Abstract

We present number counts, luminosity functions (LFs) and luminosity densities of galaxies obtained using the Sloan Digital Sky Survey Sixth Data Release (SDSS DR6) in all SDSS photometric bands. Thanks to the SDSS DR6, galaxy statistics have increased by a factor of similar to 7 in the u band and by a factor between similar to 3 and similar to 5 in the rest of the SDSS bands with respect to the previous work of Blanton et al. In addition, we have ensured a high redshift completeness in our galaxy samples, mainly by minimizing the effect of brightness-dependent incompleteness. With these advances, we have estimated very accurate SDSS DR6 LFs at both the bright and the faint end. In the 0.1r band, our LF is well fitted by a Schechter LF with parameters (*) = 0.93 +/- 0.07, M-* - 5log(10) h = -20.71 +/- 0.04 and alpha = -1.26 +/- 0.02. As compared with previous results, we find some notable differences. At the bright end of the 0.1u-band LF we find a remarkable excess, of similar to 1.7 dex M0.1(u) similar or equal to -20.5, with respect to the best-fitting Schechter LF. This excess weakens in the 0.1g band, fading away towards the very red 0.1z band. A preliminary analysis on the nature of this bright-end bump reveals that it is composed of quasi-stellar objects/type 1 Seyferts (similar to 60 per cent), starbursts and star-forming galaxies (similar to 20 per cent) and normal galaxies (similar to 20 per cent). It seems, therefore, that an important fraction of this excess luminosity may come from nuclear activity. At the faint end of the SDSS DR6 LFs, where we can reach 0.5-1 mag deeper than the previous SDSS LF estimations, we obtain a steeper slope that increases from the 0.1u band, with alpha = -1.05 +/- 0.05, to the very red 0.1z band, with alpha = -1.26 +/- 0.03. We have also investigated the effect of galaxy evolution on our LFs. These state-of-the-art results may be used to constrain a variety of aspects of star formation histories and/or feedback processes in galaxy formation models.