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Register a new userOn the Environment of Powerful Radio Galaxies at z>0.5
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E. Belsole
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Active galaxies are the most powerful engines in the Universe for converting gravitational energy into radiation, and radio galaxies and radio-loud quasars are highly luminous and can be detected across the Universe. The jets that characterise them need a medium to propagate into, and thus radio galaxies at high redshift point to gaseous atmospheres on scales of at least the radio source diameter, which in many cases can reach hundreds of kpc. The variation with redshift of X-ray properties of radio-selected clusters provides an important test of structure formation theories as, unlike X-ray selection, this selection is not biased towards the most luminous clusters in the Universe. We present new results from a sample of 19 luminous radio galaxies at redshifts between 0.5 and 1. The properties of the gaseous atmosphere around these sources as mapped by Chandra and XMM-Newton observations are discussed. By combining these with observations at radio frequency, we will be able to draw conclusions on cluster size, density, and pressure balance between the radio source and the environment in which it lies.
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We present near-infrared H-band imaging of 15 intermediate redshift (0.5<z<1) radio quiet quasars (RQQ) in order to characterize the properties of their host galaxies. We are able to clearly detect the surrounding nebulosity in 12 objects, whereas the object remains unresolved in three cases. For all the resolved objects, we find that the host galaxy is well represented by a de Vaucouleurs r^{1/4} surface brightness law. This is the first reasonably sized sample of intermediate redshift RQQs studied in the near-infrared. The RQQ host galaxies are luminous (average M_H=-26.3+-0.6) and large giant elliptical galaxies (average bulge scale length R_e = 11.3pm5.8 kpc). RQQ hosts are about 1 mag brighter than the typical low redshift galaxy luminosity L^*, and their sizes are similar to those of galaxies hosting lower redshift RQQs, indicating that there is no significant evolution at least up to z=1 of the host galaxy structure. We also find that RQQ hosts are about 0.5-1 mag fainter than radio-loud quasars (RLQ) hosts at the similar redshift range. The comparison of the host luminosity of intermediate redshift RQQ hosts with that for lower z sources shows a trend that is consistent with that expected from the passive evolution of the stars in the host galaxies. The nuclear luminosity and the nucleus/host galaxy luminosity ratio of the objects in our sample are intermediate between those of lower redshift RQQs and those of higher redshift (z>1) RQQs.
X-ray cluster emission has been observed mainly in clusters with inactive cD galaxies (L_bol ~1E40-1E43erg/sec), which do not show signs of accretion onto a SMBH. Our recent Chandra discovery of ~100kpc scale diffuse X-ray emission revealed the presence of an X-ray cluster associated with the radio loud quasar 3C186 at redshift z=1.1 and suggests interactions between the quasar and the cluster. In contrast to the majority of X-ray clusters the 3C186 cluster contains a quasar in the center whose radiative power alone exceeds that which would be needed to quench the cluster cooling. We present the Chandra X-ray data and new deep radio and optical images of this cluster. The 3C186 quasar is a powerful Compact Steep Spectrum radio source expanding into the cluster medium. The 2arcsec radio jet is unresolved in the Chandra observation, but its direction is orthogonal to the elliptical surface brightness of the cluster. The radio data show the possible presence of old radio lobes on 10 arcsec scale in the direction of the radio jet. We discuss the nature of this source in the context of intermittent radio activity and the interaction of the young expanding radio source with the cluster medium.
We present high angular resolution imaging ($23.9 times 11.3$ mas, $138.6 times 65.5$ pc) of the radio-loud quasar PSO~J352.4034$-$15.3373 at $z=5.84$ with the Very Long Baseline Array (VLBA) at 1.54 GHz. This quasar has the highest radio-to-optical flux density ratio at such a redshift, making it the radio-loudest source known to date at $z sim 6$. The VLBA observations presented here resolve this quasar into multiple components with an overall linear extent of 1.62 kpc ($0rlap{.}{}28$) and with a total flux density of $6.57 pm 0.38$ mJy, which is about half of the emission measured at a much lower angular resolution. The morphology of the source is comparable with either a radio core with a one-sided jet, or a compact or a medium-size Symmetric Object (CSO/MSO). If the source is a CSO/MSO, and assuming an advance speed of $0.2c$, then the estimated kinematic age is $sim 10^4$ yr.
Relic galaxies are thought to be the progenitors of high-redshift red nuggets that for some reason missed the channels of size growth and evolved passively and undisturbed since the first star formation burst (at $z>2$). These local ultracompact old galaxies are unique laboratories for studying the star formation processes at high redshift and thus the early stage of galaxy formation scenarios. Counterintuitively, theoretical and observational studies indicate that relics are more common in denser environments, where merging events predominate. To verify this scenario, we compared the number counts of a sample of ultracompact massive galaxies (UCMGs) selected within the third data release of the Kilo Degree Survey, that is, systems with sizes $R_{rm e} < 1.5 , rm kpc$ and stellar masses $M_{rm star} > 8 times 10^{10}, rm M_{odot}$, with the number counts of galaxies with the same masses but normal sizes in field and cluster environments. Based on their optical and near-infrared colors, these UCMGs are likely to be mainly old, and hence representative of the relic population. We find that both UCMGs and normal-size galaxies are more abundant in clusters and their relative fraction depends only mildly on the global environment, with denser environments penalizing the survival of relics. Hence, UCMGs (and likely relics overall) are not special because of the environment effect on their nurture, but rather they are just a product of the stochasticity of the merging processes regardless of the global environment in which they live.
We use the statistics of the VIPERS survey to investigate the relation between the surface mean stellar mass density Sigma=Mstar/(2*pi*Re^2) of massive passive galaxies (MPGs, Mstar>10^11 Msun) and their environment in the redshift range 0.5<z<0.8. Passive galaxies were selected on the basis of their NUVrK colors (~900 objects), and the environment was defined as the galaxy density contrast, delta, using the fifth nearest-neighbor approach. The analysis of Sigma vs. delta was carried out in two stellar mass bins. In galaxies with Mstar<2*10^11 Msun, no correlation between Sigma and delta is observed. This implies that the accretion of satellite galaxies, which is more frequent in denser environments and efficient in reducing the galaxy Sigma, is not relevant in the formation and evolution of these systems. Conversely, in galaxies with Mstar>2*10^11 Msun, we find an excess of MPGs with low Sigma and a deficit of high-Sigma MPGs in the densest regions wrt other environments. We interpret this result as due to the migration of some high-Sigma MPGs (<1% of the total population of MPGs) into low-Sigma MPGs, probably through mergers or cannibalism of small satellites. In summary, our results imply that the accretion of satellite galaxies has a marginal role in the mass-assembly history of most MPGs. We have previously found that the number density of VIPERS massive star-forming galaxies (MSFGs) declines rapidily from z=0.8 to z=0.5, which mirrors the rapid increase in the number density of MPGs. This indicates that the MSFGs at z>0.8 migrate to the MPG population. Here, we investigate the Sigma-delta relation of MSFGs at z>0.8 and find that it is consistent within 1 sigma with that of low-Sigma MPGs at z<0.8. Thus, the results of this and our previous paper show that MSFGs at z>0.8 are consistent in terms of number and environment with being the progenitors of low-Sigma MPGs at z<0.8.
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