Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userVLA radio continuum observations of a new sample of high redshift radio galaxies
288
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present new deep multi-frequency radio-polarimetric images of a sample of high redshift radio galaxies (HzRGs), having redshift between 1.7 and 4.1. The radio data at 4.7 and 8.2 GHz were taken with the Very Large Array in the A configuration and provide a highest angular resolution of 0.2. Maps of total intensity, radio spectral index, radio polarization and internal magnetic field are presented for each source. The morphology of most objects is that of standard FRII double radio sources, but several contain multiple hot-spots in one or both lobes. Compared to similar samples of HzRGs previously imaged, there is a higher fraction (29%) of compact steep spectrum sources (i.e. sources with a projected linear size less than 20 kpc). Radio cores are identified in about half of the sample and tend to have relatively steep spectra (alpha < -1). Polarization is detected in all but 4 sources, with typical polarization at 8.2 GHz of around 10-20%. The Faraday rotation can be measured in most of the radio galaxies: the observed rotation measure (RM) of 8 radio sources exceeds 100 rad m^{-2} in at least one of the lobes, with large gradients between the two lobes. We find no dependence of Faraday rotation with other properties of the radio sources. If the origin of the Faraday rotation is local to the sources, as we believe, then the intrinsic RM is more than a 1000 rad m^{-2}. Because low redshift radio galaxies residing at the center of clusters usually show extreme RMs, we suggest that the high-z large RM sources also lie in very dense environments. Finally, we find that the fraction of powerful radio galaxies with extreme Faraday rotation increases with redshift, as would be expected if their average environment tends to become denser with decreasing cosmic epoch.
rate research
Read More
We present the results of a comprehensive Spitzer survey of 70 radio galaxies across 1<z<5.2. Using IRAC, IRS and MIPS imaging we determine the rest-frame AGN contribution to the stellar emission peak at 1.6um. The stellar luminosities are found to be consistent with that of a giant elliptical with a stellar mass of 10^11-12Msun. The mean stellar mass remains constant at ~10^11.5Msun up to z=3 indicating that the upper end of the mass function is already in place by this redshift. The mid-IR luminosities imply bolometric IR luminosities that would classify all sources as ULIRGs. The mid-IR to radio luminosity generally correlate implying a common origin for these emissions. The ratio is higher than that found for lower redshift, ie z<1, radio galaxies.
High redshift radio galaxies (HzRGs) are key targets for studies of the formation and evolution of massive galaxies. The role of dust in these processes is uncertain. We have therefore observed the dust continuum emission from a sample of z > 3 radio galaxies with the SCUBA bolometer array. We confirm and strengthen earlier results, that HzRGs are massive starforming systems and that submillimeter detection rate appears to be primarily a strong function of redshift. We also observed HzRG-candidates which have sofar eluded spectroscopic redshift determination. Four of these have been detected, and provide evidence that they may be extremely obscured radio galaxies, possibly in an early stage of their evolution.
We present the results of Karl G. Jansky Very Large Array (VLA) observations to study the properties of FR0 radio galaxies, the compact radio sources associated with early-type galaxies which represent the bulk of the local radio-loud AGN population. We obtained A-array observations at 1.5, 4.5, and 7.5 GHz for 18 FR0s from the FR0CAT sample: these are sources at $z<0.05$, unresolved in the FIRST images and spectroscopically classified as low excitation galaxies (LEG). Although we reach an angular resolution of $sim$0.3 arcsec, the majority of the 18 FR0s is still unresolved. Only four objects show extended emission. Six have steep radio spectra, 11 are flat cores, while one shows an inverted spectrum. We find that 1) the ratio between core and total emission in FR0s is $sim$30 times higher than in FRI and 2) FR0s share the same properties with FRIs from the nuclear and host point of view. FR0s differ from FRIs only for the paucity of extended radio emission. Different scenarios were investigated: 1) the possibility that all FR0s are young sources eventually evolving into extended sources is ruled out by the distribution of radio sizes; 2) similarly, a time-dependent scenario, where a variation of accretion or jet launching prevents the formation of large-scales radio structures, appears to be rather implausible due to the large abundance of sub-kpc objects 3) a scenario in which FR0s are produced by mildly relativistic jets is consistent with the data but requires observations of a larger sample to be properly tested.
Direct submm imaging has recently revealed the 850-micron background to be mostly composed of a population of distant ultraluminous infrared galaxies, but identifying the optical/NIR counterparts to these sources has proved difficult due to the poor submm spatial resolution. However, the proportionality of both cm and submm data to the star formation rate suggests that high resolution radio continuum maps with subarcsecond positional accuracy can be exploited to locate submm sources. In this paper we present results from a targeted SCUBA survey of micro-Jansky radio sources in the flanking fields of the Hubble Deep Field. Even with relatively shallow 850-micron SCUBA observations (>6 mJy at 3-sigma), we were successful at making submm detections of optical/NIR-faint (I>24 and K~21-22) radio sources, and our counts closely match the bright counts from submm surveys. Redshift estimates can be made from the ratio of the submm flux to the radio flux across the 100 GHz break in the spectral energy distribution. This millimetric redshift estimation places the bright submm population at z=1-3 where it forms the high redshift tail of the faint radio population. The star formation rate density (SFRD) due to ultraluminous infrared galaxies increases by more than two orders of magnitude from z~0 to z~1-3. The SFRD at high redshift inferred from our >6 mJy submm observations is comparable to that observed in the UV/optical. (Abridged)
We present the results of XMM-Newton observations of three high-redshift powerful radio galaxies 3C 184, 3C 292 and 3C 322. Although none of the sources lies in as rich an X-ray-emitting environment as is seen for some powerful radio galaxies at low redshift, the environments provide sufficient pressure to confine the radio lobes. The weak gas emission is particularly interesting for 3C 184, where a gravitational arc is seen, suggesting the presence of a massive cluster. Here Chandra data complement the XMM-Newton measurements by spatially separating X-rays from the extended atmosphere, the nucleus and the small-scale radio source. For 3C 292 the X-ray-emitting gas has a temperature of ~2 keV and luminosity of 6.5E43 erg/s, characteristic of a poor cluster. In all three cases, structures where the magnetic-field strength can be estimated through combining measurements of radio-synchrotron and inverse-Compton-X-ray emission, are consistent with being in a state of minimum total energy. 3C 184 and 3C 292 (and possibly 3C 322) have a heavily absorbed component of nuclear emission of N_H ~ $ few 10^{23} cm^{-2}.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
