Galaxy and mass assembly (gama): Colour- and luminosity-dependent clustering from calibrated photometric redshifts

Abstract

We measure the two-point angular correlation function of a sample of 4289223 galaxies with r < 19.4mag from the Sloan Digital Sky Survey (SDSS) as a function of photometric redshift, absolute magnitude and colour down to Mr - 5logh = -14mag. Photometric redshifts are estimated from ugriz model magnitudes and two Petrosian radii using the artificial neural network package annz, taking advantage of the Galaxy And Mass Assembly (GAMA) spectroscopic sample as our training set. These photometric redshifts are then used to determine absolute magnitudes and colours. For all our samples, we estimate the underlying redshift and absolute magnitude distributions using Monte Carlo resampling. These redshift distributions are used in Limber's equation to obtain spatial correlation function parameters from power-law fits to the angular correlation function. We confirm an increase in clustering strength for sub-L red galaxies compared with ∼L red galaxies at small scales in all redshift bins, whereas for the blue population the correlation length is almost independent of luminosity for ∼L galaxies and fainter. A linear relation between relative bias and log luminosity is found to hold down to luminosities L ∼ 0.03L. We find that the redshift dependence of the bias of the L population can be described by the passive evolution model of Tegmark & Peebles. A visual inspection of a random sample from our r < 19.4 sample of SDSS galaxies reveals that about 10per cent are spurious, with a higher contamination rate towards very faint absolute magnitudes due to over-deblended nearby galaxies. We correct for this contamination in our clustering analysis. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.