Tracing environmental processes using cold dust with the Herschel Space Observatory

• Main Author: Fuller, Christopher
• Published: Cardiff University 2014
• Subjects: 523.8; QB Astronomy
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637132

This thesis presents an investigation into the effect of environment on a galaxy's ISM. I have used new data from the Herschel Space Observatory, which detects the peak of far-infrared (FIR) emission from cold dust (20 K) in nearby galaxies. Using data from the Herschel Fornax Cluster Survey (HeFoCS) and the Herschel Astrophysical Large Area Terahertz Survey (H-ATLAS) I have measured the FIR fluxes of galaxies in the nearby Fornax cluster and Coma region. In order to measure these FIR fluxes I used the optical shape and size of galaxies as a starting point. In the case of Fornax there was already a high quality optical catalogue, the Fornax Cluster Catalogue (FCC; Ferguson, 1989). However, in the case of the Coma cluster and filament I created my own using data from the SDSS spectroscopic survey, selecting galaxies based on position and velocity. Thus, creating the Coma Cluster Catalogue (CCC) and Coma Filament Catalogue (CFC). For galaxies detected in at least 3 and 5 Herschel bands for the HeFoCS and H-ATLAS galaxies, respectively, I fitted a modified blackbody with a fixed beta emissivity index of 2, yielding dust masses and temperatures for 22 and 198 HeFoCS and H-ATLAS galaxies, respectively. All Early-type galaxies showed a lower mean dust mass and hotter temperature than found for late-types. When comparing early-type galaxies across all sampled environments, their FIR properties are found to be statistically identical. I only find a significant difference in dust-to-stellar mass for late-type galaxies between the filament and a field sample. This may suggest that the effect of the cluster and filament is more subtle than previously thought and that the evolution of the ISM components has mostly taken place well before the cluster was assembled. I use a method to compare multiple parameters for the Coma cluster and filament galaxies and how each is a�ected by local environmental density. Late types show a moderate change in most parameters with the exception of gas-to-stars, which is strongly affected by environmental density. I suggest that late-types' lower sSFRs and higher stellar masses in the cluster when compared to the filament indicate that the galaxies in the cluster formed earlier and are hence more evolved. In order to understand how the baryonic components of the galaxies change as a whole between the cluster and filament I have created mass functions. Using Schechter function fits to stellar, gas and dust mass density ratios for the Coma cluster and filament I calculated the ratio of gas-to-stellar and dust-to-stellar mass densities for each environment finding that Virgo, Fornax, Coma and the filament were gas deficient when compared to the field, but all their dust mass functions appeared identical. This further demonstrates that dust is largely invariant to environment, whereas, gas is affected well before entry into the cluster.