Evolution of AGN Space Densities and the FR Dichotomy

We focus on a comparison of the space densities of FRI and FRII extended radio sources at different epochs, and find that FRI and FRII sources show similar space density enhancements in various redshift ranges, possibly implying a common evolution.Comment: IAU Symposium 267 Proceeding - 1 pag

Resolving the masers in M82

Despite first being detected in the 1970s, surprisingly little is known about the OH main line maser population in the nearby starburst galaxy M82. Sometimes referred to as 'kilomasers', they have isotropic luminosities intermediate between Galactic masers and those found in more distant megamasers. Several observations have been carried by this group over the last ten years in an attempt to get a better handle on their nature. High velocity resolution VLA observations in 2006 showed that almost all of the maser spots, distributed across the central arcminute of the galaxy, were apparently coincident with background continuum features, and a handful displayed multiple velocity components. The majority of those with velocity structure are located on a blue-shifted arc in the pv-plane, spatially located on an arc northward of the peculiar source known as B41.95+57.5. Now, new results from high spatial and spectral resolution observations with the EVN have resolved several of these masers into multiple spatial components for the first time. The maser emission is compared with known continuum sources in the galaxy, and we conclude that at least some of the maser emission is from high-gain maser action.Comment: Six pages, one table, one figure. To appear in proceedings of the 11th EVN Symposium (Bordeaux, 9-12 October 2012

Space densities and unified models of AGN

Using combined information from both FIRST and NVSS radio surveys at 1.4GHz, a sample of 282 sources with Slim = 1.3Jy was constructed. Radio morphological type were determined for each sources, and redshift information was found for 94% of the sample members, from databases such as SIMBAD and SDSS. A source count at 1.4 GHz was constructed from results in the literature. Space-density models using the Wall, Pearson & Longair (1980) technique were then applied using the sample and the source count; parameters for these models were optimized for the entire sample, as well as for the sample of extended sources only. In both cases, it was found that an exponential evolution with Pt = alog(z) + b gave the best fit. In the case of the entire sample, the V/Vmax statistics was computed, where = 0.6113 with σ = 0.0174. This project was mainly a pilot study to determine if the modeling of the luminosity function and epoch dependence of radio AGN was possible, primarily using the FIRST and NVSS samples in a complementary manner. This is a further way in which these huge radio surveys may be exploited for cosmological purposes and physical understanding of AGN. Since this study was successful, future work will involve using samples from FIRST and NVSS at different flux limits and applying this and much more sophisticated modeling techniques to determine the evolutions of the FRI and FRII populations separately. Ultimately, the goal of such a project would be to compare these evolutions and to use them as bases to derive new versions of the dual-population unified model described by Wall & Jackson (1997). This unified model has been successful until now but these new data should provide a comprehensive test--which may reject the formulation; or may suggest modifications that further our physical insight into the hosting/beaming paradigm of powerful radio AGN.Science, Faculty ofPhysics and Astronomy, Department ofGraduat

Space densities of AGN and the FR dichotomy

Extended double-lobe radio sources can be morphologically classified into two groups: Fanaroff-Riley (FR) type I sources have the highest surface brightness along the jets near the core and FR type II sources show the highest surface brightness at the lobe extremities, as well as more collimated jets. This thesis work focuses on a comparison of the space densities of FRI and FRII sources at different epochs, with a particular focus on FRI sources. First, we present the construction of the Combined NVSS-FIRST Galaxy catalogue (CoNFIG), a new sample of radio sources at 1.4 GHz. It includes VLA observations, FRI/FRII morphology classifications, optical identifications and redshift estimates. The final catalogue consists of 858 sources over 4 samples (CoNFIG-1, 2, 3 and 4 with flux density limits of S₁.₄_GHz=1.3, 0.8, 0.2 and 0.05 Jy respectively). It is 95.7% complete in radio morphology classification and 74.3% of the sources have redshift data. Combining CoNFIG with complementary samples, the distribution and cosmic evolution of FRI and FRII sources are investigated. We find that FRI sources undergo mild evolution and that, at the same radio luminosity, FRI and FRII sources show similar space density enhancements in various redshift ranges, implying a common mechanism powering the luminosity-dependent evolution. This improved understanding of radio galaxy evolution will also give better insight into the the physics of AGN and their role in galaxy formation.Science, Faculty ofPhysics and Astronomy, Department ofGraduat