The DEEP2 Galaxy Redshift Survey: Environments of Poststarburst Galaxies at z~0.1 and z~0.8

TL;DR

This study compares the environments of poststarburst galaxies at two different redshifts, revealing a shift from underdense to more overdense environments over time, and highlights the importance of robust statistical methods in environmental analysis.

Contribution

It provides a comparative analysis of K+A galaxy environments at z~0.1 and z~0.8 using a robust selection method and introduces improved statistical approaches for studying galaxy environment relations.

Findings

K+A galaxies at low-z prefer underdense environments, similar to blue galaxies.

At high-z, K+A galaxies are found in environments more similar to red galaxies.

The environment of K+A galaxies evolves from underdense to more overdense with increasing redshift.

Abstract

Postststarburst (K+A) galaxies are candidates for galaxies in transition from a star-forming phase to a passively-evolving phase. We have spectroscopically identified large samples of K+A galaxies both in the SDSS at z~0.1 and in the DEEP2 survey at z~0.8, using a robust selection method based on a cut in Hbeta emission rather than the more problematic [OII] 3727. Based on measurements of the overdensity of galaxies around each object, we find that K+A galaxies brighter than 0.4L*_B at low-z have a similar, statistically indistinguishable environment distribution as blue galaxies, preferring underdense environments, but dramatically different from that of red galaxies. However, at higher-z, the environment distribution of K+A galaxies is more similar to red galaxies than to blue galaxies. We conclude that the quenching of star formation and the build-up of the red sequence through the K+A phase is happening in relatively overdense environments at z~1 but in relatively underdense environments at z~0. Although the relative environments where quenching occurs are decreasing with time, the corresponding absolute environment may have stayed the same along with the quenching mechanisms, because the mean absolute environments of all galaxies has to grow with time. In addition, we do not find any significant dependence on luminosity in the environment distribution of K+As. The existence of a large K+A population in the field at both redshifts indicates that cluster-specific mechanisms cannot be the dominant route by which these galaxies are formed. We also demonstrates that studying K+A-environment relations by measuring the K+A fraction in different environments is highly non-robust. Statistical comparisons of the overall environment distributions of different populations are much better behaved.