共查询到20条相似文献，搜索用时 468 毫秒
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We investigate the infrared/radio correlation using the technique of source stacking, in order to probe the average properties of radio sources that are too faint to be detected individually. We compare the two methods used in the literature to stack sources and demonstrate that the creation of stacked images leads to a loss of information. We stack infrared sources in the Spitzer Extragalactic First Look Survey (xFLS) field, and the three northern Spitzer Wide-area Infrared Extragalactic survey (SWIRE) fields, using radio surveys created at 610 MHz and 1.4 GHz, and find a variation in the absolute strength of the correlation between the xFLS and SWIRE regions, but no evidence for significant evolution in the correlation over the 24-μm flux density range 150 μJy to 2 mJy. We carry out the first radio source stacking experiment using 70-μm-selected galaxies, and find no evidence for significant evolution over the 70-μm flux density range 10–100 mJy. 相似文献
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I. A. G. Snellen R. T. Schilizzi H. J. van Langevelde 《Monthly notices of the Royal Astronomical Society》2000,319(2):429-444
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. 相似文献
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We used the VLBA(NRAO, USA) and made VLBI observations towards the compact steep spectrum sources 3C43, 3C48 and 3C454 at the central frequency 1.6 GHz, and obtained their total flux density maps and information on the structures of their components. By comparison with the previous data, we analyzed the variations of their flux densities as well as the displacements of their components. It is found that the total flux density of the source 3C43, as well as the flux densities and relative positions of its components are quite stable in 14 years. For the source 3C454, the total flux density and the flux densities of its components are also relatively stable, but two of the components moved away from the central core with superluminal velocities of 21.6c and 17.7c. Fitted to their flux densities at 4 L-band frequencies, the spectral indexes of the sources 3C43 and 3C454 were obtained to be 0.63 and 0.86, respectively, in good agreement with previous results, and consistent with the definition of α ≥0.5 for compact steep spectrum sources. 相似文献
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M. J. Hardcastle L. W. Looney 《Monthly notices of the Royal Astronomical Society》2008,388(1):176-186
We have observed a small sample of powerful double radio sources (radio galaxies and quasars) at frequencies around 90 GHz with the Berkeley Illinois Maryland Association (BIMA) millimetre array, with the intention of constraining the resolved high-frequency spectra of radio galaxies. When combined with other sources we have previously observed and with data from the BIMA archive, these observations allow us for the first time to make general statements about the high-frequency behaviour of compact components of radio galaxies – cores, jets and hotspots. We find that cores in our sample remain flat-spectrum up to 90 GHz; jets in some of our targets are detected at 90 GHz for the first time in our new observations and hotspots are found to be almost universal, but show a wide range of spectral properties. Emission from the extended lobes of radio galaxies is detected in a few cases and shows rough consistency with the expectations from standard spectral ageing models, though our ability to probe this in detail is limited by the sensitivity of BIMA. We briefly discuss the prospects for radio galaxy astrophysics with Atacama Large Millimeter Array. 相似文献
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Katherine M.Blundell SteveRawlings Stephen A.Eales Gregory B.Taylor Alistair D.Bradley 《Monthly notices of the Royal Astronomical Society》1998,295(2):265-279
We describe the selection of a sample of 34 radio sources from the 6C survey from a region of sky covering 0.133 sr. The selection criteria for this sample, hereafter called 6C*, were chosen to optimize the chances of finding radio galaxies at redshift z > 4. Optical follow-up observations have already led to the discovery of the most distant known radio galaxy at z = 4.41. We present VLA radio maps and derive radio spectra for all the 6C* objects. 相似文献
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Jiang-Shui Zhang Jun-Hui FanCenter for Astrophysics Guangzhou University Guangzhou zjshui 《中国天文和天体物理学报》2003,3(5):415-422
We use observed peak and total flux densities at 6cm and 20cm to determine the spectral indices separately for the core and extended components of QSOs and galaxies, as well as their core-dominance parameters. Our results indicate that 1) Nine QSOs show both greater than 1.0 core-dominance parameters (those objects should be blazars) and greater than 0.5 spectral indices. The average core spectral index is αCore = 0.85±0.21 for the nine blazars, which implies that it is not reliable to use αradio = 0.0 for blazars. For the different subclasses, the core and extended spectral indices are as follows: for the blazars, αCore = 0.22±0.06 and αExt =0.77±0.12; the galaxies,αCore = 1.01±0.13 and αExt =0.83±0.21, and for the QSOs, αCore = 0.28±0.10 and αExt =0.68±0.08. 2) The core spectral index and core dominance parameter (R) show an anti-correlation, αC = (-1.28±0.26) log R+ (0.65 ± 0.11); 3) R is approximately linearly correlated with redshift (z). 相似文献
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J. W. Broderick J. J. Bryant R. W. Hunstead E. M. Sadler T. Murphy 《Monthly notices of the Royal Astronomical Society》2007,381(1):341-366
This paper introduces a new program to find high-redshift radio galaxies in the Southern hemisphere through ultrasteep spectrum (USS) selection. We define a sample of 234 USS radio sources with spectral indices α843 408 ≤−1.0 ( S ν ∝να ) and flux densities S 408 ≥ 200 mJy in a region of 0.35 sr, chosen by cross-correlating the revised 408 MHz Molonglo Reference Catalogue, the 843 MHz Sydney University Molonglo Sky Survey and the 1400 MHz NRAO VLA Sky Survey in the overlap region −40° < δ < −30°. We present Australia Telescope Compact Array (ATCA) high-resolution 1384 and 2368 MHz radio data for each source, which we use to analyse the morphological, spectral index and polarization properties of our sample. We find that 85 per cent of the sources have observed-frame spectral energy distributions that are straight over the frequency range 408–2368 MHz, and that, on average, sources with smaller angular sizes have slightly steeper spectral indices and lower fractional linear polarization. Fractional polarization is anticorrelated with flux density at both 1400 and 2368 MHz. We also use the ATCA data to determine observed-frame Faraday rotation measures for half of the sample. 相似文献
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Philip Lah Jayaram N. Chengalur Frank H. Briggs Matthew Colless Roberto De Propris Michael B. Pracy W. J. G. de Blok Shinobu S. Fujita Masaru Ajiki Yasuhiro Shioya Tohru Nagao Takashi Murayama Yoshiaki Taniguchi Masafumi Yagi Sadanori Okamura 《Monthly notices of the Royal Astronomical Society》2007,376(3):1357-1366
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We present a multiwavelength study of the environment of the unidentified X-ray/γ-ray sources IGR J18027–1455 and IGR J21247
+ 5058, recently discovered by the IBIS/ISGRI instrument, onboard the INTEGRAL satellite. The main properties of the sources
found inside their position error circles, give us clues about the nature of these high-energy sources. 相似文献
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J. Afonso B. Mobasher A. Hopkins A. Georgakakis L. Cram B. Chan 《Astrophysics and Space Science》2003,285(1):149-153
A strong evolution of galaxies is observed for 0<z<1, as evidenced by an increase of almost an order of magnitude in the galaxy star-formation rate density. However, it is known
that dust obscuration has affected our understanding of galaxy evolution over this significant fraction of the age of the
Universe. In order to study galaxy evolution free from dust induced biases, an ultra deep radio survey – the Phoenix Deep
Survey – was initiated. With a detection limit of 60μJy, this homogeneous survey, complemented with multiwavelength (photometric
and spectroscopic) observations, is being used to build a consistent picture of galaxy evolution. The ultra-deep radio source
counts are presented, and interpreted using luminosity function evolutionary models. The discovery of extremely dusty galaxies
from this survey, along with the clustering properties of the sub-mJy radio population, are also discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献