Active Galaxies NewsletterAn electronic publication dedicated to the observations and theory of active galaxies
Edited by Melanie Gendre
Below is a list of abstracts posted in the Newsletter in the past 6 months, along with relevant contact links.
Please note that the latest abstract can be found in the recent issues of the newsletter.
Radio-loud active galactic nuclei where one of the jets is directed towards the observer at a small angle to the line of sight are known as blazars. Now is a particularly exciting time in blazar research, as the recently launched Fermi gamma-ray space telescope has detected hundreds of blazars at gamma-ray energies, allowing true multiwavelength studies of large samples of these objects for the first time. However, blazar research is plagued by selection effects, which has hindered progress in their understanding.
The majority of this Thesis involves the definition and exploitation of a new sample of nearby flat spectrum core-dominated radio sources, the Survey of Extragalactic Nuclear Spectral Energies (SENSE) sample, which contains 121 blazar-like objects. While the sample was designed to contain sources with similar core radio properties, no restrictions were placed on the optical properties, so the sample contains the expected BL Lacs, as well as passive elliptical galaxies, and some optical AGN. 25 SENSE sources are currently without redshifts. Work carried out using SDSS images to separate the host galaxy from the AGN core indicates that higher resolution images would allow the host galaxies to be detected and characterised so that the redshift could be estimated.
It was found that the SENSE sample shows no evidence for cosmological evolution using the <V/Vmax> test. This result is consistent with the SENSE sample being the beamed versions of FR-I galaxies. 78% of the SENSE sample show extended emission in available radio maps, and the extended luminosities of these sources are also consistent with a FR-I parent population. Cross-correlation of the SENSE sample with the second catalogue from the Fermi gamma-ray space telescope (2FGL) revealed that only 29 of the SENSE sources are gamma-ray loud. The properties of these gamma-ray detected sources were compared to the rest of the sample and no difference could be found in the available data.
The small number of SENSE sources detected by Fermi meant that the sample could not be used to investigate the relationship between synchrotron and inverse Compton emission in blazars. Instead, the CRATES radio catalogue was cross-correlated with 2FGL. The Compton efficiency parameter was defined as the ratio of (νSν) at the inverse Compton SED peak to (νSν) at radio frequencies. No difference was found between the Compton efficiencies of BL Lacs and FSRQs, indicating that the high energy emission in blazars is dominated by the synchrotron self-Compton process.
Dennis Sciama Building, Burnaby Road, PO1 3FX Portsmouth, U.K.
Radio galaxies and quasars are among the largest and most powerful single objects known and are believed to have had a significant impact on the evolving Universe and its large scale structure. Their jets inject a significant amount of energy into the surrounding medium, hence they can provide useful information in the study of the density and evolution of the intergalactic and intracluster medium. The jet activity is also believed to regulate the growth of massive galaxies via the AGN feedback.
In this thesis I explore the intrinsic and extrinsic physical properties of the population of Fanaroff-Riley II (FR II) objects, i.e. their kinetic luminosities, lifetimes, and central densities of their environments. In particular, the radio and kinetic luminosity functions of these powerful radio sources are investigated using the complete, flux limited radio catalogues of 3CRR and BRL. I construct multidimensional Monte Carlo simulations using semi-analytical models of FR II source time evolution to create artificial samples of radio galaxies. Unlike previous studies, I compare radio luminosity functions found with both the observed and simulated data to explore the best-fitting fundamental source parameters. The Monte Carlo method presented here allows one to: (i) set better limits on the predicted fundamental parameters of which confidence intervals estimated over broad ranges are presented, and (ii) generate the most plausible underlying parent populations of these radio sources. Moreover, I allow the source physical properties to co-evolve with redshift, and I find that all the investigated parameters most likely undergo cosmological evolution; however these parameters are strongly degenerate, and independent constraints are necessary to draw more precise conclusions. Furthermore, since it has been suggested that low luminosity FR IIs may be distinct from their powerful equivalents, I attempt to investigate fundamental properties of a sample of low redshift, low radio luminosity density radio galaxies. Based on SDSS-FIRST-NVSS radio sample I construct a low frequency (325 MHz) sample of radio galaxies and attempt to explore the fundamental properties of these low luminosity radio sources. The results are discussed through comparison with the results from the powerful radio sources of the 3CRR and BRL samples.
Finally, I investigate the total power injected by populations of these powerful radio sources at various cosmological epochs and discuss the significance of the impact of these sources on the evolving Universe. Remarkably, sets of two degenerate fundamental parameters, the kinetic luminosity and maximum lifetimes of radio sources, despite the degeneracy provide particularly robust estimates of the total power produced by FR IIs during their lifetimes. This can be also used for robust estimations of the quenching of the cooling flows in cluster of galaxies.