The SDSS DR6 Luminosity Functions of Galaxies

TL;DR

This paper presents detailed galaxy luminosity functions from SDSS DR6, revealing a bright-end excess mainly from active galaxies and QSOs, and providing more accurate faint-end measurements than previous studies.

Contribution

The study offers the first high-precision SDSS DR6 luminosity functions across all bands, with improved statistics, redshift completeness, and insights into bright-end excess origins.

Findings

Bright-end excess in u-band mainly from active galaxies and QSOs.

Steeper faint-end slope than previous SDSS estimates.

High redshift completeness and improved statistical accuracy.

Abstract

We present number counts, luminosity functions (LFs) and luminosity densities of galaxies obtained using the Sloan Digital Sky Survey Sixth Data Release in all SDSS photometric bands. Thanks to the SDSS DR6, galaxy statistics have increased by a factor of ~9 in the u-band and by a factor of ~4-5 in the rest of the SDSS bands with respect to the previous work of Blanton et al. (2003b). In addition, we have achieved a high redshift completeness in our galaxy samples. Firstly, by making use of the survey masks, provided by the NYU-VAGC DR6, we have been able to define an area on the sky of high angular redshift completeness. Secondly, we guarantee that brightness-dependent redshift incompleteness is small within the magnitude ranges that define our galaxy samples. With these advances, we have estimated very accurate SDSS DR6 LFs in both the bright and the faint end. In the {0.1}^r-band, our SDSS DR6 luminosity function is well fitted by a Schechter LF with parameters Phi_{*}=0.90 +/- 0.07$, M_{*}-5log_{10}h=-20.73 +/- 0.04 and alpha=-1.23 +/- 0.02. As compared with previous results, we find some notable differences. In the bright end of the {0.1}^u-band luminosity function we find a remarkable excess, of ~1.7 dex at M_{{0.1}^u}=-20.5, with respect to the best-fit Schechter LF. This excess weakens in the {0.1}^g-band, fading away towards the very red {0.1}^z-band. A preliminary analysis on the nature of this bright-end bump reveals that it is mostly comprised of active galaxies and QSOs. It seems, therefore, that an important fraction of this exceeding luminosity may come from nuclear activity. In the faint end of the SDSS DR6 luminosity functions, where we can reach 1-1.5 magnitudes deeper than the previous SDSS LF estimation, we obtain a steeper slope [ABRIDGED].