Star formation in HI tails: HCG 92, HCG 100 and 6 interacting systems

TL;DR

This study investigates star formation in HI tails of galaxy groups, identifying young, metal-rich objects likely formed from gas ejected during galaxy interactions, with a focus on Hickson Compact Groups 92 and 100.

Contribution

It provides new spectroscopic data confirming the nature and metallicity of star-forming objects in HI tails, and compares their properties across different interacting systems.

Findings

Objects have near-solar metallicities (~8.5)

Young ages (< 100 Myr) for most objects

Higher likelihood of TDG formation in compact groups

Abstract

We present new Gemini spectra of 14 new objects found within the HI tails of Hickson Compact Groups 92 and 100. Nine of them are GALEX Far-UV (FUV) and Near-UV (NUV) sources. The spectra confirm that these objects are members of the compact groups and have metallicities close to solar, with an average value of 12+log(O/H)~8.5. They have average FUV luminosities 7 x 10^40 erg/s, very young ages (< 100 Myr) and two of them resemble tidal dwarf galaxies (TDGs) candidates. We suggest that they were created within gas clouds that were ejected during galaxy-galaxy interactions into the intergalactic medium, which would explain the high metallicities of the objects, inherited from the parent galaxies from which the gas originated. We conduct a search for similar objects in 6 interacting systems with extended HI tails, NGC 2623, NGC 3079, NGC 3359, NGC 3627, NGC 3718, NGC 4656. We found 35 UV sources with ages < 100 Myr, however most of them are on average less luminous/massive than the UV sources found around HCG 92 and 100. We speculate that this might be an environmental effect and that compact groups of galaxies are more favorable to TDG formation than other interacting systems.