galaxy. Its properties are consistent with an explosion of a regular SN Ic progenitor. A secondary g-band
light-curve peak could indicate interaction of the ejecta with circumstellar material (CSM). An Hα-emitting source at
the explosion site suggests a residual local star formation origin. SN 2018fsh and SN 2020uik are SNe II which
exploded in the outskirts of elliptical galaxies. SN 2020uik shows typical spectra for SNe II, while SN 2018fsh shows a
boxy nebular Hα profile, a signature of CSM interaction. We combine these 3 SNe with 7 events from the literature
and analyze their hosts as a sample. We present multi-wavelength photometry of the hosts, and compare this to
archival photometry of all BTS hosts. Using the spectroscopically complete BTS, we conclude that -+0.3% 0.10.3 of all
CCSNe occur in elliptical galaxies. We derive star formation rates and stellar masses for the host galaxies and compare
them to the properties of other SN hosts. We show that CCSNe in ellipticals have larger physical separations from their
hosts compared to SNe Ia in elliptical galaxies, and discuss implications for star-forming activity in elliptical galaxies.
Unified Astronomy Thesaurus concepts: Core-collapse supernovae (304); Early-type galaxies (429); Star
formation (1569)
Supporting material: machine-readable table
The Astrophysical Journal, 927:10 (22pp), 2022 March 1 https://doi.org/10.3847/1538-4357/ac4709
© 2022. The Author(s). Published by the American Astronomical Society.
Original content from this work may be used under the terms
of the Creative Commons Attribution 4.0 licence. Any further
distribution of this work must maintain attribution to the author(s) and the title
of the work, journal citation and DOI.
1
1. Introduction
Core-collapse supernovae (CCSNe) are widely considered to
be the terminal explosion of massive (>8Me) stars. Except for
SNe Ia and Ca-Rich SNe Ib, which are likely thermonuclear
explosions of white dwarf stars, all other major SN types are
currently thought to have a massive star origin (Gal-Yam 2017
and references therein). Specifically, all hydrogen-rich SNe
(SNe II), hydrogen-poor and silicon-poor SNe (SNe Ib/c and
SNe Ibn), and superluminous SNe (SLSN) are thought to have
a massive star origin. The progenitors of most SNe II are
thought to be red supergiants (RSG), as confirmed by direct
progenitor detections in deep pre-explosion images (for
reviews, see Smartt 2015; Van Dyk 2017 and references
therein). The progenitors of SNe Ic have not yet been solidly
detected (Eldridge et al. 2013; Smartt 2015, but c.f. Van Dyk
et al. 2018). They are thought to be either massive, single
Wolf–Rayet (WR) stars (e.g., Taddia et al. 2019), or massive
stars whose hydrogen-rich envelope has been stripped in a
binary interaction (Eldridge et al. 2013). As expected, SNe Ic
have been found exclusively in star-forming environments.
Similarly, other CCSN types are rarely found outside of such
environments (e.g., Hakobyan et al. 2012). Suh et al. (2011)
investigated previous claims of CCSNe in early-type (i.e.,
elliptical and lenticular) host galaxies, but found that these were
either the result of an erroneous SN classification, or that the
host galaxies had a systematically bluer ultraviolet (UV)—
optical color than the early-type hosts of SNe Ia
(NUV− rPS1∼ 3 mag compared to NUV− rPS1∼ 5.4 mag,
respectively). Recently, Sedgwick et al. (2021) reported 36
CCSNe occurring in elliptical galaxies from a sample of 421
photometrically classified CCSNe from the SDSS-II Supernova
Survey (Sako et al. 2018) and argue that elliptical galaxies
account for ∼11% of the cosmic star formation budget. Kaviraj
(2014) estimated, based on the Sloan Digital Sky Survey
(SDSS; York et al. 2000) stripe 82 data, that the contribution of
early-type galaxies to the cosmic star formation budget is 14%.
A few cases of CCSNe in the outskirts of non-star-forming
elliptical galaxies have been reported. SN 2016hil was a SN II
found at a relatively large offset of 26 kpc from the center of a
massive elliptical galaxy (Irani et al. 2019). The SN Ibn PS1-
12sk was found at a similar offset from a massive elliptical
galaxy (Sanders et al. 2013). In both cases, the large offset from
the massive nearby elliptical galaxy might indicate that the
association is spurious, although deep observations of the SN
site using the Hubble Space Telescope (HST) and Keck argue
against an underlying faint host galaxy (Hosseinzadeh et al.
2019; Irani et al. 2019).
Hubble first classified galaxies using a “tuning fork” scheme
(Hubble 1926), using the presence of spiral and bar features. This
scheme was later improved (e.g., by de Vaucouleurs 1959;
Sandage 1961) to include finer morphological features. Galaxy
morphology is broadly categorized into bulge-dominated “red
and dead” early-type galaxies and blue star-forming late-type
galaxies. While the colors, morphologies, and star formation of
galaxies are tightly correlated, they do not map exactly onto each
other (Trager et al. 2000; Strateva et al. 2001; De Lucia et al.
2006; Buta 2011). The observed bimodality in galaxy colors and
star formation properties requires a physical mechanism to
quench star formation in massive evolved galaxies; a topic of
ongoing research (e.g., Gabor et al. 2010; Man & Belli 2018).
While generally considered passive galaxies, the low-level star
formation still ongoing in some early-type galaxies is a topic of
ongoing research. Kaviraj et al. (2008) found that up to ∼30% of
early-type galaxies might have undergone recent episodes of star
formation, leading to bluer UV–optical colors. Hernández &
Bruzual (2009) further suggest that the blue colors of early-type
galaxies with 4<NUV− rPS1< 5.4 mag could be explained by
a recent low-level star-forming episode or by the presence of
extreme horizontal branch (EHB) stars. Petty et al. (2013) also
suggested EHB stars are the source of the blue UV–optical colors
of UV excess early-type galaxies. Salim et al. (2012) studied a
sample of early-type galaxies from the SDSS survey with a
strong UV excess and found structured UV morphology in 93%
of their sample. In 75% of the cases, the star formation extended
to offsets of 25–75 kpc, indicative of galaxy-scale inside-out
growth, fueled by accretion of gas from the intergalactic medium
(IGM). Such growth is found to occur for massive galaxies
(Sánchez-Blázquez et al. 2007; Pérez et al. 2013). The rest of
their sample is characterized by patchy and centered (5–15 kpc)
star formation. By contrast, Gomes et al. (2016) found star-
forming lanes in 3 nearby early-type galaxies, documenting the
still ongoing star formation in these galaxies. Assuming the
ongoing star formation in elliptical galaxies is similar to star
formation in spirals, a population of SNe is expected to explode
in these environments.
New transient surveys such as the Zwicky Transient Facility
(ZTF; Bellm et al. 2019; Graham et al. 2019; Dekany et al. 2020),
the Asteroid Terrestrial Last Alert System (ATLAS; Tonry et al.
2018), the Panoramic Survey Telescope and Rapid Response
System 1 (PS1; Chambers et al. 2016), and the All Sky
Automated Survey for Supernovae (ASAS-SN; Shappee et al.
2014), monitor the entire night sky with a high cadence and to
unprecedented depths and discover thousands of SNe in the
process. This allows SNe to be used as probes to trace star
formation in elliptical galaxies where star formation was thought
to have ceased. The ZTF Bright Transient Survey (BTS; Fremling
et al. 2020; Perley et al. 2020) is the largest untargeted
spectroscopically complete SN survey to date. It classifies 93%
of all SNe with peak magnitudes mpeak< 18.5mag and 75% of all
SNe with mpeak< 19mag. This sample allows for a systematic
study of residual CCSN populations in low-redshift environments.
In this paper, we used the BTS to conduct a search for
spectroscopically confirmed CCSNe in elliptical host galaxies.
We present observations of three such SNe. We combine these
events with a sample of literature objects, analyze the SN
properties, and characterize their host environments. This paper is
organized as follows. In Section 2 we describe our sample
selection and the comparison samples. In Section 3 we present the
spectroscopic and photometric observations of the SNe and their
hosts. In Section 4 we characterize the transients and their host
galaxies. We discuss the implications of these results and present
our conclusions in Section 5. Throughout this paper we assume
H0= 73 km s
−1Mpc−1 and a ΛCDM cosmology with Ωm= 0.27
and ΩΛ= 0.73 (Wilkinson Microwave Anisotropy Probe 3 yr
results; Spergel et al. 2007). All magnitudes are reported in the
AB system and are corrected for line-of-sight reddening based on
Schlafly & Finkbeiner (2011); see Section 2.5.
2. Sample
2.1. Candidate Selection Process
As of 2020 December 30, the BTS sample contains 4018
spectroscopically classified SNe. Of these, we select SNe
satisfying the following criteria:
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The Astrophysical Journal, 927:10 (22pp), 2022 March 1 Irani et al.
1. The redshift is 0.015< z< 0.1. The lower bound is meant
to avoid shredding of nearby galaxies into multiple
sources in galaxy catalogs and the upper bound is due to
the reduced completeness of galaxy redshift catalogs
(Fremling et al. 2020), required to ensure the SN and the
galaxy are indeed associated.
2. The likely host galaxies of the ZTF BTS SNe are
continuously identified in the BTS sample explorer32
(Perley et al. 2020). This is done by an automatic cross
matching of the SN positions with the nearest galaxies in
the Pan-STARRS (PS1; Chambers et al. 2016) or SDSS
(Alam et al. 2015) photometric catalogs. Host-galaxy
matching is complete out to an offset of <90″ and
<30 kpc (projected distance) and employs a criterion to
distinguish between multiple host-galaxy associations.
We only select SNe that are associated with a host galaxy
in this way.
Of the 4018 SNe in the sample, 3855 had a redshift in the
required range. Among those, we could identify the most likely
host galaxy of 3330 SNe. We cross match these host galaxies
with the Galaxy Evolution Explorer (GALEX) Data Release
(DR) 8/9 (Martin et al. 2005) and the ALLWISE (Cutri et al.
2021) catalogs and obtain the FUV (1542Å), NUV (2274Å)
and W1–W4 [33,500Å–220,000Å] IR photometry. We correct
the results for Galactic reddening using the maps of Schlafly
& Finkbeiner (2011). Queries were performed from the VizieR
Catalog (Ochsenbein et al. 2000) using astroquery
(Ginsburg 2019). We use the host photometry to define a
sample of CCSNe with early-type hosts. These are defined
here as:
1. Galaxies with W2−W3< 0.5 mag and NUV− rPS1>
3 mag, if both the W2−W3 color and the NUV− rPS1
colors are available.
2. Or galaxies with W2−W3< 0.3, if only the W2−W3
color is available.
This definition is satisfied by 75% of elliptical galaxies in the
Galaxy Zoo (Lintott et al. 2011) sample. It is chosen so that it
includes all regions in the color–color parameter space that
have a higher number of ellipticals compared to spirals,
calculated in 0.5 mag bins.
Next, we search for any SN not classified as an SN Ia, and
examine the host morphology visually. To be considered a
CCSN in an elliptical host, we require:
1. Independent and consistent spectroscopic redshift mea-
surements of both the SN and the host galaxy from
publicly available catalogs.
2. Visual confirmation of the red color and absence of a bar,
spiral arms, or a disk structure in the deepest available
images.
3. Once aperture-matched photometry and source deble-
nding is performed, the host galaxy still occupies our
double-color region for elliptical galaxies.
4. Confirmation of a CCSN classification: SN classifications
in the BTS (Fremling et al. 2020) are made using both
human inspection and using SuperNova IDentifi-
cation (SNID; Blondin & Tonry 2007), and are thus
generally reliable. However, since CCSNe generally
avoid elliptical galaxies, we take special care to avoid
misclassified SNe Ia and require verification of the SN
type through a visual inspection of the spectrum and by
fitting the spectra using a python adaptation of Superfit
(Howell et al. 2005) with an updated spectrum template
bank (S. Goldwasser et al., in preparation).
Twenty-one CCSNe pass our color criteria, of which only 4
SN hosts emerged as having elliptical morphology—
SN 2020uik (SN II), SN 2018fsh (SN II), SN 2019ape (SN
Ic) and SN 2019cmv (SLSN-II). While SN 2019cmv passes our
sample criteria, we exclude it due to the combination of having
a high offset from the nearby elliptical galaxy, and the shallow
limits on an underlying host at the SN site. At the distance of
SN 2019cmv, we cannot rule out the presence of a faint,
underlying host with a brightness of³14 mag. Such low-mass
hosts have been observed for several SLSNe (Perley et al.
2016; Schulze et al. 2018), and are the most likely explanation
for the unusual location of SN 2019cmv. SN 2020oce,
classified as a SN Ic in the BTS, also passes our sample
criteria, but we find that it is fit well by spectra of 91bg-like
SNe Ia, and so exclude it from our sample. In Figure 1 we show
PS1 image cutouts of the three CCSN host galaxies from the
BTS matching our criteria. The images are constructed using
the method described in Lupton et al. (2004).
The data points in the left panel of Figure 2 show the UV–
optical and mid-infrared (MIR) colors of CCSN hosts
compared to the colors of elliptical and spiral galaxies from
the Galaxy Zoo catalog (Lintott et al. 2011). In this plot, a good
separation is achieved between the colors of elliptical and spiral
galaxies. In the right panel of Figure 2 we show the same
color–color plot for the host galaxies of SNe Ia. As expected,
the vast majority of CCSNe occur in the region occupied by
Figure 1. The host galaxies of (from left to right) SN 2018fsh, SN 2019ape, and SN 2020uik, constructed from PS1 stacks in the gri bands. The location of the SN is
marked with white crosshairs. The angular scale is provided in the lower left corner of each panel.
32 https://sites.astro.caltech.edu/ztf/bts/explorer.php
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The Astrophysical Journal, 927:10 (22pp), 2022 March 1 Irani et al.
spirals. In Figure 3 we show the mean observed colors of
spirals and ellipticals from the Galaxy Zoo catalog normalized
to the W2 band and compare them with the colors of elliptical
host galaxies of CCSNe. As this figure shows, the most
significant difference between the spectral energy distribution
(SED) of spiral and elliptical galaxies is seen in the UV and in
the MIR. The elliptical host galaxies of CCSNe have SEDs
similar to galaxy zoo ellipticals.
2.2. Literature Sample
In addition to the objects presented in this paper, we compile
a sample of CCSNe in elliptical galaxies from the literature. We
apply the criteria in Section 2.1 to the CCSN sample (Schulze
et al. 2021) from the Palomar Transient Factory (PTF; Law
et al. 2009) and the intermediate Palomar Transient Factory
(iPTF; Kulkarni 2013), and to published CCSNe from Suh
et al. (2011), Hakobyan et al. (2008), Graham et al. (2012), and
Sanders et al. (2013). Our findings generally agree with the
conclusions of these papers—that most CCSNe near elliptical
galaxies occurred in either misclassified spirals or star-forming
ellipticals. A small minority of the SNe analyzed in these
papers do pass our criteria, and we combine these with our BTS
objects to form a combined sample. We further require that
objects in our sample have public spectra, so that the
classification can be confirmed. In total, our combined sample
includes 10 SNe, listed in Table 1, along with their
classifications and estimated peak luminosities. We note that
the host of the Type II SN Abell 399 11 19 0 (Graham et al.
2012) did not pass our sample inclusion criteria since it is not
detected in both the NUV and W3 bands. However, the
available limits (W2−W3< 0.06 mag, NUV− rPS1> 4.5
mag), along with the galaxy morphology, indicate this host is
also an elliptical galaxy.
2.3. Comparison Samples
Throughout this work, we use several SN and galaxy
samples for comparison. These are:
1. BTS CCSNe: we selected all BTS SNe classified as
CCSNe that occurred in host galaxies with measured
WISE W2−W3 and UV–optical colors. This sample
consists of 478 objects, of which 465 fall outside of the
region that we associate with elliptical galaxies in
Figure 2.
2. SNe Ia elliptical galaxies: we selected all BTS SNe
(Perley et al. 2020) classified as SNe Ia that occurred in
host galaxies with both W2−W3< 0.5 mag and
NUV− rPS1> 3 mag. This sample contains 240 objects.
3. Galaxy Zoo (Lintott et al. 2011) galaxies: we randomly
selected 50,000 galaxies from the Galaxy Zoo sample that
have morphological classifications and with a redshift in
the range 0.015< z< 0.05. Of these galaxies, 1309
(10265) were classified as elliptical (spiral). Queries were
performed using CasJobs (OMullane et al. 2005). We
Figure 2. Left: color–color diagram for all CCSNe hosts with full color information. Each data point represents the colors of the host galaxy of an SN. The black
dashed lines indicate the region defining our color criterion for elliptical galaxies. SNe whose hosts passed our criteria as elliptical galaxies are marked with a yellow
star (this work) or a blue star (literature sample), using the host photometry reported in this work. All BTS CCSN hosts are marked with dots color-coded based on the
SN type as indicated in the legend. The red and blue shaded regions are the 2d smoothed distributions of Galaxy Zoo ellipticals and spirals. These also appear as a 1D
color kernel density estimate on the top and right panels. Right: similar to the previous plot, but for the hosts of SNe Ia.
Figure 3. The observed host colors relative to the W2 band for Galaxy Zoo
spirals (cyan) and Galaxy Zoo ellipticals (pink). CCSN host galaxies that
passed our criteria as true elliptical galaxies are marked with a yellow star (this
work) or a blue star (literature sample). The error bars represent the standard
deviation of the Galaxy Zoo sample or the measurement error for
individual SNe.
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The Astrophysical Journal, 927:10 (22pp), 2022 March 1 Irani et al.
note that Lintott et al. (2011) use a broad categorization
of galaxies into ellipticals and spirals. The elliptical group
includes both elliptical (E) and lenticular (S0) galaxies.
2.4. SN Discovery and Classification
2.4.1. SN 2018fsh
SN 2018fsh was detected in the ZTF alert stream on UT
2018 August 31.52 (JD 2458362.02) at J2000 coordinates of
α= 08h30m56 6, d = +  ¢ 39 50 09. 2 at a brightness of r= 19.0
mag (Fremling 2018). Based on a spectrum obtained on UT
2018 September 17.56 (JD 2458379.06) the transient was
classified as a SN II (Fremling et al. 2018) at a redshift of
z= 0.029. This redshift is consistent with the value
(z= 0.029084) listed in the NASA Extragalactic Database
(NED)33 for MCG +07-18-013, a red galaxy offset by 38 6
from the SN location. The host redshift corresponds to a
distance of 122± 9Mpc corrected for Virgo, Shapley, and
Great attractor infall (Mould et al. 2000, via NED). ZTF did not
observe the field in the three months before the first SN
detection and the last ZTF nondetection is on 2018 May 25.17.
The SN is visible in data by ATLAS as early as UT 2018 June
15.26, ∼84 days before the first ZTF detection and 4 days after
the previous nondetection. We adopt UT 2018 June 13.25 (JD
2458282.75), the midpoint between the last nondetection and
the first detection, as an estimate of the explosion time for this
event.
2.4.2. SN 2019ape
SN 2019ape was detected in Pan-STARRS1 data on UT
2019 Feb. 05.39 (JD 2458519.89) at J2000 coordinates of
α= 10h51m42 5, d = +  ¢ 18 28 52. 73 at a brightness of w=
18.57 mag (Chambers et al. 2019). On UT 2019 February
08.71 (JD 2458523.21) the transient was classified as a SN Ic
(Carini et al. 2019) at a redshift of z= 0.02 based on the SN
features. De et al. (2020) acquired a nebular spectrum of the SN
300 days after explosion and conclude that it does not belong to
the Ca-rich group based on the Ca II to [O I] ratio. SN 2019ape
was detected in the massive elliptical NGC 3426
(z= 0.020414). We adopt the host redshift and a corresponding
redshift-dependent distance of 90.4± 6.4 Mpc corrected for
Virgo, Shapley, and Great attractor infall. Applying the ZTF
forced-photometry pipeline (Masci et al. 2018) yields an earlier
detection from UT 2019 January 31.44 (JD 2458514.94), at a
brightness of r= 20.52± 0.19 mag. The latest nondetection is
at>20.9 mag 3 days earlier. We estimate the explosion date as
JD 2458513.44±1.5, the midpoint between the first detection
and the last nondetection.
2.4.3. SN 2020uik
SN 2020uik was detected in ATLAS data on UT 2020 Sep.
20.62 (JD 2459113.12) at J2000 coordinates of α=
08h01m54 18,d = -  ¢ 06 45 39. 52 at a brightness of c=
18.5 mag (Tonry et al. 2020). On UT 2020 October 18.53
(JD 2459141.03) the transient was classified as a SN II
(Dahiwale & Fremling 2020) at a redshift of z= 0.03 based on
the SN features. These are consistent with the NED redshift of
z= 0.028156 of WISEA J080154.84-064527.1, a red galaxy
offset by 15 0 from the SN location. We adopt the host redshift
and a corresponding redshift-dependent distance of 118.1±
8.3Mpc corrected for Virgo, Shapley, and Great attractor infall.
SN 2020uik was detected during a plateau in its light curve
after a long period in which the field was not observed.
Assuming a plateau that extends 100 days since explosion
(Arcavi et al. 2017), we estimate an explosion time of around
JD 2459085, 28 days prior to the first detection. The best-fitting
Superfit template of its first spectrum, taken 56 days after the
estimated explosion, is the spectrum of the SN II SN 2013fs
(taken 57 days after explosion; Yaron et al. 2017).
2.5. Extinction
We queried the NASA/IPAC NED Galactic Extinction
Calculator34 for the foreground Galactic extinction in the line
of sight toward each of the 3 SNe presented in this work,
derived from the maps of Schlafly & Finkbeiner (2011). We
find a line-of-sight extinction of E(B−V,MW)= 0.043 mag for
SN 2018fsh E(B−V,MW)= 0.031 mag for SN 2019ape and
E(B−V,MW)= 0.082 mag for SN 2020uik. We estimate the host
extinction of SN 2019ape (along the line of sight to the SN)
using the g− r color curve of SN 2019ape compared to
intrinsic color curves of SNe Ic (Stritzinger et al. 2018; Drout
et al. 2011). We find E(B−V,Host)= 0.14± 0.03 mag. This value
Table 1
Sample of CCSNe with Elliptical Hosts Analyzed in This Work
SN R.A. (J2000) Decl. (J2000) Redshift Projected Offset (kpc) Peak Mr (AB mag)
a,b SN Type Reference
SN2003ky 179.52625 47.33319 0.047 8.3 −19.3 II Armstrong (2003)
SN2006ee 29.8975 14.00544 0.015 4.3 −16.64 II Puckett et al. (2006)
SN2006gy 49.36275 41.40542 0.019 1.1 −20.2 IIn Ofek et al. (2007); Smith et al. (2007)
PTF10gqf 225.96897 55.62717 0.045 29.0 −16.5 II Schulze et al. (2021)
PS1-12sk 131.22858 42.97136 0.054 32.9 −19.2 Ibn Sanders et al. (2013)
SN2016hil 17.603106 14.204318 0.061 26.4 −17.0 II Irani et al. (2019)
PTF16pq 139.39429 18.95197 0.028 4.0 −16.1 II Schulze et al. (2021)
SN2018fsh 127.73595 39.83588 0.029 22.8 −18.2 II This work
SN2019ape 162.92728 18.4813 0.020 4.8 −16.83 Ic This work
SN2020uik 120.47579 −6.76099 0.028 8.6 −17.22 II This work
Notes.
a All measurements are taken from the Open Supernova Catalog (Guillochon et al. 2017) or from cited references.
b Observed r-band magnitudes were adopted when available. Otherwise, an average between R and V bands was adopted. If no color information was available, we
adopt the peak magnitude in the observed band. Magnitudes were corrected for Galactic reddening.
33 https://ned.ipac.caltech.edu/ 34 https://ned.ipac.caltech.edu/forms/calculator.html
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The Astrophysical Journal, 927:10 (22pp), 2022 March 1 Irani et al.
is broadly consistent with the value derived using the
equivalent width of the Na D doublet absorption feature
(Poznanski et al. 2012). We do not attempt to estimate the host
extinction for SN 2018fsh or SN 2020uik, but estimate these
are not significant due to the large offset from their host
galaxies.
3. Observations
3.1. Photometry
For all SNe discussed in this paper, we acquired gri
photometry using the P48 ZTF camera (Dekany et al. 2020).
These data were processed using the ZTF data-processing
system (Masci et al. 2018). Light curves were obtained using
the forced-photometry pipeline (Masci et al. 2018) on
difference images produced using the optimal image subtrac-
tion algorithm of Zackay et al. (2016) at the position of the SN,
as reported by the first ZTF alert. We report detections above a
3σ threshold. Same-night detections were binned in order to
boost the signal. Additional photometry was acquired with:
1. The Las Cumbres Observatory (LCO) network of 1 m
telescopes through the Global Supernova Project
(Howell 2019). Photometric data were reduced using
the lcogtsnpipe pipeline which performs PSF-fitting
photometry. Landolt standard field stars were used to
calculate the zero-points for the filters UBV, whereas for
gri bands we use Sloan magnitudes of stars in the same
field as the object.
2. The two ATLAS 0.5 m telescopes on Haleakala and
Mauna Loa, Hawaii, USA (Tonry et al. 2018). Data were
reduced using the forced-photometry service (Smith et al.
2020).
3. The 2.0 m robotic Liverpool Telescope (LT; Steele et al.
2004) at the Observatorio del Roque de los Muchachos
Observatory on La Palma using the optical imager (IO:O)
through the g, r, i, and z bands. Photometry was reduced
using standard IRAF routines within a custom PYTHON
script and stacked using SWarp (Bertin et al. 2002).
Digital image subtraction was performed versus PS1
reference imaging following the techniques of Fremling
et al. (2016) and calibration was performed relative to
PS1 photometric standards.
4. The Rainbow Camera (Blagorodnova et al. 2018) on the
Palomar 60 inch telescope (P60; Cenko et al. 2006).
Reductions were performed using the automatic pipeline
described by Fremling et al. (2016).
For SN 2019ape, instrument cross calibration was performed
by applying constant shifts calculated using polynomial fits to
band-specific light curves. In case a single instrument was
available for a given band, the calibration was performed using
synthetic photometry on the spectra scaled to r-band photo-
metry to ensure accuracy relative to other bands. Following
these procedures, a constant shift of −0.32 mag was applied to
LCO g-band light curves to match the evolution of LT and ZTF
light curves. No other offsets were required. The photometry in
this work will be made available through the Weizmann
Interactive Supernova data REPository (WISeREP;Yaron &
Gal-Yam 2012) upon publication, and is provided in Table 2.
The light curves of SN 2018fsh and SN 2020uik are shown in
Figure 4, and the light curves of SN 2019ape are shown in
Figure 5.
3.2. Spectroscopy
Spectroscopic follow-up of SNe appearing in this work was
performed using a variety of instruments:
1. The 3.6 m ESO New Technology Telescope (NTT) at La
Silla, Chile, using the ESO Faint Object Spectrograph and
Camera (v.2) (EFOSC2; Buzzoni et al. 1984) as part of
ePESSTO+. These data were reduced using the PESSTO
pipeline (Smartt et al. 2015).
2. The Nordic Optical telescope (NOT) using The Alhambra
Faint Object Spectrograph and Camera (ALFOSC).
Reductions were performed using FOSCGUI.35
3. The 200 inch Hale telescope at Palomar observatory
using the Double Beam Spectrograph (Oke &
Gunn 1982). These data were reduced following standard
procedures using the P200/DBSP pipeline described in
Bellm & Sesar (2016).
4. The Spectral Energy Distribution machine (SEDm;
Blagorodnova et al. 2018) mounted on the Palomar 60
inch telescope. Data were reduced using the automatic
SEDm pipeline (Rigault et al. 2019).
5. The Spectrograph for the Rapid Acquisition of Transients
(SPRAT; Piascik et al. 2014) on the Liverpool Telescope.
SPRAT spectra were reduced using the LT pipeline
(Smith et al. 2016) and flux calibrated using a custom
PYTHON routine.
6. The Low Resolution Imaging Spectrometer (LRIS; Oke
et al. 1995) on the 10-m Keck I telescope. The data were
reduced using the LRIS automated reduction
pipeline (LPipe; Perley 2019).
Figure 6 shows the spectrum of SN 2018fsh 96 days after
explosion in comparison with the best-fitting SN II spectrum at
a similar phase using Superfit. Figures 7 and 8 show the
spectral evolution of SN 2019ape and SN 2020uik, respec-
tively. Table 3 contains a log of spectroscopic observations
presented in this work. All spectra will be made available to the
public on WISeREP36 upon publication.
3.3. Host-galaxy Photometry
We retrieved archival images of all SN host galaxies
discussed in this work from Galaxy Evolution Explorer
(GALEX) Data Release (DR) 8/9 (Martin et al. 2005), SDSS
DR9 (Ahn et al. 2012), PS1 DR1 (Chambers et al. 2016), the
Two-Micron All Sky Survey (2MASS; Skrutskie et al. 2006),
and the unWISE (Lang 2014) images from the NEOWISE
(Meisner et al. 2017) Reactivation Year 3. For SNe included in
our sample we use the matched-aperture photometry software
package Lambda Adaptive Multi-Band Deblending
Algorithm in R (LAMBDAR; Wright et al. 2016) that is
based on a photometry software package developed by Bourne
et al. (2012) and the tools presented by Schulze et al. (2021).
The photometry was either calibrated against zero-points
(GALEX, PS1, SDSS, and NEOWISE) or against a set of
stars (2MASS). We correct the measurements for Milky Way
extinction based on Schlafly & Finkbeiner (2011). The
resulting photometry is summarized in Tables 4 and 5. We
note that in the case of SN 2016hil, the W3 measurements are
estimated from the W2−W3 color reported in
35 http://graspa.oapd.inaf.it/foscgui.html
36 https://www.wiserep.org/
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The Astrophysical Journal, 927:10 (22pp), 2022 March 1 Irani et al.
Irani et al. (2019), where MIR photometry is measured from
ALLWISE data using the same methodology described here.
4. Results
In this section we analyze the properties of the three newly
discovered SNe. In Section 4.1 we discuss the light curve,
spectra, and location of the SNe II SN 2018fsh and
SN 2020uik. In Section 4.2 we analyze our observations of
SN 2019ape. We argue it is a typical SN Ic by comparing it to
other SNe Ic, and by modeling its spectroscopic evolution. We
present evidence that the SN has formed near the explosion site
and is a result of low-level star formation in its elliptical host.
In Section 4.3 we derive host galaxy properties for the
combined sample of CCSNe in ellipticals and compare them to
the hosts of all BTS SNe (CCSNe and SNe Ia). We discuss
these results and their implications for star formation in
elliptical galaxies in Section 5.
Table 2
Photometric Observations of SN 2018fsh, SN 2019ape, and SN 2020uik
SN Name JD Estimated Time from Explosion (Rest-frame Days) Instrument Filter AB Magnitude
SN 2019ape 2458514.94 1.47 ZTF r 20.45 ± 0.19
SN 2019ape 2458522.92 9.29 ZTF g 18.72 ± 0.01
SN 2019ape 2458524.45 10.79 LT g 18.63 ± 0.01
SN 2019ape 2458524.45 10.79 LT r 18.07 ± 0.01
SN 2019ape 2458524.45 10.79 LT z 18.14 ± 0.02
SN 2019ape 2458524.45 10.79 LT i 18.19 ± 0.01
SN 2019ape 2458526.93 13.22 ZTF g 18.67 ± 0.03
SN 2019ape 2458528.0 14.27 LT g 18.63 ± 0.01
SN 2018fsh 2458284.76 4.63 ATLAS c 17.14 ± 0.03
SN 2018fsh 2458286.76 6.57 ATLAS o 17.22 ± 0.09
SN 2018fsh 2458371.01 88.44 ZTF r 18.78 ± 0.02
SN 2018fsh 2458373.99 91.34 ZTF r 18.78 ± 0.02
SN 2018fsh 2458374.01 91.36 ZTF g 20.21 ± 0.11
SN 2018fsh 2458376.99 94.26 ZTF g 20.3 ± 0.05
SN 2018fsh 2458377.02 94.28 ZTF r 18.86 ± 0.02
SN 2020uik 2459109.11 23.41 ATLAS o 18.24 ± 0.07
SN 2020uik 2459111.1 25.34 ATLAS c 18.43 ± 0.04
SN 2020uik 2459113.12 27.3 ATLAS o 18.27 ± 0.03
SN 2020uik 2459115.09 29.21 ATLAS c 18.53 ± 0.07
SN 2020uik 2459115.1 29.22 ATLAS c 18.33 ± 0.12
SN 2020uik 2459126.12 39.92 ATLAS o 18.11 ± 0.02
SN 2020uik 2459127.12 40.89 ATLAS o 18.01 ± 0.1
SN 2020uik 2459130.97 44.63 ZTF r 18.23 ± 0.1
Note. All measurements are reported in the AB system and are corrected for Galactic line of sight reddening. The full table will be made available electronically on the
journal website and on WISeREP upon publication.
(This table is available in its entirety in machine-readable form.)
Figure 4. Light curves of SN 2018fsh (a) and SN 2020uik (b). Full symbols are
detections and empty triangles are 5σ upper limits. Vertical black dashed lines
mark the dates of spectroscopic observations.
Figure 5. Optical light curves of SN2019ape. Full symbols are detections and
empty triangles are P48 5σ upper limits. Vertical black dashed lines mark the
dates of spectroscopic observations.
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The Astrophysical Journal, 927:10 (22pp), 2022 March 1 Irani et al.
4.1. SN 2018fsh and SN 2020uik
4.1.1. Light-curve Properties
SN 2020uik is a SN IIP detected early in its plateau phase at
an absolute magnitude of Mr=−16.9 mag, which we adopt as
the peak luminosity. The plateau continues for 65 days until the
SN begins to fade. SN 2018fsh is a SN IIL—it was detected by
ATLAS near peak at a luminosity of c=−18.1 mag and was
observed again during its linear decline, 77 days after the
estimated time of maximum light. It continues to decline for an
additional 150 days until becoming undetectable.
4.1.2. Spectra
The spectral observations of SN 2018fsh and SN 2020uik
show that both appear to be spectroscopically normal SNe II.
SN 2018fsh was observed late in its evolution, and shows a
typical spectrum for a SN IIL at this phase. We show a
comparison with the closest Superfit match SN 2014G (de
Jaeger et al. 2019) in Figure 6. The spectrum shows strong Hα
and moderate Ca II emission. We interpret the absorption
feature at λ5900 as Na λ5890 and not He λ5876 in the absence
of additional features at λ6678 and λ7065 (Gal-Yam 2017).
Figure 9 shows a later nebular spectrum with Mg and Ca II
emission lines as well as a complex Hα emission profile. The
Hα feature has a broad and boxy profile, with velocities
ranging from −15,000 to 10,000 km s−1. Similar profiles have
been previously attributed to interaction of the fast outer ejecta
with CSM (Filippenko et al. 1994; Patat et al. 1995). This
interpretation is supported by the flattening of the light curve at
late times, e.g., as observed in all bands for SN 1993J
(Jerkstrand et al. 2015).
SN 2020uik has a more detailed spectroscopic sequence with
a typical Hα P-Cygni profile, Na I absorption at λ5890 as well
as Fe II absorption lines (λ4924, λ5018 and λ5169) and with
typical Ca II emission developing over time. Neither of the two
events shows significantly strong Ca emission compared to
other SNe II to be considered peculiar.
Figure 6. Comparison of the spectrum of SN 2018fsh to the spectrum of the
best matching Superfit result SN 2014G at a similar phase. The main
elements appearing in both spectra are marked with vertical lines. The dark line
is a binned version of the spectrum to guide the eye.
Figure 7. Spectral sequence of SN 2019ape. Phase is denoted in rest-frame
days. The main features appearing in the spectrum are marked with vertical
lines. Absorption features are blueshifted by 10,000 km s−1.
Figure 8. Spectral sequence of SN 2020uik. Phase is in rest-frame days.
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The Astrophysical Journal, 927:10 (22pp), 2022 March 1 Irani et al.
4.1.3. Limits on an Underlying Host Galaxy
We derive limits on the presence of a compact source at the
sites of SN 2018fsh and SN 2020uik using deep archival
imaging as described in Irani et al. (2019). For SN 2018fsh we
use Legacy Survey images (Dey et al. 2019) from the Beijing-
Arizona Sky Survey fields (Zou et al. 2017), and for
SN 2020uik we use deep PS1 imaging (Flewelling et al.
2020). Our 5σ limits are mg> 24.69 mag at the site of
SN 2018fsh and mg> 23.45 mag at the site of SN 2020uik
corresponding to luminosity limits of Mg=−10.73 mag and
Mg=− 11.91 mag respectively. In Figure 10 we show cutouts
of the explosion sites. In both cases, there are no sources within
a few kpc of the SN location.
4.2. SN 2019ape
4.2.1. Light-curve Properties
The light curves of SN 2019ape are shown in Figure 5.
SN 2019ape rose to an r-band peak luminosity of
Mpeak=−16.75± 0.05 mag, 17.1± 0.7 days after the explo-
sion in the SN rest frame. The time of peak is determined by
fitting a third-order polynomial to the r-band data around the
Table 3
Log of Spectroscopic Observations
SN Date Estimated Time Since Explosion (rest-frame days) Instrument Exposure Time (s) Airmass Grism
SN 2019ape 2019 Feb. 08 9.75 NTT/EFOSC2 900 1.49 13
SN 2019ape 2019 Feb. 10 12.56 LT/SPRAT 1200 1.02 red
SN 2019ape 2019 Feb. 12 14.33 P200/DBSP 900 1.05 600/4000
SN 2019ape 2019 Feb. 13 15.39 LT/SPRAT 1200 1.19 red
SN 2019ape 2019 Feb. 23 25.29 LT/SPRAT 1200 1.05 red
SN 2019ape 2019 Feb. 25 26.32 NTT/EFOSC2 2700 1.59 16
SN 2019ape 2019 Feb. 25 26.37 NTT/EFOSC2 2700 1.49 11
SN 2019ape 2019 Mar. 01 30.15 NOT/ALFOSC 2400 1.02 4
SN 2019ape 2019 Mar. 08 37.12 NTT/EFOSC2 2700 1.48 13
SN 2019ape 2019 Apr. 27 86 NTT/EFOSC2 2 × 2700 1.51 13
SN 2019ape 2019 Dec. 03 302.19 Keck/LRIS 1750 1.04 600/4000,400/8500
SN 2020uik 2020 Oct. 18 39.83 P60/SEDM 2250 1.52 IFU
SN 2020uik 2020 Oct. 25 46.44 NTT/EFOSC2 2700 1.13 13
SN 2020uik 2020 Nov. 17 68.69 NTT/EFOSC2 2700 1.35 13
SN 2020uik 2020 Dec. 08 89.03 NTT/EFOSC2 2700 1.35 13
SN 2020uik 2020 Dec. 08 89.06 NTT/EFOSC2 2700 1.19 16
SN 2020uik 2020 Dec. 22 102.6 NTT/EFOSC2 2700 1.27 13
SN 2018fsh 2018 Sep. 12 91.2 P200/DBSP 2 × 600 1.66 316/7500, 600/4000
SN 2018fsh 2019 Apr. 06 291.1 Keck/LRIS 1750 1.655 316/7500, 600/4000
Table 4
Photometry of SN Host Galaxies Analyzed in This Work
Instrument/Filter λeff (Å) SN 2003ky SN 2006ee SN 2006gy PTF10gqf PS1-12sk
GALEX/FUV 1542 18.92 ± 0.17 17.83 ± 0.03 20.25 ± 0.82 19.83 ± 0.05 19.27 ± 0.14
GALEX/NUV 2274 18.3 ± 0.08 17.85 ± 0.06 18.34 ± 0.24 19.87 ± 0.06 18.24 ± 0.06
SDSS/u 3595 16.89 ± 0.04 15.12 ± 0.05 15.14 ± 0.14 17.72 ± 0.09 16.54 ± 0.05
SDSS/g 4640 15.35 ± 0.01 13.43 ± 0.01 13.43 ± 0.08 16.16 ± 0.02 14.82 ± 0.04
SDSS/r 6122 14.62 ± 0.01 12.63 ± 0.01 12.63 ± 0.04 15.48 ± 0.01 13.99 ± 0.01
SDSS/i 7440 14.24 ± 0.01 12.19 ± 0.01 12.22 ± 0.04 15.08 ± 0.01 13.56 ± 0.01
SDSS/z 8897 13.95 ± 0.02 11.83 ± 0.03 11.92 ± 0.03 14.8 ± 0.04 13.27 ± 0.04
PS1/g 4776 15.38 ± 0.01 13.39 ± 0.03 13.4 ± 0.04 K 14.79 ± 0.06
PS1/r 6130 14.61 ± 0.01 12.68 ± 0.02 12.67 ± 0.09 15.5 ± 0.01 14.02 ± 0.06
PS1/i 7485 14.24 ± 0.01 12.28 ± 0.01 12.28 ± 0.04 15.12 ± 0.01 13.64 ± 0.04
PS1/z 8658 14.07 ± 0.01 12.04 ± 0.02 12.04 ± 0.05 14.95 ± 0.02 13.46 ± 0.04
PS1/y 9603 13.8 ± 0.03 11.8 ± 0.03 11.83 ± 0.04 14.67 ± 0.05 13.23 ± 0.04
2MASS/J 16620 13.69 ± 0.04 11.56 ± 0.03 11.57 ± 0.02 14.68 ± 0.05 12.87 ± 0.03
2MASS/H 12482 13.37 ± 0.03 11.36 ± 0.03 11.34 ± 0.02 14.43 ± 0.05 12.71 ± 0.04
2MASS/K 21590 13.55 ± 0.04 11.55 ± 0.03 11.51 ± 0.02 14.72 ± 0.05 12.83 ± 0.04
WISE/W1 33526 14.32 ± 0.01 12.34 ± 0.01 12.3 ± 0.01 15.25 ± 0.02 13.6 ± 0.02
WISE/W2 46028 14.96 ± 0.02 13.04 ± 0.01 12.94 ± 0.02 15.85 ± 0.02 14.29 ± 0.02
WISE/W3 120000 14.76 ± 0.06 13.56 ± 0.07 13.03 ± 0.03 15.53 ± 0.07 15.49 ± 0.16
WISE/W4 220000 16.19 ± 0.82 13.82 ± 0.23 12.39 ± 0.04 16.15 ± 0.56 >14.56
Note.
a All measurements are reported in the AB system and are corrected for Galactic line of sight reddening.
9
The Astrophysical Journal, 927:10 (22pp), 2022 March 1 Irani et al.
peak (10–30 days after texp), and the error is estimated by
varying the fit range and order. The decline of the light curve is
observed over the course of 100 days, with a re-brightening of
the g- and B-band light curves observed starting from t= 60
days and reaching an unusual secondary peak of g=
−14.6 mag at t∼ 80 days. The transient is then observed again
at t= 305 days at a luminosity of r=−13.0± 0.2 mag before
fading below the detection limit. The late-time decline of
2.5 mag over the course of 250 days is consistent with 56Co
decay (0.98 mag per 100 days; Woosley et al. 1989), but the
exact 56Ni mass cannot be measured directly due to the poor
light-curve sampling at late times.
4.2.2. Spectroscopic Comparison of SN 2019ape and Other SNe Ic
Qualitatively, the spectra of SN 2019ape are similar to those
of SNe Ic. In Figure 11 the spectra are compared with the well-
observed SNe Ic SN 1994I (Filippenko et al. 1995),
SN 2004aw, the best-fitting SN to SN 2019ape with Superfit
(Taubenberger et al. 2006), and SN 2007gr (Valenti et al. 2008;
Modjaz et al. 2014) around maximum light and at two weeks
past maximum. Around maximum light, the spectroscopic
features are similar in position and in strength among the
objects, in particular those associated with Fe II and Mg II in the
region bluewards of 5500Å. Of note is that the spectrum of
SN 2019ape at −7.5 days peaked at around 5500Å. This is
unlike the early spectra of SNe 2004aw and 2007gr which are
bluer despite being observed later in their evolution (e.g., the
spectrum of SN 2007gr at −4.6 days peaks at ∼4000Å). Over
the course of a week, the spectra of the comparison objects
gradually redden as they reach maximum light and the ejecta
cool. The SN 2019ape spectrum at −3.5 days is similar in this
respect to the comparison objects around peak or slightly after.
The spectrum is a very good match to the spectrum of
SN 2004aw at around +5 days. As time progresses the objects
gradually evolve to look similar, although SN 2019ape does not
display the narrow lines of SN 2007gr and retains the slight
blending of the Fe II lines in the blue part of the spectrum as
seen in SNe 1994I and 2004aw (for a discussion of this, see
Prentice & Mazzali 2017). It can be concluded that SN 2019ape
is a normal SN Ic supernova, albeit with some differences in its
pre-peak spectra, and the peculiar secondary peak in g-band.
4.2.3. Photospheric-phase Spectral Modelling
We model the spectra of SN 2019ape with a 1D radiative
transfer code which has been used extensively to model the
spectra of stripped-envelope SNe (SE-SNe) (e.g., Mazzali et al.
2000, 2002, 2006; Sauer et al. 2006; Prentice et al. 2018b;
Ashall et al. 2019; Teffs et al. 2021). The code is described in
detail by Mazzali & Lucy (1993), Lucy (1999), Mazzali (2000),
and is the source of a parameter study by Ashall & Mazzali
(2020). The model requires an input density profile, ejecta
composition, photospheric velocity, epoch, and luminosity
which it then uses to approximate the expanding SN ejecta,
Table 5
Photometry of SN Host Galaxies Analyzed in This Work (continued)
Instrument/Filter λeff (Å) PTF16pq SN 2016hil
b SN 2018fsh SN 2019ape SN 2020uik
GALEX/FUV 1542 19.04 ± 0.11 19.83 ± 0.08 19.47 ± 1.43 17.67 ± 0.05 19.77 ± 0.15
GALEX/NUV 2274 19.36 ± 0.07 20.42 ± 0.17 18.35 ± 0.47 16.57 ± 0.02 18.36 ± 0.06
SDSS/u 3595 16.25 ± 0.09 17.67 ± 0.08 16.67 ± 0.12 14.89 ± 0.03 K
SDSS/g 4640 14.49 ± 0.02 15.88 ± 0.03 15.13 ± 0.04 13.36 ± 0.01 K
SDSS/r 6122 13.66 ± 0.01 15.02 ± 0.02 14.34 ± 0.04 12.59 ± 0.01 K
SDSS/i 7440 13.22 ± 0.02 14.57 ± 0.02 13.93 ± 0.03 12.2 ± 0.01 K
SDSS/z 8897 13.0 ± 0.03 14.2 ± 0.04 13.62 ± 0.04 11.91 ± 0.02 K
PS1/g 4776 14.43 ± 0.02 15.84 ± 0.03 15.08 ± 0.02 13.47 ± 0.01 15.71 ± 0.03
PS1/r 6130 13.7 ± 0.01 15.09 ± 0.02 13.97 ± 0.02 12.74 ± 0.02 15.09 ± 0.03
PS1/i 7485 13.31 ± 0.01 14.64 ± 0.01 14.34 ± 0.02 12.46 ± 0.01 14.76 ± 0.03
PS1/z 8658 13.09 ± 0.01 14.47 ± 0.01 13.79 ± 0.04 12.13 ± 0.01 14.57 ± 0.07
PS1/y 9603 12.85 ± 0.02 14.16 ± 0.03 13.57 ± 0.07 11.86 ± 0.02 14.3 ± 0.08
2MASS/J 16620 12.59 ± 0.05 14.14 ± 0.05 13.32 ± 0.04 11.63 ± 0.02 14.07 ± 0.04
2MASS/H 12482 12.27 ± 0.05 13.85 ± 0.05 13.18 ± 0.04 11.49 ± 0.03 14.05 ± 0.05
2MASS/K 21590 12.56 ± 0.05 14.03 ± 0.05 13.37 ± 0.05 11.65 ± 0.02 14.28 ± 0.07
WISE/W1 33526 K 14.49 ± 0.01 14.08 ± 0.02 12.36 ± 0.01 15.0 ± 0.02
WISE/W2 46028 14.01 ± 0.02 15.13 ± 0.03 14.78 ± 0.02 13.0 ± 0.01 15.69 ± 0.02
WISE/W3 120000 14.54 ± 0.10 16.2 ± 0.12 16.12 ± 0.45 12.98 ± 0.06 17.16 ± 0.26
WISE/W4 220000 14.69 ± 0.57 14.9 ± 0.12 > 14.83 13.2 ± 0.19 16.35 ± 0.73
Notes.
a All measurements are reported in the AB system and are corrected for Galactic line of sight reddening.
b W3 photometry is estimated from the W2-W3 ALLWISE color of Irani et al. (2019) (see text).
Figure 9. The nebular spectrum of SN 2018fsh. Dashed colored lines denote
major features. Inset panel shows a zoom in of the Hα feature with wavelength
in units of velocity relative to the rest frame. The dark curve is a binned version
of the spectrum to guide the eye.
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The Astrophysical Journal, 927:10 (22pp), 2022 March 1 Irani et al.
which are assumed to be in homologous expansion. Radiation
is assumed to be emitted at a sharp inner boundary (the “the
inner photosphere”), following a blackbody distribution with
temperature Tbb, which is found through an iterative MC
process. The code follows the propagation of “photon packets”
through the SN atmosphere, as represented by the density and
abundance profiles. These packets can be subject to Thomson
scattering and line absorption in the model ejecta, both
fluorescence and reverse fluorescence are possible. The
interaction of photons and the gas redistributes the temperature
and determines the ionization and excitation states of the gas,
which are computed self-consistently using the nebular
approximation (Abbott & Lucy 1985; Pauldrach et al. 1996).
Finally, the emergent spectrum is found by calculating the
formal integral of the radiation field.
We modeled three spectra of SN 2019ape, one prior to r-
band maximum, one at maximum, and one a few weeks later.
As SN 2019ape shows spectral similarities to SN 2004aw, we
started with the density profile and abundance distribution from
the model found in Mazzali et al. (2017), which in turn is based
on the CO21 1D hydrodynamical model developed for
SN 1994I (Nomoto et al. 1994). This initial model was
modified using the scaling relations from Hachinger et al.
(2009) for the ejected mass Mej and the explosion kinetic
energy Ek until a model that reasonably reproduces the spectral
flux and line profiles is found, and then the abundances are
iteratively modified until the bulk of the features are well
reproduced. As we did not model the light curve in parallel
with the spectra, the values of Mej and Ek that we determined
are approximate. Additionally, the lack of early-time spectra
and photometry limit the accuracy of the determination of Ek
using this method (see Mazzali et al. 2017). Our modeling
suggests that a good fit is obtained using a density profile with
Mej= 2Me and Ek= 2× 10
51 erg, and a specific kinetic
energy that is similar to SN 2004aw (Ek,51/Mej≈ 1). As the
first modeled epoch is approximately 10 days after texp as
Figure 10. Deep archival images of the explosion sites of SN 2018fsh and SN 2020uik. PS1 g and r images were stacked to increase the signal at the site of
SN 2020uik. Concentric circles at 1, 2, 3 kpc are shown around the SN position.
Figure 11. Comparison of the (a) spectra and (b) r/R-band light curves of SN 2019ape to those of SN 2007gr (green), SN 2004aw (red), and SN 1994I (blue). The
spectra are corrected for both host and Milky Way extinction as described in the text.
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The Astrophysical Journal, 927:10 (22pp), 2022 March 1 Irani et al.
estimated in Section 2.4.2, we used two dummy shells to model
the high-velocity material properly. As we have no early
spectra, these two shells were primarily used to reduce high-
velocity line formation of certain elements. In addition, we use
an additional dummy shell between the second and third
modeled epochs (t∼ 14 days and t∼ 27 days respectively) as
this is an extensive gap in spectral evolution. The resulting
models are shown in Figure 12 with the abundances of each
shell given in Table 6.
The first modeled spectrum was obtained on 2019 February
8, ∼10 days from estimated explosion time and ∼7.6 days prior
to r-band peak. For this spectrum we find vph= 12,500 km s
−1
and L= 1.40× 1042 erg s−1. The model manages to capture
many of the spectral features well, with a few issues (see first
panel of Figure 12). The abundance at this phase is primarily
carbon (∼66%), with ∼30% neon and only 3% oxygen. A
larger oxygen abundance leads to an excessively strong O I
λ7774 feature in the synthetic spectrum. In the dummy shells
above this photosphere, the oxygen mass is reduced even
further, leaving a C and Ne rich outer shell. Comparatively, at
this epoch the models shown in Mazzali et al. (2017) had
approximately equal abundances of carbon and oxygen (35%).
The observed O I λ7774 line in this epoch is also noisy and
likely contaminated with a telluric line, which makes it difficult
to fit. As mentioned previously, a key difference between
SN 2004aw and SN 2019ape is that the spectrum of
SN 2019ape is redder and peaks at ∼5500Å rather than
∼4500Å. Two noticeable issues with the model are the
inability to replicate the peak near 5500Å and the weak NIR
Ca II line. The peak could be driven by re-emission from the
iron features near 5000Å or possibly other Fe-group elements,
however, the high abundances of Fe or Fe-group elements
needed to drive the flux upward in this region produce
absorption features that are far too strong as well as other lines
that are not observed. Increasing the total luminosity can also
reproduce the peak at 5500Å but produces far too high a flux
level at wavelengths redder than 6000Å. The second issue is
that the Ca II NIR feature is too weak, which is likely due to the
model having too high a temperature at this phase, leading to
the over-ionization of Ca. Lowering the temperature produces a
Figure 12. Best-fit model spectra for the selected spectra of SN 2019ape.
Table 6
Parameters and Selected Abundance Fractions for the Model Shells
t (days) vph (km s
−1) Tbb (K) C O Ne Na Mg Si S Ca
56Fe 56Ni
Dummy shell 23000 K 0.7 0.004 0.29 0.0 0.005 0.0005 0.00025 0.0 0.0001 0.0001
Dummy shell 17000 K 0.7 0.0065 0.29 0.0 0.0025 0.0005 0.00025 3 × 10−6 0.0001 0.0001
10 12500 7249.6 0.66 0.035 0.3 0.0005 0.0025 0.0015 0.0006 7 × 10−6 0.0001 0.0005
14 10500 7028.2 0.5 0.2 0.3 0.00055 0.001 0.0022 0.002 0.0 0.0005 0.002
Dummy shell 8500 K 0.5 0.3 0.15 0.001 0.001 0.015 0.035 2 × 10−6 0.0025 0.0025
27 6500 6327 0.5 0.3 0.02 0.002 0.001 0.015 0.05 1 × 10−6 0.0025 0.05
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The Astrophysical Journal, 927:10 (22pp), 2022 March 1 Irani et al.
worse fit to other parts of the spectrum, and increasing the Ca
abundance is inconsistent with the later spectra.
We next model a spectrum that was obtained four days later,
on 2019 Feb. 12 (∼14 days after the explosion and 2.8 days
before the peak). The input parameters were vph= 11000 km
s−1 and L= 1.64× 1042 erg s−1. This spectrum is quite similar
to the one at - ~t t 10exp d but is marginally redder,
suggesting a lower temperature. The abundances are similar
to those of the previous spectrum, as the velocities only differ
by 1500 km s−1 and therefore represent shells located close
within the ejecta profile. Although the main features of the
spectrum are replicated, owing to the lower temperature the
Ca II NIR and H&K features are stronger in this model than in
the previous one.
The final spectrum modeled was obtained on 2019 Feb. 25,
∼27 days after the explosion and 9.4 days after the peak. Here,
we used vph= 6500 km s
−1 and L= 1.23× 1042 erg s−1. As
before, many of the features in the spectrum are replicated by
the model, apart from the peak at 5500Å, which shows an Fe II
line with a rest wavelength of 5534Å that is clearly not visible
in the observed spectrum. Comparing to the other SNe of
similar epochs in Figure 11, the line is seen in SN 2004aw,
SN 2007gr, and possibly in SN 1994I. However, the Fe
abundance is required to reproduce other features, suggesting
that the Fe abundance at higher velocities may be too low. But,
as discussed previously, increasing the Fe abundance in the
outermost regions produces unwanted lines in those epochs.
Several lines are observed in the spectrum in the region
between 6600 and 7100Å that are not reproduced by the
model. These are often blends of C I and Fe-group elements.
Carbon is still mostly singly ionized, and the issues with the Fe
distribution still holds. The O I abundance is still low during
this phase, but the O I 7774Å line is saturated, and is less
responsive to abundances changes at this epoch. The absorption
near 9300Å is possibly due to strong C I features that are only
partially replicated.
4.2.4. Star Formation of the Host Galaxy
Massive stars are associated with regions of elevated star
formation which can be traced by UV continuum and Hα
emission (Kennicutt 1998). Here we consider both star
formation in the local environment of SN 2019ape and the
total star formation rate of its host galaxy. De et al. (2020)
acquired a deep nebular spectrum of SN 2019ape ∼ 300 days
after the explosion. The 2D spectrum reveals a compact Hα-
emitting region in close proximity to the SN site on top of the
narrow absorption feature observed throughout the slit. In
Figure 13, we show a cutout of the 2D image with the trace of
SN 2019ape and the Hα emitting region highlighted. Using
SAOImageDS9 (Joye & Mandel 2003) we measured the
strength of the Hα emission relative to the local absorption
background. After correcting for MW extinction we find a flux
of fHα= 1.4± 0.5× 10
−16 erg s−1 cm−2 and an integrated Hα
luminosity of 3.1± 1× 1038 erg s−1 - a typical value for an H II
region (Kennicutt & Edgar 1989). We convert this to a star
formation rate (SFR) using the calibration by Kennicutt (1998)
and find that this regions forms 2.4× 10−3Me yr
−1. Globally
the host galaxy is relatively UV bright, with a color of
NUV− rPS1= 4.03± 0.03 mag indicating it has undergone an
episode of recent (<100 Myr) star formation. (Suh et al. 2011;
Yi et al. 2005).
4.3. Host-galaxy Sample Properties
We use the host photometry of the objects in our sample and
the archival photometry for the BTS SN hosts to derive their
SFR and stellar masses. Traditionally, SFR can be derived
using UV luminosities that are dominated by massive stars
(e.g., Kennicutt 1998; Salim et al. 2007). However, this tracer
is sensitive to dust attenuation (e.g., see Calzetti et al. 1995;
Buat et al. 1999). To compensate for the effects of dust
attenuation, we use the UV SFR indicator calibrated by Salim
et al. (2007). Stellar mass values are estimated from the W2
brightness using the calibration of Wen et al. (2013). We report
the derived SFR and stellar mass estimates in Table 7, along
with the mean SFR and stellar mass estimates for Galaxy Zoo
spirals and ellipticals. In Figure 14 we plot the SFR of BTS
CCSNe hosts, our sample of CCSNe in elliptical galaxies and
BTS SNe Ia in elliptical galaxies. The elliptical host galaxies of
CCSNe show more star formation on average compared to
the general elliptical galaxy population - -+ -M0.41 yr0.230.53 1
compared to -+ -M0.09 yr0.050.09 1 for Galaxy Zoo ellipticals and
-+ -M0.76 yr0.721.47 1 for the general CCSN host-galaxy popula-
tion. CCSNe in elliptical galaxies are also more massive than
most elliptical galaxies, with ´-+ M2.76 101.493.24 10 compared
to an average of ´-+ M0.83 100.581.95 10 for the Galaxy Zoo
Figure 13. 2D cutout of the nebular spectrum of SN 2019ape. The trace of the SN is faint and becomes significant relative to the galaxy background only at the [O I]
nebular feature. Both the Hα and weaker [N II] narrow lines extend to the SN site, indicating an underlying star-forming region. The 2D frames are sky subtracted
using the sky-subtraction routine of LPipe, which removes some of the host-galaxy emission lines for larger galaxies.
13
The Astrophysical Journal, 927:10 (22pp), 2022 March 1 Irani et al.
ellipticals. The high SFR of CCSNe elliptical hosts can be
explained by their higher mass. The specific SFR (sSFR; i.e.,
the SFR per unit mass) of CCSNe ellitpicals hosts is
´-+ - -1.49 10 yr0.872.08 11 1 compared to ´-+ - -1.06 10 yr0.521.03 11 1 for
galaxy zoo ellitpicals, and ´-+ - -2.60 10 yr2.544.99 10 1 for the hosts
of BTS CCSNe.
5. Discussion
In this paper, we have presented and analyzed three CCSNe
occurring in elliptical galaxies from the ZTF BTS experiment
and their hosts. In this section we will discuss the implications
of our results regarding star formations in ellipticals, as inferred
from the population of CCSNe which they host.
5.1. CCSNe as Representative Members of Their Spectroscopic
Classes
Finding a CCSN in an elliptical galaxy can be either a sign of
residual star formation, or that the progenitor of the event in
question was not a massive star. The most recent example of
the later are the class of Ca-rich Type Ib supernovae(Perets
et al. 2010). While these transients have spectra consistent with
SNe Ib near maximum light, they occur predominantly in
passive environments and galaxy outskirts, which argues
against a massive star origin (e.g., Perets et al. 2010; Kasliwal
et al. 2012; Lunnan et al. 2017, and most recently De et al.
2020). In addition to their remarkable locations, Ca-rich SNe
display peculiar features—strong Ca emission lines in their
nebular phase, and a lower luminosity compared to typical
SNe Ib.
A non-massive-star origin has been suggested for individual
CCSNe offset from elliptical galaxies, such as (1) for PS1-12sk
(Sanders et al. 2013; Hosseinzadeh et al. 2019), where deep
HST UV imaging excludes local star formation, and (2) for
SN 2016hil (Irani et al. 2019), where a double peaked light
curve and a low metallicity spectrum were observed. However,
conclusions regarding the (potentially) peculiar properties of
CCSNe in elliptical host galaxies were difficult to reach based
on isolated events, and due to noisy and sparsely sampled
photometry and spectroscopy in the case of SN 2016hil.
Here, we consider the combined properties of SNe II in
ellipticals, which we can now study as a population. Figure 15
shows the peak luminosities of Type II SNe analyzed in this
work, compared to the peak-luminosity distribution of BTS
SNe II in our comparison sample. With only 7 SNe II, our
sample is too small for a meaningful two-sample Kolmogorov–
Smirnov (KS) test of the two peak luminosity distributions. We
compare the mean and the standard deviations of the two
distributions instead. Our sample of SNe II in ellitpicals has a
mean peak absolute magnitude of −17.3± 1.0 mag, consistent
with −17.8± 0.8 mag for all spectroscopically regular SNe II
in the BTS sample.
Unfortunately, we do not have enough data to compare the
spectral properties of SNe II in ellipticals to the general SN II
population. However, we point out that absence of strong Ca
emission in the nebular spectrum of SN 2018fsh and
SN 2019ape, (compared to Ca-rich SNe Ib/c or Ia; De et al.
2020), and the typical spectral evolution of SN 2020uik,
suggest these two SNe are typical SNe II. The complex Hα
profile seen in the nebular spectrum of SN 2018fsh has a broad
and boxy profile, extending to high-velocities. These were
previously seen for the well observed SN 1993J and SN 1998S
and interpreted as signatures of late-time interaction with
circumstellar material (Filippenko et al. 1994; Patat et al. 1995;
Pozzo et al. 2004). Sollerman et al. (2021) discuss SNe with
similar nebular Hα extensively. The presence of extended
circumstellar material (CSM) around the progenitor of
SN 2018fsh could indicate some SNe II form through exotic
formation channels, such as mergers of intermediate-mass stars
as outlined in Zapartas et al. (2017), or a common-envelope
phase as suggested by Soker (2019). Zapartas et al. (2017)
estimates that such binary interaction could account for up to
15% of SNe II. It remains to be seen if such signatures are
common for SNe II with elliptical host galaxies.
Figure 14. SFR and stellar masses for (1) BTS SNe Ia in elliptical galaxies
(black crosses), (2) BTS CCSNe (green circles), (3) our sample of CCSNe in
ellipticals (magenta stars). Diagonal gray dashed lines are lines of equal sSFR,
and red and blue contours correspond to Galaxy Zoo ellipticals (which satisfy
the color criteria described in Section 2) and Galaxy Zoo spirals. The top and
right panels show the corresponding 1D kernel density estimates using the
same color scheme as the 2D plot.
Table 7
SN Host-galaxy Properties Derived in This Work
SN Host SFR (Me yr
−1)
Mass
(109 Me)
SN2003ky NGC 4001 1.18 ± 0.09 37.5 ± 1.0
SN2006ee NGC 774 0.17 ± 0.01 19.6 ± 0.5
SN2006gy NGC 1260 0.18 ± 0.04 36.4 ± 1.0
PTF10gqf WISEA J150350.31
+553738.
0.26 ± 0.01 13.9 ± 0.4
PS1-12sk RXC J0844.9+4258 1.62 ± 0.09 98.7 ± 3.0
SN2016hil WISEA J011024.51
+141238.
0.26 ± 0.05 50.9 ± 1.9
PTF16pq CGCG 091-056 0.16 ± 0.01 32.7 ± 0.9
SN2018fsh MCG +07-18-013 0.43 ± 0.19 15.2 ± 0.4
SN2019ape NGC 3426 1.22 ± 0.02 49.0 ± 1.3
SN2020uik WISEA J080154.84-
064527.
0.4 ± 0.02 5.6 ± 0.2
K Galaxy Zoo ellipticalsa -+0.09 0.050.09 -+8.27 5.7919.33
K Galaxy Zoo spiralsa -+0.43 0.280.78 -+2.43 1.715.69
Note.
a Values quoted here represent the sample mean and standard deviation.
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The Astrophysical Journal, 927:10 (22pp), 2022 March 1 Irani et al.
While our sample only contains a single SN Ic, we
demonstrated in Section 4.2.2 that SN 2019ape is not a unique
event in most respects—both by comparison to other events
and by our modeling of SN 2019ape in 4.2.3. The later
indicates that the abundances, ejected mass and kinetic energy
are typical of a normal SN Ic when compared to a sample of
events (Prentice et al. 2016, 2018a). Its peak luminosity of
Mr=−16.75 mag is close to the mean peak luminosity in the
BTS sample (−17.3± 0.5 mag) and the light-curve evolution is
typical (Prentice et al. 2018a). The only unusual aspect is the
secondary g-band peak. It might indicate interaction with
extended CSM at later times, as for example observed by Ben-
Ami et al. (2014) or Gutiérrez et al. (2021). Similarly to
SN 2018fsh, the presence of extended CSM might indicate
binary evolution is responsible for the formation of the
progenitor star of SN 2019ape. However, given the rest of its
properties and the location of the event, we consider it unlikely
that SN 2019ape emerged from an unusual SN Ic progenitor. In
particular, the estimated ejected mass, chemical abundance
(dominated by unburned carbon) and energy point toward a
massive progenitor. We conclude that our sample of events in
elliptical galaxies is overall consistent with having properties
similar to the general population of CCSNe.
5.2. Localized Star Formation in Elliptical Galaxies
Based on our observations of the SN sites, we can separate
the sample of CCSNe in ellipticals into two groups—the SNe
which are located close to compact star-forming knots, and
those that are not. A good example of the former is SN 2006gy,
which exploded near the center of an early-type galaxy (Ofek
et al. 2007; Smith et al. 2007). SN 2006gy exploded near a
region showing signs of localized star formation. This is
indicated by a nearby dust lane and compact Hα emission
interpreted as an H II region (Ofek et al. 2007; Smith et al.
2007). However Jerkstrand et al. (2020) identify neutral iron
lines in one of the spectra of SN 2006gy, and argue it is
consistent with a SN Ia embedded in a shell of circumstellar
material, possibly contradicting a massive star origin. Similarly
to the site of SN 2006gy, the localized Hα emission extending
to the site of SN 2019ape is most likely an indication of a
nearby H II region where the progenitor star could have been
formed. SNe Ic are often associated with Hα emission in their
host galaxies, supporting a young progenitor population even
when compared to other CCSNe types (Anderson et al. 2015).
The same might be true for SNe Ic observed in elliptical
galaxies. This would imply that the initial mass function of
stars formed in H II regions in elliptical galaxies extends to
massive (…8Me) stars.
5.3. Extended Star Formation or Faint and Diffuse Satellites?
In addition to SNe occurring near sites of active formation,
we identify a second group of SNe that occurs in the outskirts
of their elliptical hosts, with no signs of localized star
formation. In all cases in which the background from the
apparent host galaxy was faint enough, we obtain strong limits
on the presence of an underlying host galaxy. Limits on the
luminosity of hypothetical faint hosts range from −10 mag to
−12 mag, putting all these hosts at the low end of the CCSN
host-galaxy luminosity distribution as presented in Schulze
et al. (2021).
Next, we consider whether CCSNe are typically located at
larger offsets from their elliptical host galaxies compared to the
host-offset distribution of the general CCSN population, and
compared to offsets of SNe Ia in elliptical galaxies. We begin
by inspecting the comparison between the offset distributions
of SNe Ia in ellipticals and our sample of CCSNe in ellipticals.
The right panel of Figure 16 shows the offset distribution of the
BTS SNe Ia in ellipticals, CCSNe, and the combined sample of
CCSNe in ellipticals. We show only SNe that are offset by less
than 30 kpc (projected) or 90″, the limits of the automatic cross
checks presented by Perley et al. (2020). We expect this to
cover the vast majority of CCSNe, as the largest offsets in the
(i)PTF sample were 37 kpc (Schulze et al. 2021). On the left
panel of the same figure we show the physical offsets and the
corresponding host-galaxy mass, along with the average 80%
light radius, r80[M*], derived using the low-redshift mass-size
relation of Mowla et al. (2019). Schulze et al. (2021)
demonstrated (their Figure 11) that the majority (>85%) of
CCSNe occur at distances smaller than r80.
The number of SNe in our sample is too low for significant
results from a two-sample KS test, but we can formulate an
alternative statistical test. We observe that 5% of SNe Ia with
elliptical host galaxies are detected at projected offsets larger
than 22.5 kpc. We define the null hypothesis as the case in
which CCSNe in ellipticals come from the same offset
distribution as SNe Ia: For a total of 9 SNe, we expect on
average ∼0.5 SNe at offsets larger than 22.5 kpc (upper 5% of
the Ia sample distribution). Assuming a Poisson distribution,
the probability of finding three or more SNe in this range is
then 1%, so that the null hypothesis is rejected with a
confidence of 99%. We note that this test is sensitive to the
position of the threshold. For example, repeating this test for all
SNe at distances larger than 17 kpc (upper 10% of the Ia
sample distribution) will result in less significant results (95%
rejection). Repeating this analysis with r/r80[M*] gives similar
results—the probability that 3 of 9 SNe have offsets larger
than>2 r80 is less than 3%, assuming the offset distribution of
SNe Ia with elliptical hosts. To conclude, we find tentative
evidence that CCSNe are typically located at larger offsets from
their host galaxies compared to SNe Ia in the same host-galaxy
population. However, a larger sample is needed in order to
reach a high statistical significance.
Figure 15. The peak r-band absolute magnitude cumulative distributions for
SNe II in elliptical galaxies (blue curve) compared to SNe II from the BTS
survey (green curve).
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The Astrophysical Journal, 927:10 (22pp), 2022 March 1 Irani et al.
A possible explanation for the high offset of CCSNe in
elliptical galaxies is a reduced detection efficiency at low
offsets on top of the high surface brightness center of their
elliptical hosts. Foley (2015) suggested this option to explain
the lack of Ca-rich SNe Ib at low offsets from their host
galaxies. Frohmaier et al. (2017) calculated the recovery
efficiency of the PTF pipeline and found it was lower in regions
of high surface brightness, but Frohmaier et al. (2017) later
found that this is not enough to explain the large offsets
observed for Ca-rich transients (Kasliwal et al. 2012). ZTF data
should be less susceptible to this bias than PTF was, since the
new ZTF camera provides substantially higher image quality,
and the optimal image subtraction of Zackay et al. (2016)
provides much cleaner subtraction; we thus estimate this effect
should be even weaker in our BTS sample. Still, a larger
homogeneous sample is needed to quantify this effect for
CCSNe in elliptical host galaxies.
An extended offset distribution for CCSNe in elliptical host
galaxies compared to the progenitors of SNe Ia has significant
implications for the formation of their progenitor stars.
An offset between the locations of SNe Ia and CCSNe in
ellitpicals could reflect an inside-out growth (Sánchez-Bláz-
quez et al. 2007; Pérez et al. 2013) in some massive ellipticals.
While the SNe Ia originate from an older stellar population
closer to the center of the massive hosts, CCSNe could explode
in regions where the host galaxy is accreting gas from the IGM.
This would be in agreement with the findings of Salim et al.
(2012), who found galaxy-scale star formation in UV-excess
early-type galaxies can extend to large offsets. Gomes et al.
(2016) found the extended star formation in the periphery
of early-type galaxies can take the form of faint (24
μr(mag/,″) 26) spiral features which possibly indicate
inside-out growth. However, such low-surface-brightness
features are excluded for both SN 2016hil and PS1-12sk, but
are still an option for SN 2018fsh SN 2020uik and PTF10gqf.
It is possible that the SNe we observe do not originate from
the ellipticals themselves, but from a different stellar population
nearby. This option is supported by some evidence that the
space between elliptical galaxies might not be completely
empty. in addition to having a large offset distribution
extending to regions with apparently no stellar populations
(Kasliwal et al. 2012), Ca-rich SNe prefer group and cluster
environments (Lunnan et al. 2017). Interestingly enough, PS1-
12sk exploded in a bright cluster environment as noted by
Sanders et al. (2013), who raised the possibility this might be
evidence for star formation in galaxy cluster cooling flow
filaments. Similarly, SN 2018fsh occurred in the compact
group V1CG 538 (Lee et al. 2017).
However, out of five objects that do not coincide with their
elliptical host galaxy, only two are possibly associated with a
group or cluster environment. We consider this preliminary
evidence that star-forming cooling flows are not the main
channel of star formation near elliptical galaxies. Gal-Yam
et al. (2003) measured the fraction of cluster SNe Ia originating
from an intergalactic stellar population (i.e., those which
originate outside of galaxies) to be 20%. In our sample, all SNe
detected in group or cluster environment were offset from their
putative host, indicating that this fraction is significantly
different in CCSNe near ellipticals. However, a larger sample is
needed to measure this fraction with high significance. While
not part of our sample, we also note that the SN II A399 11 19
0 (Graham et al. 2012) occurred in a nearby galaxy cluster, and
is not offset from its host galaxy. Ruiz et al. (2014) explore a
sample of 1000 ellipticals and find that the majority have small
satellites (down to a mass ratio of 1:400) with an average
projected distance of ∼59 kpc from their parent galaxy, that
contain 8% of their stellar mass. However, such galaxies are
excluded by our deep limits at the SN sites. Another possibility
for the origins of offset CCSNe can be found in the work of
Sedgwick et al. (2019), who recently demonstrated that a
population of star-forming low-surface-brightness galaxies
(LSBGs) host many of the seemingly hostless SNe. These
LSBGs can have significant star formation activity, like the
nearby UGC 2162. This ultra-diffuse galaxy has a low (but not
negligible) SFR of 0.01 Me yr
−1, but with a very low surface
brightness of 24.4 mag/,″ (Trujillo et al. 2017). This would
translate to an integrated absolute magnitude of −7 mag in the
optical. Such a faint and extended object would be difficult to
detect when located on top of the diffuse emission at the
outskirts of a massive elliptical at a redshift of 0.02. While such
Figure 16. Panel (a) shows the projected physical offsets of CCSNe in ellipticals (blue stars) and stellar mass of their host galaxies. BTS Ia in ellipticals (red circles),
and BTS CCSNe (green circles) are shown for comparison. The black dashed line represents the average 80% light radius corresponding to the host-galaxy stellar
mass. Panel (b) shows the cumulative distribution of the physical offsets for all three SN populations using the same color scheme.
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The Astrophysical Journal, 927:10 (22pp), 2022 March 1 Irani et al.
an ultra-diffuse host is ruled out in the case of PS1-12sk
(Hosseinzadeh et al. 2019), it has not been excluded for SNe II
in the outskirts of elliptical galaxies.
If the host galaxies of offset CCSNe are satellites of massive
galaxies, they would constitute a small fraction of CCSNe in
their typical host galaxies, and could erroneously be associated
with nearby more luminous hosts. However, in elliptical
galaxies which host much fewer CCSNe, such satellite
galaxies could host a larger fraction of the observed SNe. To
test this hypothesis, we select CCSNe from the BTS and PTF
samples that occur at offset of…15 kpc from massive
( ( [ ]) >M Mlog 10odot ) galaxies. We manually examine the
deepest publicly available survey data (if possible using the
Legacy Survey or otherwise PS1 images) and exclude all cases
where the SN occurred on or very close to pronounced
structures that are part of the host galaxy, such as spiral arms
extending to the SN location, or elevated (>3σ) emission
compared to the local background. We find the fraction of
highly offset CCSNe occurring in elliptical compared to
nonelliptical hosts is 0.33 (0.17–1.57; 95% confidence
interval). This value is consistent with the fraction of massive
ellipticals of all massive ( ( [ ]) >M Mlog 10) galaxies in the
Galaxy Zoo sample—0.33 (0.30–0.40; 95% confidence inter-
val). To reduce the selection bias, we selected a low-z
(0.025< z< 0.032) sample such that the redshift distributions
of elliptical galaxies, spiral galaxies, and all galaxies (including
those with irregular or uncertain morphological classifications)
match.
We conclude that the most likely explanation for the highly
offset distribution of CCSNe near ellipticals is one of the
following
1. a population of ultra-diffuse satellite star-forming
galaxies near massive elliptical galaxies. The rate of
highly offset CCSNe around massive ellipticals is hence
similar to their rate around all massive galaxies. Due to
the large number of CCSNe occurring in massive star-
forming galaxies, the few offset events are unremarkable,
but with very few events occurring in massive ellipticals,
the offset population, perhaps arising from very faint
satellites, stands out. Deeper observations of the location
of our sample events are needed to establish this.
2. Some cases can be explained by extended and faint spiral
features, or extended galaxy-scale star formation due to
accretion of gas from the IGM. The latter would indicate
inside-out growth of their elliptical host galaxies. Future
studies of the host galaxies of the CCSNe in our sample
can also confirm or exclude this possibility.
5.4. The Star Formation Fraction in Elliptical Galaxies
We attempt to measure the formation rate of massive stars in
elliptical galaxies through the fraction of CCSNe occurring in
such environments in a fixed volume. The connection between
the SFR and the CCSN rate has been previously established.
Kennicutt (1984) found a linear correlation between the SFR
and the CCSN rate, and used it to estimate a lower mass limit
for the progenitor mass of CCSNe. Botticella et al. (2012)
assume a lower mass limit of 8 Me and derive a SFR for a
complete sample of galaxies in the local universe. Their
estimate agrees with the SFR implied from their FUV
luminosities. Maoz et al. (2011) used a sample of 119 CCSNe
from the Lick Observatory SN search (LOSS; Leaman et al.
2011; Li et al. 2011) and estimated a rate of 0.01± 0.002 SNe
per Me. If the CCSN rate per Me is fixed across galaxy type,
the fraction of CCSNe occurring in elliptical galaxies should
reflect the fraction of the total star formation in their host
galaxy population. Recently, Schulze et al. (2021) provided
additional support for this claim by showing that the SN host-
galaxy mass distributions are consistent with those of star-
forming galaxies weighted by their star formation activity.
When measuring the fraction of CCSNe in elliptical galaxies,
the different colors of elliptical and spiral galaxies could create
a selection effect especially when considering galaxies with
both UV–optical and MIR color information. Most notably, the
redder UV–optical color of elliptical galaxies makes them less
likely to have archival GALEX photometry compared to spirals
at a similar optical brightness. However, our MIR photometry
is not biased against ellipticals in the same way due to the
brighter W2 magnitudes of massive ellipticals. W3 magnitudes
distribute similarly for spirals and ellipticals. Figure 17 shows
the magnitude distribution for the WISE/W2 band and
GALEX/NUV band for all galaxies in the BTS Ia sample for
elliptical and nonelliptical hosts. We illustrate that while
ellipticals are less likely to be detected by GALEX at larger
distances due to their faint NUV brightness, they are more
likely to be detected by WISE. Thus, we derive estimates based
on hosts with both UV–optical and MIR colors and based on
hosts with MIR colors alone (using both definitions discussed
in Section 2.1). A consistent result between both calculations
will ensure that the selection effects in our samples are not
strong. We also include a third estimate of the rate compared to
Figure 17. W2 (left) and NUV (right panel) magnitude distribution for all BTS SNe Ia, BTS SNe Ia in elliptical galaxies and BTS SNe Ia in nonelliptical galaxies.
17
The Astrophysical Journal, 927:10 (22pp), 2022 March 1 Irani et al.
all CCSNe, regardless of their host-galaxy association. The
resulting fractions are:
1. = = -+R 0.4 %CC 2478 0.30.5 using both W2−W3 and NUV-r
color
2. = = -+R 0.3 %CC 3888 0.10.4 based on our definition for
ellipticals using only the W2−W3 color and compared
to all CCSNe associated with host galaxies.
3. = = -+R 0.3 %CC 3959 0.10.3 based on our definition for
ellipticals using only the W2−W3 color, and compared
to all CCSNe regardless of their host-galaxy association.
Statistical errors reflect the exact binomial 68% confidence
interval on the reported values. We now compare the measured
fraction of CCSNe in ellipticals (∼0.4%) with the fraction of
star formation ellipticals accounted for out of the total star
formation produced by all galaxy types, calculated using the
method of Cortese (2012) applied to UV and MIR
observations.
We sum the total SFR of all Galaxy Zoo ellipticals which
satisfy the color criteria in Section 2.1, and are within the range
0.025< z< 0.032, and compare it to the fraction of the total
SFR in this redshift range in all galaxy types. We find that in
this sample, the fraction of the total SFR produced by ellipticals
is 1± 0.01%, slightly higher (∼2σ) than the star formation
inferred from the fraction of CCSNe in elliptical galaxies
compared to all CCSNe. This could be explained due to
additional UV emission by Active Galactic Nuclei (AGN) and
old stellar populations (Jura 1982; Crocker et al. 2011), or due
to an incomplete sample in the low-mass range of spiral
galaxies (which host a significant fraction of CCSNe; Taggart
& Perley 2021). Alternatively, this difference could reflect an
underestimate of the SFR in spiral compared to elliptical
galaxies due to the different total extinction of the host galaxies
populations, or due to a different rate of failed SNe in both
environments.
Our results are in significant tension with those of Kaviraj
(2014), who claim that early-type galaxies (elliptical and
lenticular) account for 14% of the star formation budget at
z< 0.07. The sample in the study by Kaviraj (2014) is limited
to bright <16.8 mag galaxies, which account for 52% of the
total star formation in our general Galaxy Zoo sample, but only
for 5% of star formation in ellitpicals. Thus ellipticals are over-
represented in their sample.
Our findings highlight the importance of CCSN rates as
independent tracers of SFR across a large range of sSFR and
galaxy brightness, while preventing the severe selection effects
associated with the low end of the galaxy brightness
distribution. The planned Rubin Observatory Legacy Survey
of Space and Time (LSST; Ivezić et al. 2019) is expected to
increase the rate of CCSN detections by an order of magnitude
in upcoming years. This will increase the number of CCSNe
detected in elliptical hosts by an order-of-magnitude, allowing
an in-depth study of the nature of star formation in and around
elliptical hosts. However, we caution against using CCSNe as
estimators of star formation without taking proper care to
remove the significant contamination due to misclassified
galaxies or SNe, or due to a false association of the SN with the
host galaxy.
Della Valle et al. (2005) previously estimated elliptical
galaxies might host up to 3% of CCSNe, based on a sample of
SNe Ia in ellitpicals from the Asiago SN survey (Cappellaro
et al. 1999). Our findings place more stringent constraints on
the rate of CCSNe in ellipticals compared to those obtained in
previous studies by an order of magnitude. Recently, Sedgwick
et al. (2021) published a study of 36 CCSNe occurring in
elliptical galaxies out of red photometrically classified CCSNe
isolated from the SDSS-II survey at z< 0.2, suggesting that the
fraction of CCSNe occurring in elliptical galaxies is signifi-
cantly higher than the fraction we measure in this study (∼8%
compared to our ∼0.4%). We point out that a population
comprising of 8% of CCSNe would stand out in the
spectroscopically complete BTS. Applying this rate to the
478 CCSN hosts with UV and MIR color information, we
would expect to find 38± 6 CCSNe in elliptical galaxies,
compared to the 2 found in our sample—a>5σ difference. We
conclude that the fraction of CCSNe in ellipticals given by
Sedgwick et al. (2021) is over estimated. This could be due to a
contamination of their sample by misclassified SNe Ia.
Sedgwick et al. (2021) define a confidently classified CCSN
as having probability of PIa< 0.05 for being a SN Ia, based on
their light curves alone. Since SNe Ia vastly outnumber CCSNe
in elliptical hosts (in our sample, 240:2) the contamination of
the CCSN sample due to falsely classified SNe Ia is likely
significant, and could dominates their sample.
6. Summary and Conclusions
In this study, we conducted a systematic search for elliptical
host galaxies of CCSNe in the ZTF BTS—a spectroscopically
complete survey. In Section 2, we outlined the selection
process for the candidates. We identified elliptical galaxies
based on their UV–optical and MIR colors, or based on the
MIR color alone. A control sample of morphologically
classified galaxies confirms that we achieve a good separation
between elliptical and spiral galaxies. We further visually
verified that the morphology of the host galaxies is elliptical,
with no disk or bar structures.
We identified three CCSNe that seem to be associated with
elliptical galaxies. We presented their light curves, spectra, and
host-galaxy photometry in Section 3, and analyzed our
observations in Section 4. SN 2018fsh and SN 2020uik are
spectroscopically regular SNe II which exploded in the
outskirts of massive ellipticals with no signs of an alternative
underlying host. SN 2020uik shows typical spectra for SNe II
during its photospheric phase, while SN 2018fsh shows an
extended and boxy Hα profile in its nebular spectrum, a
signature of CSM interaction. SN 2019ape is a SN Ic located in
a massive elliptical near a compact star-forming region. Its g-
band light curve shows a late-time second peak—a possible
signature of extended CSM interaction, previously observed in
other SNe Ic. Aside from this feature, a comparison to other
SNe Ic shows it is a regular SN Ic and modeling a series of
photospheric spectra reveals it had typical explosion properties.
These, along with its location near a star formation site, point to
a massive star origin.
We combine these objects with 7 literature CCSNe satisfying
our criteria, and analyzed the properties of the combined
sample of SNe and their host galaxies. We derived stellar
masses and SFRs for the hosts and compared these to a control
sample of SNe Ia in elliptical galaxies and BTS CCSNe. Our
analysis concludes that elliptical galaxies hosting CCSNe are
broadly consistent with the general population of ellipticals.
We discussed the implications of our results in Section 5. We
demonstrated that the peak r-band absolute magnitudes of SNe
II in ellipticals are consistent with those of a sample of SNe II
18
The Astrophysical Journal, 927:10 (22pp), 2022 March 1 Irani et al.
from the BTS. We presented preliminary evidence that the
offset distribution of CCSNe from their putative hosts extends
to large offsets compared to both the BTS CCSN sample and a
sample of SNe Ia in elliptical galaxies. However, this is not
determined with high statistical significance, and verifying this
requires a larger sample of events. We discussed possible
reasons for the larger offset distribution and conclude that the
most likely explanations are:
1. The CCSNe are hosted by a diffuse stellar population
orbiting the nearby massive ellipticals. Since very few
CCSNe occur in elliptical galaxies, a small population of
CCSNe hosted by diffuse star-forming satellites would
stand out. This is supported by the 1:3 ratio of highly
offset CCSNe near spirals compared to elliptical galaxies
—in agreement with ratio of massive spirals and
ellipticals in the Galaxy Zoo sample.
2. The CCSNe originate from the nearby massive elliptical
galaxy; either from faint peripheral spiral features, or due
to extended galaxy-scale star formation due to gas
accretion from the IGM.
Finally, we derived the fraction of CCSNe occurring in
elliptical galaxies out of the general CCSN population and find
it to be -+0.4 %0.30.5 for SNe with a host galaxy associated with
them, and -+0.3 %0.10.3 when including hostless SNe. This is in
slight tension (∼ 2σ) with the fraction of star formation in
morphologically classified ellipticals satisfying the same color
criteria and calculated using traditional tracers (found to be
1± 0.01%). However, this might be explained by systematics
in the calibration of SFR relations in elliptical galaxies due to
UV emission from old stellar populations, or due to selection
effects biasing the galaxy sample in the low end of the galaxy
mass distribution. We conclude that CCSNe can be useful as
direct tracers of star formation in low sSFR environments, but
caution that proper care must be taken to avoid contamination
of both the SN sample (by misclassified SNe Ia) and the host
sample (by star-forming galaxies).
A.G.Y.’s research is supported by the EU via ERC grant
No. 725161, the ISF GW excellence center, an IMOS space
infrastructure grant, and BSF/Transformative and GIF grants,
as well as The Benoziyo Endowment Fund for the Advance-
ment of Science, the Deloro Institute for Advanced Research
in Space and Optics, The Veronika A. Rabl Physics
Discretionary Fund, Minerva, Yeda-Sela and the Schwartz/
Reisman Collaborative Science Program; A.G.Y. is the
incumbent of The Arlyn Imberman Professorial Chair. NLS
is funded by the Deutsche Forschungsgemeinschaft (DFG,
German Research Foundation) via the Walter Benjamin
program461903330. This research has made use of the
NASA/IPAC Extragalactic Database (NED), which is
operated by the Jet Propulsion Laboratory, California Institute
of Technology, under contract with the National Aeronautics
and Space Administration (NASA). Foscgui is a graphic user
interface aimed at extracting SN spectroscopy and photometry
obtained with FOSC-like instruments. It was developed by E.
Cappellaro. A package description can be found at http://
sngroup.oapd.inaf.it/foscgui.html. This work is based on
observations obtained with the Samuel Oschin Telescope 48
inch and the 60 inch Telescope at the Palomar Observatory as
part of the Zwicky Transient Facility project. ZTF is
supported by the National Science Foundation under Grant
No. AST-1440341 and a collaboration including Caltech,
IPAC, the Weizmann Institute for Science, the Oskar Klein
Center at Stockholm University, the University of Maryland,
the University of Washington, Deutsches Elektronen-Syn-
chrotron and Humboldt University, Los Alamos National
Laboratories, the TANGO Consortium of Taiwan, the
University of Wisconsin at Milwaukee, and Lawrence
Berkeley National Laboratories. Operations are conducted
by COO, IPAC, and UW. Based on observations from the Las
Cumbres Observatory network. The LCO team is supported
by NSF grants AST-1911225 and AST-1911151 The Liver-
pool Telescope is operated on the island of La Palma by
Liverpool John Moores University in the Spanish Observa-
torio del Roque de los Muchachos of the Instituto de
Astrofisica de Canarias with financial support from the UK
Science and Technology Facilities Council. Partly based on
observations made with the Nordic Optical Telescope,
operated at the Observatorio del Roque de los Muchachos,
La Palma, Spain, of the Instituto de Astrofísica de Canarias.
The SED Machine is based upon work supported by the
National Science Foundation under grant No. 1106171. The
ZTF forced-photometry service was funded under the
Heising-Simons Foundation grant #12540303 (PI: Graham).
The Legacy Surveys consist of three individual and
complementary projects: the Dark Energy Camera Legacy
Survey (DECaLS; Proposal ID #2014B-0404; PIs: David
Schlegel and Arjun Dey), the Beijing-Arizona Sky Survey
(BASS; NOAO Prop. ID #2015A-0801; PIs: Zhou Xu and
Xiaohui Fan), and the Mayall z-band Legacy Survey (MzLS;
Prop. ID #2016A-0453; PI: Arjun Dey). DECaLS, BASS and
MzLS together include data obtained, respectively, at the
Blanco telescope, Cerro Tololo Inter-American Observatory,
NSF’s NOIRLab; the Bok telescope, Steward Observatory,
University of Arizona; and the Mayall telescope, Kitt Peak
National Observatory, NOIRLab. The Legacy Surveys project
is honored to be permitted to conduct astronomical research
on Iolkam Du’ag (Kitt Peak), a mountain with particular
significance to the Tohono O’odham Nation. BASS is a key
project of the Telescope Access Program (TAP), which has
been funded by the National Astronomical Observatories of
China, the Chinese Academy of Sciences (the Strategic
Priority Research Program The Emergence of Cosmological
Structures Grant # XDB09000000), and the Special Fund for
Astronomy from the Ministry of Finance. The BASS is also
supported by the External Cooperation Program of Chinese
Academy of Sciences (Grant # 114A11KYSB20160057),
and Chinese National Natural Science Foundation (Grant #
11433005) This project has made use of data products from
the Near-Earth Object Wide-field Infrared Survey Explorer
(NEOWISE), which is a project of the Jet Propulsion
Laboratory/California Institute of Technology. NEOWISE
is funded by the National Aeronautics and Space Adminis-
tration. Based on observations collected at the European
Organisation for Astronomical Research in the Southern
Hemisphere, Chile, as part of ePESSTO/ePESSTO+ (the
extended Public ESO Spectroscopic Survey for Transient
Objects Survey) under ESO programmes 199.D-0143,1103.
D-0328,106.216C.001/007,106.216C.002/008& 106.216C.
003/009. This research has made use of the VizieR catalog
access tool, CDS, Strasbourg, France (DOI:10.26093/cds/
vizier). The original description of the VizieR service was
published in 2000, A&AS 143, 23 This work has made use of
19
The Astrophysical Journal, 927:10 (22pp), 2022 March 1 Irani et al.
data from the Asteroid Terrestrial-impact Last Alert System
(ATLAS) project. ATLAS is primarily funded to search for
near Earth asteroids through NASA grants NN12AR55G,
80NSSC18K0284, and 80NSSC18K1575; by products of the
NEO search include images and catalogs from the survey
area. The ATLAS science products have been made possible
through the contributions of the University of Hawaii Institute
for Astronomy, the Queen’s University Belfast, and the Space
Telescope Science Institute. TMB was funded by the
CONICYT PFCHA/DOCTORADOBECAS CHILE/2017-
72180113. MN is supported by a Royal Astronomical Society
Research Fellowship and by the European Research Council
(ERC) under the European Union’s Horizon 2020 research
and innovation program (grant agreement No. 948381 M.M.
K. acknowledges generous support from the David and
Lucille Packard Foundation. This work was supported by the
GROWTH Marshal (Kasliwal et al. 2019) developed as part
of the GROWTH (Global Relay of Observatories Watching
Transients Happen) project funded by the National Science
Foundation under grant No. 1545949. M.G. is supported by
the EU Horizon 2020 research and innovation program under
grant agreement No 101004719. L.G. acknowledges financial
support from the Spanish Ministry of Science, Innovation and
Universities (MICIU) under the 2019 Ramón y Cajal program
RYC2019-027683 and from the Spanish MICIU project
PID2020-115253GA-I00. T.-W.C. acknowledges the EU
Funding under Marie Skłodowska-Curie grant H2020-
MSCA-IF-2018-842471. E.C.K. acknowledges support from
the G.R.E.A.T research environment funded by Vetenskaps-
rådet, the Swedish Research Council, under project number
2016-06012, and support from The Wenner-Gren Founda-
tions. L.G. acknowledges financial support from the Spanish
Ministry of Science, Innovation and Universities (MICIU)
under the 2019 Ramón y Cajal program RYC2019-027683
and from the Spanish MICIU project PID2020-
115253GA-I00.
ORCID iDs
I. Irani https://orcid.org/0000-0002-7996-8780
S. J. Prentice https://orcid.org/0000-0003-0486-6242
S. Schulze https://orcid.org/0000-0001-6797-1889
A. Gal-Yam https://orcid.org/0000-0002-3653-5598
Paolo Mazzali https://orcid.org/0000-0001-6876-8284
J. Sollerman https://orcid.org/0000-0003-1546-6615
K. Taggart https://orcid.org/0000-0002-5748-4558
Kishalay De https://orcid.org/0000-0002-8989-0542
Christoffer Fremling https://orcid.org/0000-0002-
4223-103X
Daniel A. Perley https://orcid.org/0000-0001-8472-1996
Nora L. Strotjohann https://orcid.org/0000-0002-4667-6730
Mansi M. Kasliwal https://orcid.org/0000-0002-5619-4938
S. Dhawan https://orcid.org/0000-0002-2376-6979
Anastasios Tzanidakis https://orcid.org/0000-0003-
0484-3331
Daichi Hiramatsu https://orcid.org/0000-0002-1125-9187
Erik C. Kool https://orcid.org/0000-0002-7252-3877
J. P. Anderson https://orcid.org/0000-0003-0227-3451
T. E. Müller-Bravo https://orcid.org/0000-0003-3939-7167
Richard Dekany https://orcid.org/0000-0002-5884-7867
Mariusz Gromadzki https://orcid.org/0000-0002-1650-1518
Roberta Carini https://orcid.org/0000-0003-1604-2064
L. Galbany https://orcid.org/0000-0002-1296-6887
Jamison Burke https://orcid.org/0000-0003-0035-6659
Craig Pellegrino https://orcid.org/0000-0002-7472-1279
Massimo Della Valle https://orcid.org/0000-0003-
3142-5020
Michael S. Medford https://orcid.org/0000-0002-
7226-0659
Ben Rusholme https://orcid.org/0000-0001-7648-4142
D. R. Young https://orcid.org/0000-0002-1229-2499
Claudia P. Gutiérrez https://orcid.org/0000-0003-
2375-2064
Cosimo Inserra https://orcid.org/0000-0002-3968-4409
David L. Shupe https://orcid.org/0000-0003-4401-0430
Kyung Min Shin https://orcid.org/0000-0002-1486-3582
Ofer Yaron https://orcid.org/0000-0002-0301-8017
Curtis McCully https://orcid.org/0000-0001-5807-7893
Matt Nicholl https://orcid.org/0000-0002-2555-3192
Reed Riddle https://orcid.org/0000-0002-0387-370X
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