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High-redshift Radio Galaxies (high-redshift + radio_galaxy)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

A sample of mJy radio sources at 1.4 GHz in the Lynx and Hercules fields , I. Radio imaging, multicolour photometry and spectroscopy

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
E. 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]

Ly, excess in high-redshift radio galaxies: a signature of star formation,

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
M. Villar-Martín
ABSTRACT About 54 per cent of radio galaxies at z, 3 and 8 per cent of radio galaxies at 2 ,z < 3 show unusually strong Ly, emission, compared with the general population of high-redshift (z, 2) radio galaxies. These Ly,-excess objects (LAEs) show Ly,/He ii values consistent with or above standard photoionization model predictions. We reject with confidence several scenarios to explain the unusual strength of Ly, in these objects: shocks, low nebular metallicities, high gas densities and absorption/scattering effects. We show that the most successful explanation is the presence of a young stellar population which provides the extra supply of ionizing photons required to explain the Ly, excess in at least the most extreme LAEs (probably in all of them). This interpretation is strongly supported by the tentative trend found by other authors for z, 3 radio galaxies to show lower ultraviolet rest-frame polarization levels, or the dramatic increase in the detection rate at submm wavelengths of z > 2.5 radio galaxies. The enhanced star formation activity in LAEs could be a consequence of a recent merger which has triggered both the star formation and the active galactic nucleus/radio activities. The measurement of unusually high Ly, ratios in the extended gas of some high-redshift radio galaxies suggests that star formation activity occurs in spatial scales of tens of kpc. We argue that, although the fraction of LAEs may be incompletely determined, both at 2 ,z < 3 and at z, 3, the much larger fraction of LAEs found at z, 3 is a genuine redshift evolution and not due to selection effects. Therefore, our results suggest that the radio galaxy phenomenon is more often associated with a massive starburst at z > 3 than at z < 3. [source]

Extended X-ray emission in the high-redshift quasar GB 1508+5714 at z= 4.3

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2003
W. Yuan
ABSTRACT We report the discovery of extended X-ray emission around the powerful high-redshift quasar GB 1508+5714 at z= 4.3, revealed in a long Chandra ACIS observation. The emission feature is 3,4 arcsec away from the quasar core, which corresponds to a projected distance of about 25 kpc. The X-ray spectrum is best fitted with a power law of photon index 1.92 ± 0.35 (90 per cent confidence limit). The X-ray flux and luminosity reach 9.2 × 10,15 erg cm,2 s,1 (0.5,8 keV) and 1.6 × 1045 erg s,1 (2.7,42.4 keV rest frame, ,,= 0.73, ,m= 0.27, H0= 71 km s,1 Mpc,1), which is about 2 per cent of the total X-ray emission of the quasar. We interpret the X-ray emission as inverse Compton scattering of cosmic microwave background photons. The scattering relativistic electron population could either be a quasi-static diffuse cloud fed by the jet, or an outer extension of the jet with a high bulk Lorentz factor. We argue that the lack of an obvious detection of radio emission from the extended component could be a consequence of Compton losses on the electron population, or of a low magnetic field. Extended X-ray emission produced by inverse Compton scattering may be common around high-redshift radio galaxies and quasars, demonstrating that significant power is injected into their surroundings by powerful jets. [source]

Extended X-ray emission from high-redshift radio galaxies

ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2006
C. S. Crawford
Abstract I review the observations, interpretation and implications of extended X-ray emission from powerful distant radio sources. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]