Astronomy and Astrophysics, volume 433, 87-100 (2005/4-1)
On the X-ray emission of z ∼2 radio galaxies: IC scattering of the CMB and no evidence for fully-formed potential wells.
OVERZIER R.A., HARRIS D.E., CARILLI C.L., PENTERICCI L., ROETTGERING H.J.A. and MILEY G.K.
Abstract (from CDS):
We present the results of 20ks Chandra observations for each of 5 radio galaxies in the redshift range 2.0<z<2.6. The goals were to (i) study the nature of their non-thermal X-ray emission; (ii) investigate the presence and amount of hot gas; and (iii) look for active galactic nuclei (AGN) overdensities in fields around high redshift radio galaxies. For 4 of the 5 targets we detect unresolved X-ray components coincident with the radio nuclei. From spectral analysis of one of the cores and comparison to the empirical radio to X-ray luminosity ratio (LR
) correlation for AGN, we find that the cores are underluminous in the X-rays indicating that obscuring material (n(HI)∼1022
) may be surrounding the nuclei. We detect X-ray emission coincident with the radio hotspots or lobes in 4 of the 5 targets. This extended emission can be explained by the Inverse-Compton (IC) scattering of photons that make up the cosmic microwave background (CMB). The magnetic field strengths of ∼100-200µG that we derive agree with the equipartition magnetic field strengths. The relative ease with which the lobe X-ray emission is detected is a consequence of the (1+z)4
increase in the energy density of the CMB. For one of the lobes, the X-ray emission could also be produced by a reservoir of hot, shocked gas. An HST image of the region around this radio component shows bright optical emission reminiscent of a bow-shock. By co-adding the 5 fields we created a deep, 100ks exposure to search for diffuse X-ray emission from thermal intra-cluster gas. We detect no diffuse emission and derive upper limits of ∼1044
erg/s, thereby ruling out a virialized structure of cluster-size scale at z∼2. The average number of soft X-ray sources in the field surrounding the radio sources is consistent with the number density of AGN in the Chandra Deep Fields, with only one of the fields showing a marginally statistically significant factor 2 excess of sources with f_0.5-2 keV_>3x10–15
erg/s/cm2. Analysis of the angular distribution of the field sources shows no evidence for large-scale structure associated with the radio galaxies, as was observed in the case of PKS 1138-262 by Pentericci et al. (2002A&A...396..109P
galaxies: high-redshift - galaxies: active - X-rays: galaxies: clusters - X-rays: general
p.91 1138-262 = LEDA 2826829, B0902+343 = GB6 B0902+3419, Table 1 0156-252 = [HB91] 0156-252, 0406-244 = LEDA 2823818, 0828+193 = GB6 B0828+1923, 2036-254 = LEDA 2830549, 2048-272 = 1Jy 2048-272
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