High-redshift Narrow-line Seyfert 1 Galaxies: A Candidate Sample

Abstract

<div>The study of narrow-line Seyfert 1 galaxies (NLS1s) is now mostly limited to low redshift (<i>z</i> < 0.8) because their definition requires the presence of the H<i>β</i> emission line, which is redshifted out of the spectral coverage of major ground-based spectroscopic surveys at <i>z</i> > 0.8. We studied the correlation between the properties of H<i>β</i> and Mg ii lines of a large sample of SDSS DR14 quasars to find high-<i>z</i> NLS1 candidates. Based on the strong correlation of FWHM(Mg II) = (0.880 ± 0.005) <b>×</b> FWHM(H<i>β</i>) + (0.438 ± 0.018), we present a sample of high-<i>z</i> NLS1 candidates having FWHM of Mg ii < 2000 km s⁻¹. The high-<i>z</i> sample contains 2684 NLS1s with redshift <i>z</i> = 0.8–2.5 with a median logarithmic bolometric luminosity of 46.16 ± 0.42 erg s⁻¹, logarithmic black hole mass of 8.01 ± 0.35 <i>M</i>_⊙, and logarithmic Eddington ratio of 0.02 ± 0.27. The fraction of radio-detected high-<i>z</i> NLS1s is similar to that of the low-<i>z</i> NLS1s and SDSS DR14 quasars at a similar redshift range, and their radio luminosity is found to be strongly correlated with their black hole mass.</div>