A Multi-wavelength Investigation of the Gas-rich Dwarf Galaxy Populations of Three Interacting Groups: NGC 3166/9, NGC 871/6/7 and NGC 4725/47

Abstract

This thesis presents one of the first unbiased investigations of the first- and second-generation gas-rich dwarf galaxy populations of nearby interacting groups. Individually, these low-mass objects offer information about the evolutionary history of their respective groups. Collectively, the multi-wavelength dataset presented here enables direct comparison of the properties and prevalence of gas-rich dwarfs to those predicted by numerical simulations, particularly the tidal objects. Starting with HI maps from the blind Arecibo Legacy Fast ALFA survey (ALFALFA), three nearby groups: NGC 3166/9, NGC 871/6/7 and NGC 4725/47 were selected for high-resolution HI follow-up and deep optical imaging. Observations from the Giant Metrewave Radio Telescope (GMRT) are able to identify and resolve the HI belonging to the low-mass group members, thereby enabling gas and dynamical mass measurements. Deep g'r'i'-band optical photometry, from the Canada-France-Hawaii Telescope (CFHT) MegaCam, is used to infer the stellar masses, ages and metallicities of putative optical counterparts to these gas-rich detections. The combination of HI and optical data allows for dynamical to baryonic mass calculations and stellar population estimates that facilitate the distinction between and classification of dwarf irregulars (dIrrs), short-lived tidal knots and tidal dwarf galaxies (TDGs). Overall, the three groups in this study contain a total of eight spiral galaxies, at least eight dIrrs, four tidal knots (with M_HI ~ 10^7 M_sol) that are likely short-lived, and four tidal knots containing sufficient gas to survive and evolve into long-lived TDGs. This result implies that there are ~1.3 long-lived galaxy-like tidal features per interacting spiral galaxy pair, which is consistent with standard cosmological galaxy interaction simulations. The tidal objects examined in this survey also appear to have a wider variety of properties than the TDGs formed in current simulations, which could be the result of pre- or post-formation environmental influences.