The PAU Survey: The quasar Lyα and UV luminosity functions at 2.7 < z < 5.3

¹ Observatori Astronòmic de la Universitat de València, Ed. Instituts d’Investigació, Parc Científic, C/ Catedrático José Beltrán, n2, 46980 Paterna, Valencia, Spain
² Departament d’Astronomia i Astrofísica, Universitat de València, 46100 Burjassot, Spain
³ Department of Astronomy, Tsinghua University, Beijing 100084, China
⁴ Instituto de Física de Cantabria (CSIC-UC), Avda. Los Castros s/n, 39005 Santander, Spain
⁵ Unidad Asociada “Grupo de Astrofísica Extragaláctica y Cosmología”, IFCA-CSIC/Universitat de València, València, Spain
⁶ Institute of Cosmology and Gravitation (University of Portsmouth), Portsmouth, UK
⁷ Institute of Space Sciences (ICE, CSIC), E-08193 Barcelona, Spain
⁸ Institut d’Estudis Espacials de Catalunya (IEEC), Edifici RDIT, Campus UPC, 08860 Castelldefels, Barcelona, Spain
⁹ Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Avenida Complutense 40, E-28040 Madrid, Spain
¹⁰ Port d’Informació Científica (PIC), Campus UAB, C. Albareda s/n, 08193 Bellaterra, Barcelona, Spain
¹¹ Institut de Física d’Altes Energies (IFAE), The Barcelona Institute of Science and Technology, Campus UAB, 08193 Bellaterra, Barcelona, Spain
¹² Instituto de Fisica Teorica (UAM/CSIC), Nicolas Cabrera 13, E-28049 Madrid, Spain
¹³ Ruhr University Bochum, Faculty of Physics and Astronomy, Astronomical Institute (AIRUB), German Centre for Cosmological Lensing, 44780 Bochum, Germany
¹⁴ Leiden Observatory, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands
¹⁵ Institució Catalana de Recerca i Estudis Avançats (ICREA), 0810 Barcelona, Spain

^⋆ Corresponding authors; alberto.torralba@uv.es, p.renard.guiral@gmail.com

Received: 26 July 2024
Accepted: 6 September 2024

Abstract

We present the Lyman-α (Lyα) and ultraviolet (UV) luminosity function (LF) in bins of redshift for quasars selected in the Physics of the Accelerating Universe Survey (PAUS). A sample of 915 objects was selected at 2.7 < z < 5.3 within an effective area of ∼36 deg² observed in 40 narrow-band (NB) filters (FWHM ∼ 120 Å). We cover the intermediate–bright luminosity regime of the LF (${10}^{43.5}<(L_{\mathrm{Ly}\alpha }/{\mathrm{erg}\mathrm{s}}^{-1})<{10}^{45.5}$; −29 < M_UV < −24). The continuous wavelength coverage of the PAUS NB set allows very efficient target identification and precise redshift measurements. We show that our method is able to retrieve a relatively complete (C ∼ 85%) and pure (P ∼ 90%) sample of Lyα-emitting quasars for L_Lyα > 10⁴⁴ erg s⁻¹. In order to obtain corrections for the LF estimation, and assess the accuracy of our selection method, we produced mock catalogs of 0 < z < 4.3 quasars and galaxies that mimic our target population and their main contaminants. Our results show a clear evolution of the Lyα and UV LFs, with a declining tendency in the number density of quasars toward increasing redshifts. In addition, the faint-end power-law slope of the Lyα LF becomes steeper with redshift, suggesting that the number density of Lyα-bright quasars declines faster than that of fainter emitters. By integrating the Lyα LF, we find that the total Lyα emitted by bright quasars per unit volume rapidly declines with increasing redshift, being subdominant to that of star-forming galaxies by several orders of magnitude by z ∼ 4. Finally, we stack the NB pseudo-spectra of a visually selected “golden sample” of 591 quasars to obtain photometric composite SEDs in bins of redshift, enabling us to measure the mean intergalactic medium absorption using the Lyman-α forest as a function of redshift, yielding results consistent with previous spectroscopic determinations.