The Complete Spitzer Survey of Stellar Structure in Galaxies (CS4G)

Abstract

<p><em>Context.</em> The <em>Spitzer</em> Survey of Stellar Structure in Galaxies (S⁴G), together with its Early Type Galaxy (ETG) extension, stands as the most extensive dataset of deep uniform mid-infrared (mid-IR; 3.6 and 4.5 μm) imaging for a sample of 2817 nearby (<em>d</em> < 40 Mpc) galaxies. However, the velocity criterion used to select the original sample results in an additional 422 galaxies without H I detection that should have been included in the S⁴G on the basis of their optical recession velocities.<br></p><p><em>Aims.</em> In order to create a complete magnitude-, size-, and volume-limited sample of nearby galaxies, we collected 3.6 μm and <em>i</em>-band images using archival data from different surveys and complemented it with new observations for the missing galaxies. Since most, but not all, of these galaxies have a Hubble type in Hyperleda <em>T</em>_HL > 0, we denote the sample of these additional galaxies as disc galaxy (DG) extension. We present the Complete <em>Spitzer</em> Survey of Stellar Structure in Galaxies (CS⁴G), encompassing a sample of 3239 galaxies (S⁴G+ETG+DG) with consistent imaging, surface brightness profiles, photometric parameters, and revised morphological classification.<br></p><p><em>Methods.</em> Following the original strategy of the S⁴G survey, we produced masks, surface brightness profiles, and curves of growth using masked 3.6 μm and <em>i</em>-band images. From these profiles, we derived the integrated quantities, including total magnitude, stellar mass, concentration parameter, and galaxy size, converting between optical <em>i</em>-band and 3.6 μm. We also re-measured these parameters for the S⁴G and ETG to create a homogenous sample. We present new morphologically revised <em>T</em>-types, and we showcase mid-IR scaling relations for the stellar mass, galaxy size, concentration index, and morphological type.</p><p><em>Results.</em> Our new masking procedure increases the number of pixels masked out by a factor of five, improving the masking of fainter regions over previous S⁴G data. Our photometric parameters from <em>i</em>-band imaging yield measurements consistent with the original sample (S⁴G) and its ETG extension in the 3.6 μm band. The new DG extension consists of galaxies with a wide morphological range (−5 < <em>T</em>_HL < 10) and a mass range of 6 < log(<em>M</em>_⋆/<em>M</em>_⊙) < 11. The galaxies in the DG sample have an average mass of log(<em>M</em>_⋆/<em>M</em>_⊙) = 9.21, an average galaxy isophotal radius at 25.5 mag arcsec⁻² of <em>R</em>_25.5 = 7.1 kpc, and an average concentration index of <em>C</em>₈₂ = 2.92.</p><p><em>Conclusions.</em> We completed the S⁴G sample by incorporating 422 galaxies into the original dataset. The new galaxies constitute 15% of the total previous sample (S⁴G+ETG), but in the lower-mass range (<em>M</em>_⋆ < 10⁹ <em>M</em>_⊙), and the disc galaxy extension increases the sample by 36%. The CS⁴G includes at least 99.94% of the complete sample of nearby galaxies, meeting the original selection criteria based on a comparison with the NED database. We make the images and surface brightness profiles available to the community together with the conjunct catalogue of the whole CS⁴G dataset with consistent photometric measurements for 3239 galaxies. The CS⁴G will enable a wide set of investigations into galaxy structure and evolution, and it will complement the optical, near-IR, and mid-IR imaging that will obtained in the coming years with <em>Euclid</em>, <em>Rubin, Roman</em>, and other research projects.<br></p>