Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userHigh redshift FRII radio galaxies: X-ray properties of the cores
80
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present an extensive X-ray spectral analysis of the cores of 19 FRII sources in the redshift range 0.5<z<1.0 which were selected to be matched in isotropic radio power. The sample consists of 10 radio galaxies and 9 quasars. We compare our results with the expectations from a unification model that ascribes the difference between these two types of sources to the viewing angle to the line of sight, beaming and the presence of a dust and gas torus. We find that the spectrum of all the quasars can be fitted with a single power law, and that the spectral index flattens with decreasing angle to the line of sight. We interpret this as the effect of increasingly dominant inverse Compton X-ray emission, beamed such that the jet emission outshines other core components. For up to 70 per cent of the radio galaxies we detect intrinsic absorption; their core spectra are best fitted with an unabsorbed steep power law of average spectral index $Gamma=2.1$ and an absorbed power law of spectral index Gamma=1.6, which is flatter than that observed for radio-quiet quasars. We further conclude that the presence of a jet affects the spectral properties of absorbed nuclear emission in AGN. In radio galaxies, any steep-spectrum component of nuclear X-ray emission, similar to that seen in radio-quiet quasars, must be masked by a jet or by jet-related emission.
rate research
Read More
We investigate the properties of the environment around 20 powerful radio galaxies and quasars at redshifts between 0.45 and 1. Using XMM-Newton and Chandra observations we probe the spatial distribution and the temperature of the cluster gas. We find that more than 60 per cent of powerful radio sources in the redshift range of our sample lie in a cluster of X-ray luminosity greater than 10^44 erg/s, and all but one of the narrow-line radio galaxies, for which the emission from the nucleus is obscured by a torus, lie in a cluster environment. Within the statistical uncertainties we find no significant difference in the properties of the environment as a function of the orientation to the line of sight of the radio jet. This is in agreement with unification schemes. Our results have important implications for cluster surveys, as clusters around powerful radio sources tend to be excluded from X-ray and Sunyaev-Zeldovich surveys of galaxy clusters, and thus can introduce an important bias in the cluster luminosity function. Most of the radio sources are found close to pressure balance with the environment in which they lie, but the two low-excitation radio galaxies of the sample are observed to be under-pressured. This may be the first observational indication for the presence of non-radiative particles in the lobes of some powerful radio galaxies. We find that the clusters around radio sources in the redshift range of our sample have a steeper entropy-temperature relation than local clusters, and the slope is in agreement with the predictions of self-similar gravitational heating models for cluster gas infall. This suggests that selection by AGN finds systems less affected by AGN feedback than the local average.(Abridged)
We report spectral, imaging, and variability results from four new XMM-Newton observations and two new Chandra observations of high-redshift (z > 4) radio-loud quasars (RLQs). Our targets span lower, and more representative, values of radio loudness than those of past samples of high-redshift RLQs studied in the X-ray regime. Our spectral analyses show power-law X-ray continua with a mean photon index, Gamma =1.74 +/- 0.11, that is consistent with measurements of lower redshift RLQs. These continua are likely dominated by jet-linked X-ray emission, and they follow the expected anti-correlation between photon index and radio loudness. We find no evidence of iron Kalpha ~ emission lines or Compton-reflection continua. Our data also constrain intrinsic X-ray absorption in these RLQs. We find evidence for significant absorption (N_H ~ 10^22 cm^-2) in one RLQ of our sample (SDSS J0011+1446); the incidence of X-ray absorption in our sample appears plausibly consistent with that for high-redshift RLQs that have higher values of radio loudness. In the Chandra observation of PMN J221-2719 we detect apparent extended (~ 14 kpc) X-ray emission that is most likely due to a jet; the X-ray luminosity of this putative jet is ~2% that of the core. The analysis of a 4.9 GHz VLA image of PMN J221-2719 reveals a structure that matches the X-ray extension found in this source. We also find evidence for long-term (450-460 days) X-ray variability by 80-100% in two of our targets.
We describe the ensemble X-ray properties of high redshift clusters with emphasis on changes with respect to the local population. Cluster X-ray luminosity evolution is detected in five nearly independent surveys. The relevant issue now is characterizing this evolution. Cluster temperature evolution provides constraints on the dark matter and dark energy content of the universe. These constraints are complementary to and in agreement with those of the cosmic microwave background and supernovae, showing that the present universe is dominated by a dark energy. X-ray images show that most z > 0.75 clusters are not relaxed, hinting that the cluster formation epoch is z ~ 1.
(abridged) We firstly present the results of X-ray spectroscopic observations with XMM-Newton for four high-redshift radio-loud quasars at z>4. These observations more than double the number of z>4 radio-loud quasars having X-ray spectroscopic data to seven, which compose a significant subset of a flux-limited sample of z>4 radio-loud quasars. Based on this subset we show some preliminary results on the overall X-ray spectral properties of the sample. Soft X-ray spectral flattening, which is thought to arise from intrinsic X-ray absorption, was found in about half of the sample. We give a preliminary distribution of the absorption column density NH. For those with detected X-ray absorption, the derived NH values fall into a very narrow range (around a few times 10^(22)cm^(-2) for `cold absorption), suggesting a possible common origin of the absorber. Compared to lower-redshift samples at z<2, there is an extension, or a systematic shift, toward higher values in the intrinsic NH distribution at z>4, and an increase of the fraction of radio-loud quasars showing X-ray absorption toward high redshifts. These results indicate a cosmic evolution effect, which seems to be the strongest at redshifts around 2. The rest frame 1-50keV continua have photon indices with a mean of 1.64 and a standard deviation of 0.11. Variability appears to be common on timescales from a few months to years in the quasar rest-frame, sometimes in both fluxes and spectral slopes.
The very high rates of second generation star formation detected and inferred in high redshift objects should be accompanied by intense millimetre-wave emission from hot core molecules. We calculate the molecular abundances likely to arise in hot cores associated with massive star formation at high redshift, using several independent models of metallicity in the early Universe. If the number of hot cores exceeds that in the Milky Way Galaxy by a factor of at least one thousand, then a wide range of molecules in high redshift hot cores should have detectable emission. It should be possible to distinguish between independent models for the production of metals and hence hot core molecules should be useful probes of star formation at high redshift.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
