High-redshift narrow-line Seyfert 1 galaxies: a candidate sample

Abstract

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