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

TL;DR

This study investigates how local environment influences galaxy colors over time using SDSS data and mock catalogues, revealing that galaxy color fractions evolve with redshift and depend on galaxy brightness.

Contribution

It introduces a method to accurately estimate local galaxy density using photometric redshifts and tracks the evolution of galaxy color fractions up to redshift 0.55.

Findings

Photometric redshifts improve local density estimates.

Red galaxy fraction increases with density at z=0.

Blue galaxy fraction rises with redshift for bright galaxies.

Abstract

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 to study possible systematic effects on the characterisation of environment and colour statistics due to the uncertainty in the determination of redshifts. We use the projected galaxy density derived from the distance to the nearest neighbours with 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 between spectroscopic 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 as the local density increases. Bright galaxies, on the other hand, show a constant red galaxy fraction. We are able to track the evolution of this fraction to z=0.55 for galaxies brighter than M_r=-21.5 and find that the fraction of blue galaxies with respect to the total population progressively becomes higher as 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 towards smaller objects as the redshift decreases.