The Millennium Galaxy Catalogue: 16 < B_MGC < 24 galaxy counts and the calibration of the local galaxy luminosity function
Abstract
The Millennium Galaxy Catalogue (MGC) is a 37.5 deg^2, medium-deep, B-band imaging survey along the celestial equator, taken with the Wide Field Camera on the Isaac Newton Telescope. The survey region is contained within the regions of both the Two Degree Field Galaxy Redshift Survey (2dFGRS) and the Sloan Digital Sky Survey Early Data Release (SDSS-EDR). The survey has a uniform isophotal detection limit of 26 mag arcsec^-2 and it provides a robust, well-defined catalogue of stars and galaxies in the range 16 < B_MGC < 24 mag. Here we describe the survey strategy, the photometric and astrometric calibration, source detection and analysis, and present the galaxy number counts which connect the bright and faint galaxy populations within a single survey. We argue that these counts represent the state of the art and use them to constrain the normalisations (phi*) of a number of recent estimates of the local galaxy luminosity function. We find that the 2dFGRS, SDSS-EDR, SSRS2, Durham/UKST, ESO Slice Project, Mt Stromlo/APM, Autofib, Century Survey and NOG luminosity functions require a revision of their published phi* values by factors of 1.06, 0.71, 1.31, 1.06, 0.90, 1.59, 1.14, 0.97 and 0.98 respectively. After renormalising the galaxy luminosity functions we find a mean local b_j luminosity density of j = (1.88 +/- 0.07) x 10^8 h L_{\odot} Mpc^-3. Finally we comment that with a prior on the characteristic luminosity, L*, we can also constrain the faint-end slope, alpha, to within Delta alpha = 0.12 using the intermediate galaxy counts alone. The M*, alpha combinations of both the 2dFGRS and SDSS-EDR are in excellent agreement with our data. Using a joint 2dFGRS and SDSS-EDR prior of M*_{b_j} - 5 log h = -19.72 mag we find alpha = -1.23, phi* = 0.0158 h^3 Mpc^-3 and j = 1.94 x 10^8 h L_{\odot} Mpc^-3.Keywords
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