The Environmental Dependence of the Evolving S0 Fraction

TL;DR

This study investigates how the increase in S0 galaxy fractions over time depends on galaxy environment, finding that galaxy-galaxy interactions in low-sigma groups are a key driver of morphological transformation.

Contribution

It reveals that the rise in S0 galaxies is more pronounced in low-sigma environments, emphasizing the role of galaxy-galaxy interactions over other environmental processes.

Findings

Stronger f_S0 evolution in low-sigma groups

Galaxy interactions dominate S0 formation in low-sigma environments

Rapid S0 growth indicates many progenitors at z ~ 0.5

Abstract

We reinvestigate the dramatic rise in the S0 fraction, f_S0, within clusters since z ~ 0.5. In particular, we focus on the role of the global galaxy environment on f_S0 by compiling, either from our own observations or the literature, robust line-of-sight velocity dispersions, sigma's, for a sample of galaxy groups and clusters at 0.1 < z < 0.8 that have uniformly determined, published morphological fractions. We find that the trend of f_S0 with redshift is twice as strong for sigma < 750 km/s groups/poor clusters than for higher-sigma, rich clusters. From this result, we infer that over this redshift range galaxy-galaxy interactions, which are more effective in lower-sigma environments, are more responsible for transforming spiral galaxies into S0's than galaxy-environment processes, which are more effective in higher-sigma environments. The rapid, recent growth of the S0 population in groups and poor clusters implies that large numbers of progenitors exist in low-sigma systems at modest redshifts (~ 0.5), where morphologies and internal kinematics are within the measurement range of current technology.