First HETDEX Spectroscopic Determinations of Lyα and UV Luminosity Functions at z = 2–3: Bridging a Gap between Faint AGNs and Bright Galaxies
Yechi Zhang, Masami Ouchi, Karl Gebhardt, Erin Mentuch Cooper, Chenxu Liu, Dustin Davis, Donghui Jeong, Daniel J. Farrow, Steven L. Finkelstein, Eric Gawiser, Gary J. Hill, Yuichi Harikane, Ryota Kakuma, Viviana Acquaviva, Caitlin M. Casey, Maximilian Fabricius, U. Hopp, M. J. Jarvis, Martin Landriau, Ken Mawatari, Shiro Mukae, Yoshiaki Ono, Nao Sakai, Donald P. Schneider
Abstract
Abstract We present Ly α 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 α emission, 2126 of which host type 1 AGNs showing broad (FWHM > 1000 km s −1 ) Ly α emission lines. We derive the Ly α (UV) LF over 2 orders of magnitude covering bright galaxies and AGNs in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msub> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>Ly</mml:mi> <mml:mi>α</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mo stretchy="false">[</mml:mo> <mml:mi>erg</mml:mi> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> <mml:mo stretchy="false">]</mml:mo> <mml:mo>=</mml:mo> <mml:mn>43.3</mml:mn> <mml:mo>–</mml:mo> <mml:mn>45.5</mml:mn> </mml:math> (−27 < M UV < −20) by the 1/ V max estimator. Our results reveal that the bright-end hump of the Ly α 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>α</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>Sch</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>1.70</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.14</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.13</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> , 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 Ly α -emitting objects ( X LAE ) increases from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>UV</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msubsup> <mml:mo>∼</mml:mo> <mml:mo>−</mml:mo> <mml:mn>21</mml:mn> </mml:math> to bright magnitude due to the contribution of type 1 AGNs, while previous studies claim that X Ly α decreases from faint magnitudes to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>UV</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> , suggesting a valley in the X Ly α –magnitude relation at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>UV</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> . 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.