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GPS Sources (gps + source)
Selected AbstractsStudies of CSS/GPS sources with the Deep Space Network antennas in MadridASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009C. Garcia-Miro Abstract This contribution summarizes the antennas and receivers available at the Madrid Deep Space Communication Complex (MDSCC) and outlines the type of observations that can be performed to contribute to the study of the CSS/GPS sources. The last section provides guidelines on how to observe with the DSN antennas, and in particular at MDSCC (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Multifrequency VLBI observations of faint gigahertz peaked spectrum sourcesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2000I. A. G. Snellen We present the data and analysis of VLBI observations at 1.6, 5 and 15 GHz of a sample of faint gigahertz peaked spectrum (GPS) sources selected from the Westerbork Northern Sky Survey. The 5-GHz observations involved a global array of 16 stations and yielded data on the total sample of 47 sources. A subsample of 26 GPS sources with peak frequencies and/or peak flux densities was observed with the VLBA at 15 GHz. A second subsample of 29 sources, with was observed at 1.6 GHz using a 14-station global VLBI array. In this way, 44 of the 47 sources (94 per cent) in the sample were observed above and at or below their spectral peak. Spectral decomposition allowed us to identify three, 11, seven and two objects as compact symmetric objects, compact doubles, core,jet and complex sources, respectively. However, many of the sources classified as compact double or core,jet sources show only two components making their classification rather tentative. This may explain why the strong morphological dichotomy of GPS quasars and galaxies found for radio-bright GPS sources is not as clear in this faint sample. [source] On the evolution of young radio-loud AGNMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2000I. A. G. Snellen This paper describes an investigation of the early evolution of extragalactic radio sources using samples of faint and bright gigahertz peaked spectrum (GPS) and compact steep spectrum (CSS) radio galaxies. Correlations found between their peak frequency, peak flux density and angular size provide strong evidence that synchrotron self-absorption is the cause of the spectral turnovers, and indicate that young radio sources evolve in a self-similar way. In addition, the data seem to suggest that the sources are in equipartition while they evolve. If GPS sources evolve to large size radio sources, their redshift dependent birth-functions should be the same. Therefore, since the lifetimes of radio sources are thought to be short compared to the Hubble time, the observed difference in redshift distribution between GPS and large size sources must be due to a difference in slope of their luminosity functions. We argue that this slope is strongly affected by the luminosity evolution of the individual sources. A scenario for the luminosity evolution is proposed in which GPS sources increase in luminosity and large-scale radio sources decrease in luminosity with time. This evolution scenario is expected for a ram-pressure confined radio source in a surrounding medium with a King profile density. In the inner parts of the King profile, the density of the medium is constant and the radio source builds up its luminosity, but after it grows large enough the density of the surrounding medium declines and the luminosity of the radio source decreases. A comparison of the local luminosity function (LLF) of GPS galaxies with that of extended sources is a good test for this evolution scenario. Unfortunately, only a handful of GPS sources are known at low redshift, and an LLF can only be derived, assuming that their cosmological number density evolution is similar to that of steep spectrum sources. The LLF derived in this way is shown to be in good agreement with the proposed evolution scenario. However, the uncertainties are large, and larger, homogeneously selected samples of GPS sources are needed. [source] Long-term radio behaviour of GPS sources and candidatesASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009M. Tornikoski Abstract This paper is a summary of the work that our group has done (and recently published in several papers) on long-term radio variability of GPS sources. We have studied the long-term (up to 30 years) variability of GPS sources and candidates, with emphasis on the high-frequency radio domain. Our data sets show that only a relatively small number of these sources retain their convex spectra when they are monitored densely and for long periods of time. The current GPS samples are especially contaminated by small, beamed blazar-type sources. Also the remaining population with consistently convex GPS-type spectra seems to be heterogeneous, falling into several subpopulations when their observed properties are used for clustering them through a self-organizing map (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structure, spectra and variability of some GPS radio sourcesASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009X. Liu Abstract We report the results of multifrequency-VLBI observations of GHz-Peaked-Spectrum (GPS) radio sources. The VLBI structure and component spectra of some GPS sources are presented. Our VLBI results show that about 80% of the GPS galaxies exhibit a compact double or CSO-like structure, while the GPS quasars tend to show a core-jet. The component spectra of the GPS galaxies are often steep/convex, and the core has a flat spectrum but it is usually hidden or weak. In addition, we studied the variability of GPS sources by comparing new flux density measures, acquired with the Urumqi 25-m telescope at 4.85 GHz, with previous 87GB data. The results show that 44% of the GPS quasars varied higher than 10% in passed 20 years, while the fraction is only 12% for the GPS galaxies meaning that the GPS quasars are much more variable than GPS galaxies. In total, 25% of GPS sources show >10% variability at 4.85 GHz in our sample (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] High frequency GPS sources in the AT20G surveyASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009P.J. Hancock Abstract The Australia Telescope 20 GHz (AT20G) survey was used to select a complete sample of 656 Gigahertz Peaked Spectrum (GPS) sources with spectral turnovers above 5 GHz. The AT20G has near simultaneous observations at 4.8, 8.6 and 20 GHz, which makes it possible to exclude flat spectrum variability as a cause of a source's peaked spectrum. Optical identification of the sample results in 361 QSOs and 104 galaxies and 191 blank fields. Redshifts are known for 104 of the GPS sources. The GPS sources from the AT20G are discussed and compared to previously known samples. The new sample of high frequency peaking GPS sources is found at a lower redshift than previous samples and to also have a lower 5 GHz radio power. Evidence is found to support the idea that the origin of the GPS spectral shape are intrinsically different for galaxies and QSOs. This paper is an elaboration and extension of the talk given at the 4th CSS/GPS conference in Riccione in May this year (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Radio source populations: Results from SDSSASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009P.N. Best Abstract This contribution provides a review of our current understanding of radio source populations and their host galaxies, as derived from studies of the local Universe, in particular using the Sloan Digital Sky Survey. Evidence is presented that low luminosity radio sources are fundamentally distinct objects to high radio luminosity sources and optically or X-ray selected AGN, suggesting that these are fuelled by a different mechanism. The low-luminosity radio sources are argued to be fuelled by the accretion of hot gas from their surrounding X-ray haloes, and this offers a potential feedback loop via which the radio-loud AGN can control the cooling of the hot gas, and thus the growth of their host galaxy. The energetic output of the radio sources is derived in order to show that this is indeed feasible. It is emphasised that the difference between these two modes of AGN fuelling is distinct from that of the two different radio morphological classes of radioloud AGN (Fanaroff-Riley classes 1 and 2). The origin of the FR-dichotomy is investigated using Sloan data, and argued to be associated with the environment and evolution of the radio sources. Finally, the role of CSS and GPS sources within this picture is discussed (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Samples and statistics of CSS and GPS sourcesASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009M. Giroletti Abstract Several samples have been proposed in the last years in order to study the properties of intrinsically small sources. In this paper, we review the properties of the main samples that are currently available, both selected on the basis of spectral index and of morphology. As a result of the work in this area, large numbers of intrinsically small sources have been found. We summarize the present status of hot spot advance measurements, listing 18 sources with available VLBI data. The mean hot spot separation velocity is vsep = (0.19 ± 0.11) h,1c, and the kinematic ages span the range from 20 to 3000 years. Finally, we present a brief outlook on the use of future instrumentation in order to improve our understanding of radio source evolution. Prospects for VSOP2, e-VLA, e-MERLIN, LOFAR, ALMA, and Fermi are suggested (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] From observations to physics: Cosmological evolution of radio galaxiesASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009A.D. Kapi Abstract Recent theoretical progress has allowed us to determine the influence of the intrinsic properties of radio galaxies and their environments on their luminosity and size evolution. There are still, however, considerable uncertainties regarding our understanding of radio source evolution, in particular the relationship between CSS and GPS sources and larger radio galaxies. Here, we present our preliminary results on the cosmological evolution of the entire radio galaxy population. We use recent analytical models for the dynamical and luminosity evolution of FR II radio galaxies to convert observational data into distributions of source properties such as pressure of the source lobes. As input parameters we use the observed P - D (radio power,linear size) diagrams built up from flux-limited radio samples with complete redshift information. This allows us to examine the environments of evolving radio sources, and to shed more light on the (early) evolutionary tracks of radio galaxies (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] RubAre symmetric radio spectra of some GPS/HFP sources related to a statistical acceleration mechanism?rikASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009A. Maselli Abstract We present the results of a new spectral analysis of a sample of HFPs. We took from literature simultaneous radio measurements at various epochs and studied the symmetry of flux distribution around the peak frequency by means of a logparabolic fit. We found that a large fraction of spectra are symmetric and propose that this property may be a consequence of statistical acceleration (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||