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Radio Observations (radio + observation)
Selected AbstractsWhere at a supermassive black hole do gamma-rays come from?ASTRONOMY & GEOPHYSICS, Issue 4 2009Article first published online: 20 JUL 200 Radio observations of galaxy M87 at the time of a massive gamma-ray flare have established that the gamma-ray emission arises close to the central black hole, in the inner jet. [source] The extraordinary radio galaxy MRC B1221,423: probing deeper at radio and optical wavelengthsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2010Helen M. Johnston ABSTRACT We present optical spectra and high-resolution multiwavelength radio observations of the compact steep-spectrum radio source MRC B1221,423 (z= 0.1706). MRC B1221,423 is a very young (,105 yr), powerful radio source which is undergoing a tidal interaction with a companion galaxy. We find strong evidence of interaction between the active galactic nucleus (AGN) and its environment. The radio morphology is highly distorted, showing a dramatic interaction between the radio jet and the host galaxy, with the jet being turned almost back on itself. H i observations show strong absorption against the nucleus at an infall velocity of ,250 km s,1 compared to the stellar velocity, as well as a second, broader component which may represent gas falling into the nucleus. Optical spectra show that star formation is taking place across the whole system. Broad optical emission lines in the nucleus show evidence of outflow. Our observations confirm that MRC B1221,423 is a young radio source in a gas-rich nuclear environment, and that there was a time delay of a few times 100 Myr between the onset of star formation and the triggering of the AGN. [source] Shock heating in the group atmosphere of the radio galaxy B2 0838+32AMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2008Nazirah N. Jetha ABSTRACT We present Chandra and radio observations, and analysis of Sloan Digital Sky Survey data, of the radio galaxy B2 0838+32A (4C 32.26) and its environment. The radio galaxy is at the centre of a nearby group that has often been identified with the cluster Abell 695, but we argue that the original Abell cluster is likely to be an unrelated and considerably more distant system. The radio source is a restarting radio galaxy and, using our Chandra data, we argue that the currently active lobes are expanding supersonically, driving a shock with Mach number 2.4+1.0,0.5 into the interstellar medium. This would be only the third strong shock round a young radio source to be discovered, after Centaurus A and NGC 3801. However, in contrast to both these systems, the host galaxy of B2 0838+32A shows no evidence for a recent merger, while the active galactic nuclei (AGN) spectrum shows no evidence for the dusty torus that would imply a large reservoir of cold gas close to the central black hole. On the contrary, the AGN spectrum is of a type that has been associated with the presence of a radiatively inefficient accretion flow that could be controlled by an AGN heating and subsequent cooling of the hot, X-ray emitting gas. If correct, this means that B2 0838+32A is the first source in which we can directly see entropy-increasing processes (shocks) driven by accretion from the hot phase of the interstellar medium. [source] Lensing of 21-cm absorption haloes of z, 2,30 first galaxiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2007Pengjie Zhang ABSTRACT Extended 21-cm absorption regions (dubbed ,21-cm absorption haloes') around first galaxies at z, 30 are likely the first distinctive structures accessible to radio observations. Though the radio array capable of detecting and resolving them must have ,200 km2 total collecting area, given the great impact of such detections to the understanding of the reionization process and cosmology, such radio survey would be extremely profitable. As an example, we point out a potentially useful byproduct of such survey. The resolved 21-cm absorption ,haloes', likely close to spherical, can serve as (almost) ideal sources for measuring the cosmic shear and mapping the matter distribution to z, 30. We investigate the expected lensing signal and consider a variety of noise contributions on the shear measurement. We find that signal-to-noise ratio (S/N) , 1 can be achieved for individual ,haloes'. Given millions of 21-cm absorption ,haloes' across the sky, the total S/N will be comparable to traditional shear measurement of ,109 galaxies at z, 1. [source] A sample of mJy radio sources at 1.4 GHz in the Lynx and Hercules fields , I. Radio imaging, multicolour photometry and spectroscopyMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007E. E. Rigby ABSTRACT With the goal of identifying high-redshift radio galaxies with Fanaroff,Riley class I (FR I) classification, here are presented high-resolution, wide-field radio observations, near-infrared and optical imaging and multi-object spectroscopy of two fields of the Leiden,Berkeley Deep Survey. These fields, Hercules.1 and Lynx.2, contain a complete sample of 81 radio sources with S1.4 GHz > 0.5 mJy within 0.6 deg2. This sample will form the basis for a study of the population and cosmic evolution of high-redshift, low-power, FR I radio sources which will be presented in Paper II. Currently, the host galaxy identification fraction is 86 per cent with 11 sources remaining unidentified at a level of r,, 25.2 mag (Hercules; four sources) or r,, 24.4 mag (Lynx; seven sources) or K, 20 mag. Spectroscopic redshifts have been determined for 49 per cent of the sample and photometric redshift estimates are presented for the remainder of the sample. [source] G315.1+2.7: a new Galactic supernova remnant from the AAO/UKST H, surveyMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007M. Stupar ABSTRACT New narrow-band H, imaging and subsequent optical spectra confirm G315.1+2.7, a previously identified candidate supernova remnant (SNR), as a bona fide Galactic SNR. Present observations are based on independent discovery of filamentary optical emission nebulosity on images of the Anglo-Australian Observatory/United Kingdom Schmidt Telescope H, survey of the southern Galactic plane which were found to coincide with existing multifrequency radio detections. Separate medium- and high-dispersion spectra were taken across two locations of this 11-arcmin north,south (NS) aligned optical filament. The resulting spectral signatures were found to strongly confirm the SNR identification based on standard emission-line ratio discriminators which characterize emission from shock-heated gas. The average observed ratios of S ii/H,= 1.13, N ii/H,= 1.43 and S ii 6717/6731 = 1.46, together with the simultaneous detection of [O ii] 3727, [O iii] 5007 and [O i] 6300 Å, all point to a SNR origin of the observed optical emission. There is also an excellent positional coincidence between the new H, filament and the north-east radio arc of G315.1+2.7 seen at several frequencies. Careful scrutiny of the low-resolution but high-sensitivity Southern H, Sky Survey Atlas also revealed a low-level but distinct optical emission arc. This arc precisely correlates with the large, 2.5°, NS angular extent of the proposed new SNR also seen as a fractured structure in the extant radio data. G315.1+2.7 was detected previously at 2400 and 4800 MHz and at 408 and 1420 MHz. We also identified associated radio emission at 843 MHz from the now publicly available Sydney University Molonglo Sky Survey. On the basis of optical imaging and spectra and radio observations at five frequencies, we identify G315.1+2.7 as a new Galactic SNR. The large projected angular extent of the new remnant, together with the distance estimate of ,1.7 kpc and diameter of ,80 pc, make G315.1+2.7 one of the largest remnants known. [source] 3C 254: MERLIN observations of a highly asymmetric quasarMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006P. Thomasson ABSTRACT Multifrequency, high-resolution radio observations of the quasar 3C 254 using the Multi-Element Radio-linked Interferometer Network (MERLIN) are presented. The quasar has a highly asymmetric radio structure, with the eastern component of the double-lobed structure being much closer to the nucleus and significantly less polarized than the western one. However, the two lobes are more symmetric in their total flux densities. The observations show the detailed structure of the hotspots which are very different on opposite sides of the radio core, reveal no radio jet and suggest that the oppositely directed jets may be intrinsically asymmetric. [source] Discovery of an unusual new radio source in the star-forming galaxy M82: faint supernova, supermassive black hole or an extragalactic microquasar?MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2010T. W. B. Muxlow ABSTRACT A faint new radio source has been detected in the nuclear region of the starburst galaxy M82 using Multi-Element Radio-Linked Interferometer Network radio observations designed to monitor the flux density evolution of the recent bright supernova SN 2008iz. This new source was initially identified in observations made between 2009 May 1 and 5 but had not been present in observations made 1 week earlier, or in any previous observations of M82. In this Letter, we report the discovery of this new source and monitoring of its evolution over its first 9 months of existence. The true nature of this new source remains unclear, and we discuss whether this source is an unusual and faint supernova, a supermassive black hole associated with the nucleus of M82 or intriguingly the first detection of radio emission from an extragalactic microquasar. [source] The radio expansion and brightening of the very young supernova remnant G1.9 + 0.3MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2008D. A. Green ABSTRACT Recent radio observations of the small Galactic supernova remnant G1.9 + 0.3 made at 4.86 GHz with the Very Large Array are presented, and compared with earlier observations at 1.49 GHz which have a comparable resolution (10 × 4 arcsec2). These show that the radio emission from this remnant has expanded significantly, by about 15 per cent over 23 yr, with a current outer diameter of ,92 arcsec. This expansion confirms that G1.9 + 0.3 is the youngest Galactic remnant yet identified, only about 150 yr old at most. Recent, lower resolution, 1.43-GHz observations are also discussed, and the integrated flux densities from these and the 4.86-GHz observations are compared with earlier results. This shows that the integrated flux density of G1.9 + 0.3 has been increasing recently. [source] Post-starburst galaxies and the transformation of blue into red galaxiesASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009S. De Rijcke Abstract We present deep single-dish radio observations of a sample of nearby post-starburst galaxies (0.05 < z < 0.1). About 50% of these post-starburst galaxies are detected at 21 cm, with HI masses of ,109 M,, up to ,1010 M,. These post-starburst galaxies are as gas-rich as spiral galaxies with comparable luminosities. There appears to exist no direct correlation between the amount of H I present in a post-starburst galaxy and its star formation rate as traced by radio continuum emission. Moreover, the end of the starburst clearly does not necessarily require the complete exhaustion of the neutral gas reservoir. High-resolution radio observations of one post-starburst binary system suggest that most of the neutral gas resides outside the stellar bodies of the galaxies. Most likely, the gas was expelled by supernova and/or AGN feedback. This effectively stops star formation, even though copious amounts of diffuse neutral gas remain in the immediate vicinity. This remaining H I reservoir may eventually lead to further episodes of star formation. This may indicate that some post-starbursts are observed in the inactive phase ofthe star formation duty cycle (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Antenna performance analysis for decameter solar radio observationsASTRONOMISCHE NACHRICHTEN, Issue 7 2009A.A. Stanislavsky Abstract Decameter wavelength radio emission is finely structured in solar bursts. For their research it is very important to use a sufficient sensitivity of antenna systems. In this paper we study an influence of the radiotelescope-antenna effective area on the results of decameter solar radio observations. For this purpose we compared the solar bursts received by the array of 720 ground-based dipoles and the single dipole of the radiotelescope UTR-2. It is shown that a larger effective area of the ground-based antenna allows us to measure a weaker solar emission and to distinguish a fine structure of strong solar events. This feature has been also verified by simultaneous ground- and space-based observations in the overlapping frequency range (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Observations of magnetic fields in regular and irregular clustersASTRONOMISCHE NACHRICHTEN, Issue 5-6 2006F. Govoni Abstract The existence of magnetic fields associated with the intracluster medium in clusters of galaxies is now well established through different methods of analysis. The most detailed evidence for the presence of cluster magnetic fields comes from radio observations. Magnetic fields can be investigated through the synchrotron emission of cluster-wide diffuse sources and from studies of the rotation measure of polarized radio galaxies. I will review efforts to measure magnetic field strengths and power spectra and the main issues that have led to our knowledge on magnetic fields in regular and irregular clusters of galaxies. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||