First HETDEX Spectroscopic Determinations of Lyα and UV Luminosity Functions at z=2−3: Bridging a Gap Between Faint AGN and Bright Galaxies

We present Lyα and ultraviolet-continuum (UV) luminosity functions (LFs) of galaxies and active galactic nuclei (AGN) at z=2.0−3.5 determined by the un-targetted 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 18320 galaxies spectroscopically identified with Lyα emission, 2126 of which host type 1 AGN 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 AGN in logLLyα/[erg s−1]=43.3−45.2 (−27<MUV<−20) by the 1/Vmax estimator. Our results reveal the bright-end hump of the Lyα LF is composed of type 1 AGN. In conjunction with previous spectroscopic results at the faint end, we measure a slope of the best-fit Schechter function to be αSch=−1.70+0.13−0.14, which indicates αSch steepens from z=2−3 towards 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 (XLAE) increases from M∗UV∼−21 to bright magnitude due to the contribution of type 1 AGN, while previous studies claim that XLyα decreases from faint magnitude to M∗UV, suggesting a valley in the XLyα−magnitude relation at M∗UV. Comparing our UV LF of type 1 AGN at z=2−3 with those at z=0, we find that the number density of faint (MUV>−21) type 1 AGN increases from z∼2 to z∼0 as opposed to the evolution of bright (MUV<−21) type 1 AGN, suggesting the AGN downsizing in the rest-frame UV luminosity.

First HETDEX Spectroscopic Determinations of Lyα and UV Luminosity Functions at z=2−3: Bridging a Gap Between Faint AGN and Bright Galaxies, Yechi ZhangMasami OuchiKarl GebhardtErin Mentuch CooperChenxu LiuDustin DavisDonghui JeongDaniel J. FarrowSteven L. FinkelsteinEric GawiserGary J. HillRyota KakumaViviana AcquavivaCaitlin M. CaseyMaximilian FabriciusUlrich HoppMatt J. JarvisMartin LandriauKen MawatariShiro MukaeYoshiaki OnoNao SakaiDonald P. Schneider, arXiv:2105.11497, submitted to ApJ