Gamma-Ray-emitting Narrow-line Seyfert 1 Galaxies in the Sloan Digital Sky Survey

Abstract

The detection of signi fi cant γ -ray emission from radio-loud narrow-line Seyfert 1 ( NLSy1s ) galaxies enables us to study jets in environments different than those in blazars. However, due to the small number of known γ -ray- emitting NLSy1 ( γ -NLSy1 ) galaxies, a comprehensive study could not be performed. Here, we report the fi rst detection of signi fi cant γ -ray emission from four active galactic nuclei ( AGNs ) , recently classi fi ed as NLSy1 from their Sloan Digital Sky Survey ( SDSS ) optical spectrum. Three fl at-spectrum radio quasars ( FSRQs ) present in the third Large Area Telescope AGN catalog ( 3LAC ) are also found as γ -NLSy1 galaxies. Comparing the γ -ray properties of these objects with 3LAC blazars reveals their spectral shapes to be similar to FSRQs, however, with low γ -ray luminosity (  10 46 – 47 erg s − 1 ) . In the Wide- fi eld Infrared Survey Explorer color – color diagram, these objects occupy a region mainly populated by FSRQs. Using the H β emission line parameters, we fi nd that on average γ -NLSy1 have smaller black hole masses than FSRQs at similar redshifts. In the low-resolution SDSS image of one of the γ -NLSy1 source, we fi nd the evidence of an extended structure. We conclude by noting that overall many observational properties of γ -NLSy1 sources are similar to FSRQs, and therefore these objects could be their low black hole mass counterparts, as predicted in the literature.