Tidal Dwarf Galaxies at Intermediate Redshifts

TL;DR

This study measures the formation rate of tidal dwarf galaxies at intermediate redshifts using deep HST imaging, finding they contribute minimally to the local dwarf galaxy population and are characterized by young stellar populations.

Contribution

First estimation of tidal dwarf galaxy production rate at 0.5<z<1.1 using morphological analysis of deep imaging data.

Findings

Estimated TDG production rate is about 1.4×10^{-5} per Gyr per volume.

Less than 10% of local dwarf galaxies are likely tidally-originated.

TDGs show signs of recent star formation with ages around 200-400 Myr.

Abstract

We present the first attempt at measuring the production rate of tidal dwarf galaxies (TDGs) and estimating their contribution to the overall dwarf population. Using HST/ACS deep imaging data from GOODS and GEMS surveys in conjunction with photometric redshifts from COMBO-17 survey, we performed a morphological analysis for a sample of merging/interacting galaxies in the Extended Chandra Deep Field South and identified tidal dwarf candidates in the rest-frame optical bands. We estimated a production rate about 1.4 {\times} 10^{-5} per Gyr per comoving volume for long-lived TDGs with stellar mass 3 {\times} 10^{8-9} solar mass at 0.5<z<1.1. Together with galaxy merger rates and TDG survival rate from the literature, our results suggest that only a marginal fraction (less than 10%) of dwarf galaxies in the local universe could be tidally-originated. TDGs in our sample are on average bluer than their host galaxies in the optical. Stellar population modelling of optical to near-infrared spectral energy distributions (SEDs) for two TDGs favors a burst component with age 400/200 Myr and stellar mass 40%/26% of the total, indicating that a young stellar population newly formed in TDGs. This is consistent with the episodic star formation histories found for nearby TDGs.