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Radio Lobes (radio + lobe)
Selected AbstractsSpatially Resolved Very Large Array 74 MHz Observations Toward the Galactic CenterASTRONOMISCHE NACHRICHTEN, Issue S1 2003C. L. Brogan Abstract We present the highest resolution and sensitivity low frequency image (<300 MHz) of the Galactic center to date using the Very Large Array at 74 MHz in its A, B, C, & D configurations. The resulting images have a resolution of 2.1, × 1.2, and a dynamic range of ,400 From this data we have been able to identify a region of enhanced 74 MHz emission about 5° in extent that is coincident with the high density molecular gas surrounding the Galactic center known as the Central Molecular Zone. In addition to giving an unprecedented view of the extended nonthermal emission surrounding the Galactic center, the 74 MHz image shows deep free-free absorption across the Galactic center itself, as well as, part of the Galactic center radio lobe, and a number of H II regions in the field. This absorption is due to ionized thermal gas in front of, or in some cases embedded in, the nonthermal Galactic center (GC) emission. Such absorption allows us to unambiguously place some of the H II regions in the direction of the GC along the line of sight for the first time. The morphology, nature, and relationship to the Galactic center of the 74 MHz absorption and emission is discussed. [source] X-ray groups and clusters of galaxies in the Subaru,XMM Deep FieldMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2010A. Finoguenov Abstract We present the results of a search for galaxy clusters in the Subaru,XMM Deep Field (SXDF). We reach a depth for a total cluster flux in the 0.5,2 keV band of 2 × 10,15 erg cm,2 s,1 over one of the widest XMM,Newton contiguous raster surveys, covering an area of 1.3 deg2. Cluster candidates are identified through a wavelet detection of extended X-ray emission. The red-sequence technique allows us to identify 57 cluster candidates. We report on the progress with the cluster spectroscopic follow-up and derive their properties based on the X-ray luminosity and cluster scaling relations. In addition, three sources are identified as X-ray counterparts of radio lobes, and in three further sources, an X-ray counterpart of the radio lobes provides a significant fraction of the total flux of the source. In the area covered by near-infrared data, our identification success rate achieves 86 per cent. We detect a number of radio galaxies within our groups, and for a luminosity-limited sample of radio galaxies we compute halo occupation statistics using a marked cluster mass function. We compare the cluster detection statistics in the SXDF with that in the literature and provide the modelling using the concordance cosmology combined with current knowledge of the X-ray cluster properties. The joint cluster log(N) , log(S) is overpredicted by the model, and an agreement can be achieved through a reduction of the concordance ,8 value by 5 per cent. Having considered the dn/dz and the X-ray luminosity function of clusters, we conclude that to pin down the origin of disagreement a much wider (50 deg2) survey is needed. [source] The ionization of the emission-line gas in young radio galaxiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2009J. 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] Impact of tangled magnetic fields on fossil radio bubblesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2007M. Ruszkowski ABSTRACT There is growing consensus that feedback from active galactic nuclei (AGN) is the main mechanism responsible for stopping cooling flows in clusters of galaxies. AGN are known to inflate buoyant bubbles that supply mechanical power to the intracluster gas [intracluster medium (ICM)]. High Reynolds number hydrodynamical simulations show that such bubbles get entirely disrupted within 100 Myr, as they rise in cluster atmospheres, which is contrary to observations. This artificial mixing has consequences for models trying to quantify the amount of heating and star formation in cool core clusters of galaxies. It has been suggested that magnetic fields can stabilize bubbles against disruption. We perform magnetohydrodynamical simulations of fossil bubbles in the presence of tangled magnetic fields using the high-order pencil code. We focus on the physically motivated case where thermal pressure dominates over magnetic pressure and consider randomly oriented fields with and without maximum helicity and a case where large-scale external fields drape the bubble. We find that helicity has some stabilizing effect. However, unless the coherence length of magnetic fields exceeds the bubble size, the bubbles are quickly shredded. As observations of Hydra A suggest that length-scale of magnetic fields may be smaller than typical bubble size, this may suggest that other mechanisms, such as viscosity, may be responsible for stabilizing the bubbles. However, since Faraday rotation observations of radio lobes do not constrain large-scale ICM fields well if they are aligned with the bubble surface, the draping case may be a viable alternative solution to the problem. A generic feature found in our simulations is the formation of magnetic wakes where fields are ordered and amplified. We suggest that this effect could prevent evaporation by thermal conduction of cold H, filaments observed in the Perseus cluster. [source] A multi-wavelength view of the archetypical CSS radio galaxy 3C303.1: Evidence for shocks and induced star formationASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009C.P. O'Dea Abstract I discuss multi-wavelength data on the archetypal CSS radio galaxy 3C303.1. The radio source is sub-galactic in scale where it can directly affect the ISM of the host galaxy. The emission line kinematics and ionization diagnostics are consistent with energy input from shocks driven by the radio source. The Spitzer IRS spectrum indicates that star formation is occurring in the host galaxy. The HST/ACS/HRC UV image shows UV light which is aligned with the radio source axis. I suggest that the UV light is from young stars which have been triggered by the radio lobes. XMM observations detect the ISM of the host galaxy with a temperature of 0.8 keV plus an additional component whose properties are not well defined. I suggest the second component is a hot shocked gas (T = 45 keV) consistent with a Mach number of 13 for the expanding bow shock. Thus, the multi-wavelength data give a consistent picture in which the radio source drives shocks into the ISM which ionize dense clouds, trigger star formation, and shock heat the hot component of the ISM to very high temperature. These observations demonstrate that radio sources can provide significant feedback to their host galaxy (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||