Cosmological effects on Size Evolution of some Extragalactic Radio Sources and Quasar/Galaxy Unification

We use analytical methods to develop a mathematical model that expresses the relationship between the linear size of some extragalactic radio sources (EGRS) and their redshift . Result shows that , where . For the purpose of obtaining an empirical relation of similar form, we carry out simple linear regression analyses of the observed linear sizes of these EGRS in our sample against their respective observed redshifts. We obtain an empirical relation of the form, , where and for radio-loud quasars and radio galaxies respectively, with correlation coefficients given by, for each of the sources. The correlation is marginal/slight. Comparing the theoretical and empirical relations, we find that the data show an inverse correlation which is similar to the theory. This suggestively indicates presence of cosmological effects on the size evolution of the radio sources. Moreover, we find that similarity in the behavior of the two sources in the plane, simply supports quasar/galaxy unification scheme in which the different observable properties that characterize these two subclasses of radio sources are aspect-dependent.

Variable jet Lorentz factors can explain soft self-absorbed radio spectra of accreting black holes

We study the effect of variable jet bulk Lorentz factors, i.e. either jet acceleration or deceleration, on partially synchrotron self-absorbed radio spectra from cores of radio-loud active galactic nuclei and black hole binaries in the hard state. In about a half of quasars and radio galaxies, their core radio spectra are observed to be soft, i.e. have the spectral index of α < 0. If they are emitted by jets with constant Lorentz factors, that softness implies deposition of large amounts of energy at large distances from the centre. We show here that such soft spectra can be explained without that energetic requirement by emission of jets with the Doppler factor increasing with the distance. This can happen for either jet acceleration or deceleration, depending on the jet viewing angle. We find our model can explain the quiescent radio to X-ray spectra of the BL Lac objects Mrk 421 and Mrk 501.

Extragalactic jets as probes of distant clusters of galaxies and the clusters occupied by bent radio AGN (COBRA) survey

We are conducting a large survey of distant clusters of galaxies using radio sources with bent jets and lobes as tracers. These radio sources are driven by AGN and achieve their bent morphologies through interaction with the surrounding gas found in clusters of galaxies. Based on low-redshift studies, these types of sources can be used to identify clusters very efficiently. We present initial results from our survey of 653 bent-double radio sources with optical hosts too faint to appear in the SDSS. The sample was observed in the infrared with Spitzer, and it has revealed ~200 distant clusters or proto-clusters in the redshift range z ~ 0.7 - 3.0. The sample of bent-doubles contains both quasars and radio galaxies enabling us to study both radiative and kinetic mode feedback in cluster and group environments at a wide range of redshifts.

An Updated Multi-Wavelength Radio and Optical Catalog of Quasars and Radio Galaxies

We present a catalog of millions of radio sources, created by consolidating large-area radio and optical surveys GB6 (6cm), FIRST (20cm), NVSS (20cm), WENSS (92cm), VLSS (4m), and SDSS DR9 (optical). The region where all surveys overlap covers 3269 deg2 in the North Galactic Cap, and contains >160,000 20-cm sources, with about 12,000 detected in all five radio surveys and over one-third detected optically. Combining parameters from the sky surveys allows easy and efficient classification by radio and optical morphology and radio spectral index. The catalog is available at http://www.atnf.csiro.au/people/Amy.Kimball/radiocat.shtml.

The AGN content of deep radio surveys and radio emission in radio-quiet AGN. Why every astronomer should care about deep radio fields

We present our very recent results on the sub-mJy radio source populations at 1.4 GHz based on the Extended Chandra Deep Field South VLA survey, which reaches ~ 30 μJy, with details on their number counts, evolution, and luminosity functions. The sub-mJy radio sky turns out to be a complex mix of star-forming galaxies and radio-quiet AGN evolving at a similar, strong rate and declining radio-loud AGN. While the well-known flattening of the radio number counts below 1 mJy is mostly due to star-forming galaxies, these sources and AGN make up an approximately equal fraction of the sub-mJy sky. Our results shed also light on a fifty-year-old issue, namely radio emission from radio-quiet AGN, and suggest that it is closely related to star formation, at least at z ~ 1.5 − 2. The implications of our findings for future, deeper radio surveys, including those with the Square Kilometre Array, are also discussed. One of the main messages, especially to non-radio astronomers, is that radio surveys are reaching such faint limits that, while previously they were mainly useful for radio quasars and radio galaxies, they are now detecting mostly star-forming galaxies and radio-quiet AGN, i.e., the bulk of the extragalactic sources studied in the infrared, optical, and X-ray bands.

The Jets in Micro-Quasars and Quasars: A Comparison

The discovery of relativistic jets in radio emitting X-ray binaries in our own galaxy has led to the term ‘microquasar’ being coined for these objects. In this paper the properties of microquasars are compared with those of quasars and radio galaxies, with the aim of trying to see how the similarities and differences can inform us about the physical conditions and evolution of jets. GRS1915+105 and SS433 are also discussed in more detail.