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

Zhang, Yechi; Ouchi, Masami; Gebhardt, Karl; Cooper, Erin Mentuch; 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 und Schneider, Donald P. (2021): First HETDEX Spectroscopic Determinations of Ly alpha and UV Luminosity Functions at z=2-3: Bridging a Gap between Faint AGNs and Bright Galaxies. In: Astrophysical Journal, Bd. 922, Nr. 2, 167

Abstract

We present Ly alpha 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 deg(2) of fiber spectra sky coverage, obtaining 18,320 galaxies spectroscopically identified with Ly alpha emission, 2126 of which host type 1 AGNs showing broad (FWHM > 1000 km s(-1)) Ly alpha emission lines. We derive the Ly alpha (UV) LF over 2 orders of magnitude covering bright galaxies and AGNs in log(LLy alpha)/[ergs(-1)]=43.3-45.5 <i (-27 < M-UV < -20) by the 1/V-max estimator. Our results reveal that the bright-end hump of the Ly alpha 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 Sch=-1.70(-0.14)(+0.13), which indicates that alpha (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 Ly alpha-emitting objects (X (LAE)) increases from M-UV*similar to-21 <i to bright magnitude due to the contribution of type 1 AGNs, while previous studies claim that X (Ly alpha) decreases from faint magnitudes to M-UV* <i , suggesting a valley in the X (Ly alpha) -magnitude relation at MUV* 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 similar to 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.

• Dokumententyp: Zeitschriftenartikel
• Fakultät: Physik
• Themengebiete: 500 Naturwissenschaften und Mathematik > 530 Physik
• ISSN: 0004-637X
• Sprache: Englisch