Exploring the Impact of Galaxy Interactions over Seven Billion Years with CAS

TL;DR

This study uses the CAS system to analyze galaxy interactions over seven billion years, comparing morphological parameters and star formation rates in normal versus disturbed galaxies from HST data.

Contribution

It evaluates the effectiveness of CAS criteria in distinguishing galaxy types across redshifts and compares star formation activity between normal and interacting galaxies.

Findings

CAS criteria effectively separate disturbed from normal galaxies at various redshifts.

Interacting galaxies show higher star formation rates than normal galaxies.

The cosmic star formation rate density differs between galaxy types over time.

Abstract

We explore galaxy assembly over the last seven billion years by characterizing "normal" galaxies along the Hubble sequence, against strongly disturbed merging/interacting galaxies with the widely used CAS system of concentration (C), asymmetry (A), and 'clumpiness' (S) parameters, as well as visual classification. We analyze Hubble Space Telescope (HST) ACS images of ~4000 intermediate and high mass (> 10^9 solar masses) galaxies from the GEMS survey, one of the largest HST surveys conducted to date in two filters. We explore the effectiveness of the CAS criteria [A>S and A>~0.35] in separating normal and strongly disturbed galaxies at different redshifts, and quantify the recovery and contamination rate. We also compare the average star formation rate and the cosmic star formation rate density as a function of redshift between normal and interacting systems identified by CAS.