First HETDEX Spectroscopic Determinations of Lyα and UV Luminosity Functions at z = 2-3: Bridging a Gap between Faint AGNs and Bright Galaxies

December 2021 • 2021ApJ...922..167Z

Authors • Zhang, Yechi • Ouchi, Masami • Gebhardt, Karl • Mentuch Cooper, Erin • Liu, Chenxu • Davis, Dustin • Jeong, Donghui • Farrow, Daniel J. • Finkelstein, Steven L. • Gawiser, Eric • Hill, Gary J. • Harikane, Yuichi • Kakuma, Ryota • Acquaviva, Viviana • Casey, Caitlin M. • Fabricius, Maximilian • Hopp, Ulrich • Jarvis, Matt J. • Landriau, Martin • Mawatari, Ken • Mukae, Shiro • Ono, Yoshiaki • Sakai, Nao • Schneider, Donald P.

Abstract • We present Lyα and ultraviolet (UV)-continuum luminosity functions (LFs) of galaxies and active galactic nuclei (AGNs) at z = 2.0-3.5 determined by the untargeted optical spectroscopic survey of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). We combine deep Subaru imaging with HETDEX spectra resulting in 11.4 deg² of fiber spectra sky coverage, obtaining 18,320 galaxies spectroscopically identified with Lyα emission, 2126 of which host type 1 AGNs showing broad (FWHM > 1000 km s^-1) Lyα emission lines. We derive the Lyα (UV) LF over 2 orders of magnitude covering bright galaxies and AGNs in $\mathrm{log}{L}_{\mathrm{Ly}\alpha }/[\mathrm{erg}\,{{\rm{s}}}^{-1}]=43.3\mbox{--}45.5> (-27 < M _UV < -20) by the 1/V _max estimator. Our results reveal that the bright-end hump of the Lyα LF is composed of type 1 AGNs. In conjunction with previous spectroscopic results at the faint end, we measure a slope of the best-fit Schechter function to be ${\alpha }_{\mathrm{Sch}}=-{1.70}_{-0.14}^{+0.13}> , which indicates that α _Sch steepens from z = 2-3 toward high redshift. Our UV LF agrees well with previous AGN UV LFs and extends to faint-AGN and bright-galaxy regimes. The number fraction of Lyα-emitting objects (X _LAE) increases from ${M}_{\mathrm{UV}}^{* }\sim -21> to bright magnitude due to the contribution of type 1 AGNs, while previous studies claim that X _Lyα decreases from faint magnitudes to ${M}_{\mathrm{UV}}^{* }> , suggesting a valley in the X _Lyα -magnitude relation at ${M}_{\mathrm{UV}}^{* }> . Comparing our UV LF of type 1 AGNs at z = 2-3 with those at z = 0, we find that the number density of faint (M _UV > -21) type 1 AGNs increases from z ~ 2 to 0, as opposed to the evolution of bright (M _UV < -21) type 1 AGNs, suggesting AGN downsizing in the rest-frame UV luminosity.

Links

• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2021ApJ...922..167Z
• PREPRINT http://arxiv.org/abs/2105.11497
• DATA https://archive.stsci.edu/mastbibref.php?bibcode=2021ApJ...922..167Z
• DATA https://hst.esac.esa.int/ehst/#/pages/search;bibcode=2021ApJ...922..167Z
• DATA https://irsa.ipac.caltech.edu/bibdata/2021/Z/2021ApJ...922..167Z.html
• ELECTR https://doi.org/10.3847%2F1538-4357%2Fac1e97