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Compact Radio Sources (compact + radio_source)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

The ionization of the emission-line gas in young radio galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2009
J. Holt
ABSTRACT This paper is the second in a series in which we present intermediate-resolution, wide-wavelength coverage spectra for a complete sample of 14 compact radio sources, taken with the aim of investigating the impact of the nuclear activity on the circumnuclear interstellar medium (ISM) in the early stages of radio source evolution. In the first paper (Holt, Tadhunter & Morganti), we presented the kinematic results from the nuclear emission-line modelling and reported fast outflows in the circumnuclear gas. In this paper, we use the line fluxes to investigate the physical conditions and dominant ionization mechanisms of the emission-line gas. We find evidence for large electron densities and high reddening in the nuclear regions, particularly in the broader, blueshifted components. These results are consistent with the idea that the young, recently triggered radio sources still reside in dense and dusty cocoons deposited by the recent activity triggering event (merger/interaction). In addition, we find that the quiescent nuclear and extended narrow components are consistent with active galactic nucleus (AGN) photoionization, split between simple-slab AGN photoionization and mixed-medium photoionization models. For the nuclear broader and shifted components, the results are less clear. Whilst there are suggestions that the broader components may be closer to shock plus precursor models on the diagnostic diagrams, and that the electron temperatures and densities are high, we are unable to unambiguously distinguish the dominant ionization mechanism using the optical emission-line ratios. This is surprising given the strong evidence for jet,cloud interactions (broad emission lines, large outflow velocities and strong radio-optical alignments), which favours the idea that the warm gas has been accelerated in shocks driven by the radio lobes expanding through a dense cocoon of gas deposited during the triggering event. [source]

Are radio-loud Broad Absorption Line Quasars young sources?

ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009
F.M. Montenegro-Montes
Abstract Studying Broad Absorption Line Quasars (BAL QSOs) is interesting because they probe the physics of the AGN environment, and because AGN outflows are important ingredients in many recent astrophysical puzzles. In the last decade, a substantial population of radio BAL QSOs was discovered and we have started a characterisation of the radio-loud BAL QSO population studying their radio spectra, radio morphology and polarisation properties. Our high-resolution radio maps show that BAL QSOs are compact radio sources with projected linear sizes below 1 kpc. Most BAL QSOs in our sample are unpolarised or weakly polarised at 8.4 GHz. They display convex radio spectra which typically flatten at low frequencies and become steeper at high frequencies, i.e. above 20 GHz. Many of these characteristics are common to the population of young radio sources, like Compact Steep Spectrum (CSS) or Gigahertz-Peaked Spectrum (GPS) sources. The above supports the hypothesis that BAL QSOs might be related to the initial stages in the AGN evolution (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Gas and stars in compact (young) radio sources

ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009
R. Morganti
Abstract Gas can be used to trace the formation and evolution of galaxies as well as the impact that the nuclear activity has on the surrounding medium. For nearby compact radio sources, we have used observations of neutral hydrogen , that we detected in emission distributed over very large scales , combined with the study of the stellar population and deep optical images to investigate the history of the formation of their host galaxy and the triggering of the activity. For more distant and more powerful compact radio sources, we have used optical spectra and H I , in absorption , to investigate the presence of fast outflows that support the idea that compact radio sources are young radio loud AGN observed during the early stages of their evolution and currently shredding their natal cocoons through extreme circumnuclear outflows. We will review the most recent results obtained from these projects (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Optical spectra of 15 Low Luminosity Compact Sources and the formation of jets

ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009
S. Buttiglione
Abstract We present the results of optical spectroscopy of 15 compact radio sources, selected to be among the lowest luminosity objects and expected to evolve into FR I radio galaxies. The aim of the work is to exploit the emission line characteristics as indicators of the nuclear activity , in terms of accretion properties , during the early stages of the production of jets. The emission line ratios identify most Low Luminosity Compact Sources (LLCSs) as low excitation galaxies, similar to evolved FR I. Also in terms of their optical , radio properties they appear to be indistinguishable from FR I. These findings support the view that jets could be produced by nuclei accreting both at high and low rates (and/or radiatively efficient and inefficient discs). They also argue against the idea that FRI represent a late stage after a powerful FR II phase (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

X-ray emission from GPS and CSS sources

ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009
A. Siemiginowska
Abstract Many X-ray observations of GigaHertz Peaked Spectrum and Compact Steep Spectrum sources have been made with Chandra X-ray Observatory and XMM-Newton Observatory over the last few years. The X-ray spectra contribute the important information to the total energy distribution of the compact radio sources. In addition the spatial resolution of Chandra allows for studies of the X-ray morphology of these sources on arcsec scales and provide a direct view of their environments. This paper gives a review of the current status of the X-ray observations and their contribution to our understanding of the nature of these compact radio sources. It also describes primary physical processes that lead to the observed X-ray emission and summarize X-ray emission properties expected from interactions between an expanding radio source and the intergalactic environment (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Interaction of radio jets with clouds in the ambient medium: Numerical simulations

ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009
S. JeyakumarArticle first published online: 13 FEB 200
Abstract Hydrodynamical simulations of jets interacting with clouds moving in the ambient medium of the host galaxy are presented. Clouds with sizes of the order of the jet diameter and smaller, crossing the path of the jet with different speeds are considered. In the case of slow moving clouds the jet is stopped over the brief period of time taken by the cloud to cross the jet. The jet maintains its general morphology in the case of fast moving clouds. Erosion of the clouds leads to redistribution of cloud material to large distances. Such interaction may explain the large outflow velocities observed from pc to kpc scales in the compact radio sources (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Preparation of multi-frequency monitoring of compact radio sources with the KVN

ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009
B.W. Sohn
Abstract The Korean VLBI network is the first VLBI network in Korea dedicated to mm-VLBI. Its multi-frequency phase referencing technique ensures high image sensitivity and high temporal resolution observations. Here we outline our research plans of compact young radio sources with this new facility (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]