Evolution of environment dependent galaxy properties in the Sloan Digital Sky Survey

O´MILL, ANA LAURA; PADILLA, NELSON; GARCIA LAMBAS, DIEGO

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2008 vol. 389 p. 1763 - 1770

0035-8711

We use photometric redshifts to analyse the effect of local environment on galaxy colours at redshifts z <0.63 in the SDSS data release 6.  We construct mock SDSS-DR6 catalogues using semi-analytic galaxies tostudy possible systematic effects on the characterisation of environment andcolour statistics due to the uncertainty in the determination of redshifts.We use the projected galaxy density derived from the distance to the nearest neighbourswith a suitable radial velocity threshold to take into account the uncertainties in the photometric redshift estimates.Our findings indicate that the use of photometric redshifts greatly improves estimates of projected local galaxy density when galaxy spectra are not available.  We find a tight relationship betweenspectroscopic and photometric derived densities, both in the SDSS-DR6 data (up to z=0.3) and mock catalogues (up to z=0.63).At z=0, faint galaxies show a clear increase of the red galaxy fraction asthe local density increases.  Bright galaxies, on the other hand, show a constantred galaxy fraction.  We are able to trackthe evolution of this fraction to z=0.55 for galaxies brighter thanM_r=-21.5 and find that the fraction of blue galaxies with respect to thetotal population progressively becomes higheras the redshift increases, at a rate of 15 %/Gyr.  Also, at any given redshift, bright galaxies show a larger red population, indicating that the star-formation activity shifts towardssmaller objects as the redshift decreases.