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Radio Luminosity (radio + luminosity)

Distribution by Scientific Domains

Physics and Astronomy	100%

Selected Abstracts

The environmental dependence of radio-loud AGN activity and star formation in the 2dFGRS

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2004
P. N. Best
ABSTRACT By combining the 2-degree Field Galaxy Redshift Survey with the NRAO VLA Sky Survey at 1.4 GHz, the environments of radio-loud active galactic nuclei (AGN) in the nearby Universe are investigated using both local projected galaxy densities and a friends-of-friends group-finding algorithm. Radio-loud AGN are preferentially located in galaxy groups and poor-to-moderate richness galaxy clusters. The AGN fraction appears to depend more strongly on the large-scale environment (group, cluster, etc.) in which a galaxy is located than on its more local environment, except at the lowest galaxy surface densities where practically no radio-loud AGN are found. The ratio of absorption-line to emission-line AGN changes dramatically with environment, with essentially all radio-loud AGN in rich environments showing no emission lines. This result could be connected with the lack of cool gas in cluster galaxies, and may have important consequences for analyses of optically selected AGN, which are invariably selected on emission-line properties. The local galaxy surface density of the absorption-line AGN is strongly correlated with radio luminosity, implying that the radio luminosities may be significantly boosted in dense environments due to confinement by the hot intracluster gas. The environments of a radio-selected sample of star-forming galaxies are also investigated to provide an independent test of optical studies. In line with those studies, the fraction of star-forming galaxies is found to decrease strongly with increasing local galaxy surface density; this correlation extends across the whole range of galaxy surface densities, with no evidence for the density threshold found in some optical studies. [source]

Environment and luminosity of supernova remnants

ASTRONOMISCHE NACHRICHTEN, Issue 5-6 2006
L. K. Hunt
Abstract The explosion of supernovae and the evolution of their remnants (SNRs) accelerate cosmic rays over a vast range of timescales. Magnetic fields can be investigated indirectly through one of the observational signatures of this acceleration, namely radio synchrotron emission. With the aim of better understanding the role of the magnetic field in supernova evolution, we explore the variation of SNR radio luminosities with physical conditions in the surrounding interstellar medium. With a data set that comprises more than 90 individual SNRs in 10 galaxies, and a range of 3000 in ISM density and 104 in radio synchrotron luminosity, we find a significant correlation between the two quantities. The observed trends support the hypothesis that adiabatic compression of magnetic fields by itself is insuf.cient to explain the radio emission of the brighter and more luminous in SNRs. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Radio imaging of the Subaru/XMM,Newton Deep Field , II.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2008
The 37 brightest radio sources
ABSTRACT We study the 37 brightest radio sources in the Subaru/XMM,Newton Deep Field. We have spectroscopic redshifts for 24 of 37 objects and photometric redshifts for the remainder, yielding a median redshift zmed for the whole sample of zmed, 1.1 and a median radio luminosity close to the ,Fanaroff,Riley type I/type II (FR I/FR II)' luminosity divide. Using mid-infrared (mid-IR) (Spitzer MIPS 24 ,m) data we expect to trace nuclear accretion activity, even if it is obscured at optical wavelengths, unless the obscuring column is extreme. Our results suggest that above the FR I/FR II radio luminosity break most of the radio sources are associated with objects that have excess mid-IR emission, only some of which are broad-line objects, although there is one clear low-accretion-rate object with an FR I radio structure. For extended steep-spectrum radio sources, the fraction of objects with mid-IR excess drops dramatically below the FR I/FR II luminosity break, although there exists at least one high-accretion-rate ,radio-quiet' QSO. We have therefore shown that the strong link between radio luminosity (or radio structure) and accretion properties, well known at z, 0.1, persists to z, 1. Investigation of mid-IR and blue excesses shows that they are correlated as predicted by a model in which, when significant accretion exists, a torus of dust absorbs ,30 per cent of the light, and the dust above and below the torus scatters ,1 per cent of the light. [source]

High-resolution observations of SN 2001gd in NGC 5033

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2005
M. A. Pérez-Torres
ABSTRACT We report on 8.4-GHz very-long-baseline interferometry (VLBI) observations of SN 2001gd in the spiral galaxy NGC 5033 made on 2002 June 26 (2002.48) and 2003 April 8 (2003.27). We used the interferometric visibility data to estimate angular diameter sizes for the supernova by model fitting. Our data nominally suggest a relatively strong deceleration for the expansion of SN 2001gd, but we cannot dismiss the possibility of a free supernova expansion. From our VLBI observations on 2003 April 8, we inferred a minimum total energy in relativistic particles and magnetic fields in the supernova shell of Emin= (0.3,14) × 1047 erg, and a corresponding equipartition average magnetic field of Bmin= 50,350 mG. We also present multiwavelength Very Large Array (VLA) measurements of SN 2001gd made at our second VLBI epoch at frequencies of 1.4, 4.9, 8.4, 15.0, 22.5 and 43.3 GHz. The VLA data are well fitted by an optically thin, synchrotron spectrum (,=,1.0 ± 0.1; S,,,,), partially absorbed by thermal plasma. We obtain a supernova flux density of 1.02 ± 0.05 mJy at the observing frequency of 8.4 GHz for the second epoch, which results in an isotropic radio luminosity of (6.0 ± 0.3) × 1036 erg s,1 between 1.4 and 43.3 GHz, at an adopted distance of 13.1 Mpc. Finally, we report on an XMM,Newton X-ray detection of SN 2001gd on 2002 December 18. The supernova X-ray spectrum is consistent with optically thin emission from a soft component (associated with emission from the reverse shock) at a temperature of around 1 keV. The observed flux corresponds to an isotropic X-ray luminosity of LX= (1.4 ± 0.4) × 1039 erg s,1 in the 0.3,5 keV band. We suggest that both radio and X-ray observations of SN 2001gd indicate that a circumstellar interaction similar to that displayed by SN 1993J in M 81 is taking place. [source]

The environmental dependence of radio-loud AGN activity and star formation in the 2dFGRS

Limits on radio emission from pulsar wind nebulae

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2000
B. M. Gaensler
We report on a sensitive survey for radio pulsar wind nebulae (PWN) towards 27 energetic and/or high-velocity pulsars. Observations were carried out at 1.4 GHz using the Very Large Array and the Australia Telescope Compact Array and utilized pulsar-gating to search for off-pulse emission. These observing parameters resulted in a considerably more sensitive search than previous surveys and could detect PWN over a much wider range of spatial scales (and hence ambient densities and pulsar velocities). However, no emission clearly corresponding to a PWN was discovered. Based on these non-detections we argue that the young and energetic pulsars in our sample have winds which are typical of young pulsars, but produce unobservable PWN because they reside in low-density (n,0.003 cm,3) regions of the interstellar medium. However, non-detection of PWN around older and less energetic pulsars can only be explained if the radio luminosity of their winds is less than 10,5 of their spin-down luminosity, implying an efficiency at least an order of magnitude smaller than that seen for young pulsars. [source]

The pulsar synchrotron: coherent radio emission

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2009
I. Contopoulos
ABSTRACT We propose a simple physical picture for the generation of coherent radio emission in the axisymmetric pulsar magnetosphere that is quite different from the canonical paradigm of radio emission coming from the magnetic polar caps. In this first paper, we consider only the axisymmetric case of an aligned rotator. Our picture capitalizes on an important element of the magnetohydrodynamic (MHD) representation of the magnetosphere, namely the separatrix between the corotating closed-line region (the ,dead zone') and the open-field lines that originate in the polar caps. Along the separatrix flows the return current that corresponds to the main magnetospheric electric current emanating from the polar caps. Across the separatrix, both the toroidal and poloidal components of the magnetic field change discontinuously. The poloidal component discontinuity requires the presence of a significant annular electric current which has up to now been unaccounted for. We estimate the position and thickness of this annular current at the tip of the closed line region, and show that it consists of electrons (positrons) corotating with Lorentz factors on the order of 105, emitting incoherent synchrotron radiation that peaks in the hard X-rays. These particles stay in the region of highest annular current close to the equator for a path-length of the order of 1 m. We propose that, at wavelengths comparable to that path-length, the particles emit coherent radiation, with radiated power proportional to N2, where N is the population of particles in the above path-length. We calculate the total radio power in this wavelength regime and its scaling with pulsar period and stellar magnetic field and show that it is consistent with estimates of radio luminosity based on observations. [source]

A survey of Low Luminosity Compact sources

ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009
M. Kunert-Bajraszewska
Abstract Based on the FIRST and SDSS catalogues a flux density limited sample of weak Compact Steep Spectrum (CSS) sources with radio luminosity below 1026WHz,1 at 1.4 GHz has been constructed. Our previous multifrequency observations of CSS sources have shown that low luminosity small-scale objects can be strong candidates for compact faders. This finding supports the idea that some small-size radio sources are short-lived phenomena because of a lack of significant fuelling. They never ,grow up' to become FRI or FRII objects. This new sample marks the start of a systematic study of the radio properties and morphologies of the population of low luminosity compact (LLC) objects. An investigation of this new sample should also lead to a better understanding of compact faders. In this paper, the results of the first stage of the new project , the L-band MERLIN observations of 44 low luminosity CSS sources are presented (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Evolution of radio galaxies

ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009
C.R. Kaiser
Abstract The dynamical evolution of FRII-type radio galaxies can be successfully modelled employing purely analytical techniques. The solutions change depending on the lobe size relative to the characteristic length scale for individual objects, resulting in three distinct regimes. By far the best understood regime is that of large sources. For these we can also construct emission models predicting the evolution of the radio luminosity as a function of source size or age and a limited number of source parameters. We can use such models to constrain the evolution of the radio galaxy population as a whole. Building on these successes, we find some hints that radio galaxies can change their morphologies between the two FR classes. Better emission models for all length scales and models for FRI-type objects are now needed to progress our understanding of all evolutionary branches of radio galaxies (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]