Katherine Blundell OBE

Abstract:

We report the detection of extended X-ray emission around two powerful high-z radio galaxies (HzRGs) at z~3.6 (4C03.24 & 4C19.71) and use these to investigate the origin of extended, Inverse Compton (IC) powered X-ray halos at high z. The halos have X-ray luminosities of Lx~3e44 erg/s and sizes of ~60kpc. Their morphologies are broadly similar to the ~60-kpc long radio lobes around these galaxies suggesting they are formed from IC scattering by relativistic electrons in the radio lobes, of either CMB or FIR photons from the dust-obscured starbursts in these galaxies. These observations double the number of z>3 HzRGs with X-ray detected IC halos. We compare the IC X-ray to radio luminosity ratios for these new detections to the two previously detected z~3.8 HzRGs. Given the similar redshifts, we would expect comparable X-ray IC luminosities if CMB mm photons are the seed field for the IC emission. Instead the two z~3.6 HzRGs, which are ~4x fainter in the FIR, also have ~4x fainter X-ray IC emission. Including a further six z>2 radio sources with IC X-ray halos from the literature, we suggest that in the more compact (lobe sizes <100-200kpc), majority of radio sources, the bulk of the IC emission may be driven by scattering of locally produced FIR photons from luminous, dust-obscured starbursts within these galaxies, rather than CMB photons. The resulting X-ray emission can ionise the gas on ~100-200-kpc scales around these systems and thus form their extended Ly-alpha emission line halos. The starburst and AGN activity in these galaxies are thus combining to produce an effective and wide-spread "feedback" process, acting on the long-term gas reservoir for the galaxy. If episodic radio activity and co-eval starbursts are common in massive, high-z galaxies, then this IC-feedback mechanism may affect the star-formation histories of massive galaxies. [Abridged]

Abstract:

We present a 100ks Chandra observation studying the extended X-ray emission around the powerful z= 1.04 quasar PKS1229-021. The diffuse cluster X-ray emission can be traced out to ∼15arcsec (∼120kpc) radius and there is a drop in the calculated hardness ratio inside the central 5arcsec consistent with the presence of a cool core. Radio observations of the quasar show a strong core and a bright, one-sided jet leading to the south-west hotspot and a second hotspot visible on the counter-jet side. Although the wings of the quasar point spread function (PSF) provided a significant contribution to the total X-ray flux at all radii where the extended cluster emission was detected, we were able to accurately subtract the PSF emission using Chandra Ray Tracer and marx simulations. The resulting steep cluster surface brightness profile for PKS1229-021 appears similar to the profile for the FR II (Fanaroff-Riley class II) radio galaxy 3C444, which has a similarly rapid surface brightness drop caused by a powerful shock surrounding the radio lobes. Using a model surface brightness profile based on 3C444, we estimated the total cluster luminosity for PKS1229-021 to be. We discuss the difficulty of detecting cool-core clusters, which host bright X-ray sources, in high redshift surveys. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.