The Extremely Luminous Quasar Survey in the Sloan Digital Sky Survey footprint. III. The South Galactic Cap Sample and the Quasar Luminosity Function at Cosmic Noon

Abstract

We have designed the Extremely Luminous Quasar Survey (ELQS) to provide a highly complete census of unobscured UV-bright quasars during the cosmic noon, $z=2.8-5.0$. Here we report the discovery of 70 new quasars in the ELQS South Galactic Cap (ELQS-S) quasar sample, doubling the number of known extremely luminous quasars in $4,237.3{\mathrm{deg}}^2$ of the SDSS footprint. These observations conclude the ELQS and we present the properties of the full ELQS quasar catalog, containing 407 quasars over $11,838.5{\mathrm{deg}}^2$. Our novel ELQS quasar selection strategy resulted in unprecedented completeness at the bright end and allowed us to discover 109 new quasars in total. This marks an increase of $\sim 36\%$ (109/298) to the known population at these redshifts and magnitudes, while we further are able to retain a selection efficiency of $\sim 80\%$. On the basis of 166 quasars from the full ELQS quasar catalog, who adhere to the uniform criteria of the 2MASS point source catalog, we measure the bright-end quasar luminosity function (QLF) and extend it one magnitude brighter than previous studies. Assuming a single power law with exponential density evolution for the functional form of the QLF, we retrieve the best fit parameters from a maximum likelihood analysis. We find a steep bright-end slope of $\beta \approx -4.1$ and we can constrain the bright-end slope to $\beta \le -3.4$ with $99\%$ confidence. The density is well modeled by the exponential redshift evolution, resulting in a moderate decrease with redshift ($\gamma \approx -0.4$).

30 pages, 11 figures, ApJ accepted

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• Ultra-luminous quasars at redshift $z>4.5$ from SkyMapper
• Spectroscopy of QUBRICS quasar candidates: 1672 new redshifts and a Golden Sample for the Sandage Test of the Redshift Drift
• The Probabilistic Random Forest applied to the selection of quasar candidates in the QUBRICS Survey
• Pure Density Evolution of the Ultraviolet Quasar Luminosity Function at $2\lesssim z\lesssim 6$
• Ionizing radiation from AGNs at z>3.3 with the Subaru Hyper Suprime-Cam Survey and the CFHT Large Area U-band Deep Survey (CLAUDS)
• Forecasting cosmic acceleration measurements using the Lyman-$\alpha$ forest
• Quasar UV Luminosity Function at $3.5<z<5.0$ from SDSS Deep Imaging Data
• Eddington accreting Black Holes in the Epoch of Reionization
• Spritz is sparkling: simulated CO and [CII] luminosities
• A Closer Look at Two of the Most Luminous Quasars in the Universe
• The probabilistic random forest applied to the QUBRICS survey: improving the selection of high-redshift quasars with synthetic data
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