The environments of radio sources in the GLASS survey

The GAMA Legacy ATCA Southern Survey (GLASS) observed a 50 square degree region of the southern sky to 20 ˜í¬¿Jy beam\\(^{-1}\\) RMS at 5.5 GHz and 35 ˜í¬¿Jy beam\\(^{-1}\\) RMS at 9.5 GHz using the Australia Telescope Compact Array (ATCA). This survey targets the GAMA G23 field, one of the foremost legacy regions in the southern sky, with extensive multi-wavelength coverage. This thesis combines radiofrequency observations with optical and mid-infrared catalogues to quantify the environments of various radio source populations. I visually identify associated radio components (e.g. cores, lobes and hotspots) to produce integrated radio source catalogues. A cross-matched 5.5 GHz and 9.5 GHz catalogue for the initial 8 square degree region of the G23 field includes 2609 radio sources. The 150 visually extended radio galaxies are further classified based on the morphology of their synchrotron-emitting radio lobes. I construct a GLASS-selected multi-wavelength catalogue comprising: two additional radio frequencies (400 and 888 MHz); four mid-infrared (MIR) bands (3.4 - 22 ˜í¬¿m) from the Widefield Infrared Survey Telescope (WISE); and optical spectroscopy, optical and near-infrared photometry, and galaxy group and cluster information from the Galaxy Mass and Assembly (GAMA) survey. I identify compact radio sources as active galactic nuclei (AGN) and their various sub-populations, using optical spectroscopy, WISE MIR colours, and the MIR-radio correlation. The environments of a range of AGN sub-populations in a complete volume-limited sample (z ‚Äöv¢¬ß 0:25) are compared to a corresponding control sample of GAMA galaxies. I investigate the variation in galaxy stellar mass, group richness, and location within the group as a function of radio AGN, optical AGN and radio AGN sub-types. I find that radio AGN are hosted by more massive galaxies than optical AGN and galaxies in the control sample of star-forming galaxies by approximately 0.45 dex, and 0.8 dex, respectively. I also find that the fraction of galaxies hosting radio-loud AGN and optical AGN is a strong function of the host galaxy stellar mass, consistent with the findings of other authors in the literature. Furthermore, I find that the mass of low excitation radio galaxies (LERGs) are 0.42 dex more massive than high excitation radio galaxies (HERGs); intriguingly, I find no preference for extended radio AGN to be hosted by either HERGs or LERGs. The group environments of the radio AGN populations are compared against mass-matched control samples. Radio AGN hosted by low mass galaxies (10\\(^{10.5}\\) ‚Äöv¢¬ß M\\(_*\\)/M\\(_'\\) < 10\\(^{11.25}\\)) are preferentially located in poor groups, with no dependence on their location within the group. However, radio AGN, in general, show no preference to be hosted in either rich or poor groups group environments, although those in groups are typically found at the centre. I find that optical AGN are preferentially located in poor groups over rich groups, although at no significant abundance at either the centre or edges. Finally, I found compact radio sources in poor and rich groups have very different spectral indices suggesting the compact population comprises a variety of objects with differing emission mechanisms. This work presents one of the largest samples of radio AGN with broadband SEDs and host galaxy/group environment information. When combined with radio source dynamical models, the catalogue constructed in this work will provide a unique opportunity to test jet triggering and feedback mechanisms and their relation to the environment.