The PAU Survey: The quasar UV and Ly$\hat{I}\pm$ luminosity functions at $2.7<z<5.3$

Abstract

We present the Lyman-$\hat{I}\pm$ (Ly$\hat{I}\pm$) and ultraviolet (UV) luminosity function (LF), in bins of redshift, of 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 $\sim 36$ deg${}^2$ observed in 40 narrow-band filters (NB; FWHM $\sim 120$ Ã ). We cover the intermediate-bright luminosity regime of the LF $(10^{43.5}<(L_{\mathrm{Ly}\hat{I}\pm }/{\mathrm{erg}\mathrm{s}}^{-1})<10^{45.5}$; $-29<M_{\mathrm{UV}}<-24)$. The continuous wavelength coverage of the PAUS NB set allows a very efficient target identification and precise redshift measurements. We show that our method is able to retrieve a fairly complete ($C\sim 85\%$) and pure ($P\sim 90\%$) sample of Ly$\hat{I}\pm$ emitting quasars for $L_{\mathrm{Ly}\hat{I}\pm }>10^{44}$ $\mathrm{erg}\mathrm{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 Ly$\hat{I}\pm$ and UV LFs, with a declining tendency in the number density of quasars towards increasing redshifts. In addition, the faint-end power-law slope of the Ly$\hat{I}\pm$ LF becomes steeper with redshift, suggesting that the number density of Ly$\hat{I}\pm$-bright quasars declines faster than that of fainter emitters. By integrating the Ly$\hat{I}\pm$ LF we find that the total Ly$\hat{I}\pm$ emitted by bright quasars per unit volume rapidly declines with increasing redshift, being sub-dominant to that of star-forming galaxies by several orders of magnitude by $z\sim 4$. 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 to measure the mean IGM absorption by the Lyman-$\hat{I}\pm$ forest as a function of redshift.

17 pages, 16 figures. Submitted to A&A. Relevant figs: 7 (Ly-alpha LF), 10 (UV LF). Accepted in A&A