2005MNRAS.360...81D

We recover the joint and individual space density and surface-brightness distribution(s) of galaxies from the Millennium Galaxy Catalogue (MGC). The MGC is a local survey spanning 30.9 deg² and probing approximately 1-2 mag/arcsec2 deeper than either the Two-Degree Field Galaxy Redshift Survey (2dFGRS) or the Sloan Digital Sky Survey (SDSS). The MGC contains 10095 galaxies to B_MGC< 20 mag with 96 per cent spectroscopic completeness. For each galaxy we derive individual K-corrections and seeing-corrected sizes. We implement a joint luminosity-surface-brightness step-wise maximum-likelihood method to recover the bivariate brightness distribution (BBD) inclusive of most selection effects. Integrating the BBD over surface brightness we recover the following Schechter function parameters: φ*= (0.0177±0.0015)h³/Mpc3, M*_BMGC- 5 log h= (-19.60±0.04) mag and α=-1.13±0.02. Compared to the 2dFGRS we find a consistent M* value but a slightly flatter faint-end slope and a higher normalization, resulting in a final luminosity density j_bJ= (1.99±0.17) x10⁸hL_☉/Mpc3 - marginally higher than, but consistent with, the earlier 2dFGRS, ESP, and SDSS z= 0.1 results. The MGC is inconsistent with the SDSS z= 0.0 result (+3σ) if one adopts the derived SDSS evolution.

The MGC surface-brightness distribution is a well-bounded Gaussian at the M* point with φ*= (3.5±0.1)x10^–2h³/Mpc3, µ^e*= (21.90±0.01) mag/arcsec2 and σ_ln R_e_= 0.35 ±0.01. The characteristic surface brightness for luminous systems is invariant to M_BMGC- 5 log h~-19 mag faintwards of which it moves to lower surface brightness. The surface-brightness distribution also broadens (σ_ln R_e_~ 0.5 - 0.7) towards lower luminosities. The luminosity dependence of σ_ln R_e_provides a new constraint for both the theoretical development and numerical simulations, which typically predict a mass-independent σ_lnR_e_~ 0.56±0.04.

Higher resolution (FWHM ≪ 1 arcsec) and deeper (µ_lim≫ 26 mag/arcsec2 in the B-band) observations of the local Universe are now essential to probe to lower luminosity and lower surface-brightness levels.