Quasar UV Luminosity Function at $3.5<z<5.0$ from SDSS Deep Imaging Data

TL;DR

This study constructs the UV luminosity function of quasars at redshifts 3.5 to 5 using SDSS data, revealing the evolution of quasar density and luminosity distribution during this epoch.

Contribution

It provides a large, deep quasar sample extending previous surveys and models the luminosity function with improved constraints across a wide luminosity range.

Findings

Faint-end slope around -1.7

Bright-end slope around -3.7

Quasar density evolution is nearly uniform from z=3.5 to 7

Abstract

We present a well-designed sample of more than 1000 type 1 quasars at $3.5<z<5$ and derive UV quasar luminosity functions (QLFs) in this redshift range. These quasars were selected using the Sloan Digital Sky Survey (SDSS) imaging data in SDSS Stripe 82 and overlap regions with repeat imaging observations. They are about one magnitude fainter than those found using the SDSS single-epoch data. The spectroscopic observations were conducted by the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS) as one of the BOSS ancillary programs. This quasar sample reaches $i\sim21.5$ mag and bridges previous samples from brighter surveys and deeper surveys. We use a $1/V_\mathrm{a}$ method to derive binned QLFs at $3.6<z<4.0$, $4.0<z<4.5$, and $4.5<z<4.9$, and use a double-power law model to parameterize the QLFs. We also combine our data with those in the literature to better constrain the QLFs in the context of a much wider luminosity baseline. We find that the faint-end and bright-end slopes of the QLFs in this redshift range are around $-1.7$ and $-3.7$, respectively, with uncertainties from 0.2$-$0.3 to $>0.5$. The evolution of the QLFs from $z\sim5$ to $3.5$ can be described by a pure density evolution model ($\propto10^{kz}$) and the parameter $k$ is similar to that at $5<z<7$, suggesting a nearly uniform evolution of the quasar density at $z=3.5-7$.