Merging Galaxies with Tidal Tails in COSMOS to z=1

TL;DR

This study identifies and analyzes long tidal tails in merging galaxies up to redshift 1, revealing their evolution, frequency, and significance in galaxy assembly history using HST imaging and a novel detection method.

Contribution

It introduces a new $A_{ m O}-D_{ m O}$ technique for detecting tidal tails and provides the first statistical analysis of their occurrence and evolution up to z=1.

Findings

Tidal tail merger fraction evolves as (1+z)^{2.0±0.4}

Higher prevalence of tidal tails in less massive galaxies at z=1

Occurrence rate of tidal-tail mergers is approximately 0.01 Gyr^{-1} at z=1

Abstract

Tidal tails are created in major mergers involving disk galaxies. How the tidal tails trace the assembly history of massive galaxies remains to be explored. We identify a sample of 461 merging galaxies with long tidal tails from 35076 galaxies mass-complete at $M_\star\ge 10^{9.5}\,M_{\odot}$ and $0.2\leq z\leq1$ based on HST/ACS F814W imaging data and public catalogs of the COSMOS field. The long tails refer to these with length equal to or longer than the diameter of their host galaxies. The mergers with tidal tails are selected using our novel $A_{\rm O}-D_{\rm O}$ technique for strong asymmetric features together with visual examination. Our results show that the fraction of tidal-tailed mergers evolves mildly with redshift, as $\sim (1+z)^{2.0\pm0.4}$, and becomes relatively higher in less massive galaxies out to $z=1$. With a timescale of 0.5 Gyr for the tidal-tailed mergers, we obtain that the occurrence rate of such mergers follows $0.01\pm 0.007\,(1+z)^{2.3\pm 1.4}$ Gyr$^{-1}$ and corresponds to $\sim0.3$ events since $z=1$ and roughly one-third of the total budget of major mergers from the literature. For disk-involved major mergers, nearly half of them have undergone a phase with long tidal tails