1,397 research outputs found
Probing the Radio Loud/Quiet AGN dichotomy with quasar clustering
We investigate the clustering properties of 45441 radio-quiet quasars (RQQs)
and 3493 radio-loud quasars (RLQs) drawn from a joint use of the Sloan Digital
Sky Survey (SDSS) and Faint Images of the Radio Sky at 20 cm (FIRST) surveys in
the range . This large spectroscopic quasar sample allow us to
investigate the clustering signal dependence on radio-loudness and black hole
(BH) virial mass. We find that RLQs are clustered more strongly than RQQs in
all the redshift bins considered. We find a real-space correlation length of
and
{\normalsize{}for} RQQs and
RLQs, respectively, for the full redshift range. This implies that RLQs are
found in more massive host haloes than RQQs in our samples, with mean host halo
masses of and
, respectively. Comparison with
clustering studies of different radio source samples indicates that this mass
scale of is characteristic for the
bright radio-population, which corresponds to the typical mass of galaxy groups
and galaxy clusters. The similarity we find in correlation lengths and host
halo masses for RLQs, radio galaxies and flat-spectrum radio quasars agrees
with orientation-driven unification models. Additionally, the clustering signal
shows a dependence on black hole (BH) mass, with the quasars powered by the
most massive BHs clustering more strongly than quasars having less massive BHs.
We suggest that the current virial BH mass estimates may be a valid BH proxies
for studying quasar clustering. We compare our results to a previous
theoretical model that assumes that quasar activityComment: 15 pages, 13 figures, A&A in pres
A jet-cloud interaction in 3C34 at redshift z = 0.69
We report the detection of a strong jet-cloud interaction at a distance of
120 kpc from the nucleus of the radio galaxy 3C34, which has redshift z=0.69.
Hubble Space Telescope images of the radio galaxy show a long narrow region of
blue emission orientated along the radio axis and directed towards a radio
hotspot. The William Herschel Telescope has been used to provide long-slit
spectroscopic data of this object, and infrared observations made with the
United Kingdom InfraRed Telescope have enabled its spectral energy distribution
to be modelled. We propose that the aligned emission is associated with a
region of massive star-formation, induced by the passage of the radio jet
through a galaxy within the cluster surrounding 3C34. A star-formation rate of
about 100 solar masses per year is required, similar to the values necessary to
produce the alignment effect in high-redshift radio galaxies. The consequences
of this result for models of star formation in distant radio galaxies are
discussed.Comment: 12 pages including 11 figures, LaTeX. To appear in MNRA
Simulations of the Galaxy Cluster CIZA J2242.8+5301 I: Thermal Model and Shock Properties
The giant radio relic in CIZA J2242.8+5301 is likely evidence of a Mpc sized
shock in a massive merging galaxy cluster. However, the exact shock properties
are still not clearly determined. In particular, the Mach number derived from
the integrated radio spectrum exceeds the Mach number derived from the X-ray
temperature jump by a factor of two. We present here a numerical study, aiming
for a model that is consistent with the majority of observations of this galaxy
cluster. We first show that in the northern shock upstream X-ray temperature
and radio data are consistent with each other. We then derive progenitor masses
for the system using standard density profiles, X-ray properties and the
assumption of hydrostatic equilibrium. We find a class of models that is
roughly consistent with weak lensing data, radio data and some of the X-ray
data. Assuming a cool-core versus non-cool-core merger, we find a fiducial
model with a total mass of , a mass ratio of 1.76
and a Mach number that is consistent with estimates from the radio spectrum. We
are not able to match X-ray derived Mach numbers, because even low mass models
over-predict the X-ray derived shock speeds. We argue that deep X-ray
observations of CIZA J2242.8+5301 will be able to test our model and
potentially reconcile X-ray and radio derived Mach numbers in relics.Comment: 19 pages, 19 figure
Deep VLT spectroscopy of the z=2.49 Radio Galaxy MRC 2104-242: Evidence for a metallicity gradient in its extended emission line region
We present spectroscopic observations of the rest-frame UV line emission
around radio galaxy MRC 2104-242 at z=2.49, obtained with FORS1 on VLT Antu.
The morphology of the halo is dominated by two spatially resolved regions. Lya
is extended by >12 arcsec along the radio axis, CIV and HeII are extended by ~8
arcsec. The overall spectrum is typical for that of high redshift radio
galaxies. The most striking spatial variation is that NV is present in the
spectrum of the region associated with the center of the galaxy hosting the
radio source, the northern region, while absent in the southern region.
Assuming that the gas is photoionized by a hidden quasar, the difference in NV
emission can be explained by a metallicity gradient within the halo. This is
consistent with a scenario in which the gas is associated with a massive
cooling flow or originates from the debris of the merging of two or more
galaxies.Comment: Accepted for publication in A&A Letter
Multiple density discontinuities in the merging galaxy cluster CIZA J2242.8+5301
CIZA J2242.8+5301, a merging galaxy cluster at z=0.19, hosts a double-relic
system and a faint radio halo. Radio observations at frequencies ranging from a
few MHz to several GHz have shown that the radio spectral index at the outer
edge of the N relic corresponds to a shock of Mach number 4.6+/-1.1, under the
assumptions of diffusive shock acceleration of thermal particles in the test
particle regime. Here, we present results from new Chandra observations of the
cluster. The Chandra surface brightness profile across the N relic only hints
to a surface brightness discontinuity (<2-sigma detection). Nevertheless, our
reanalysis of archival Suzaku data indicates a temperature discontinuity across
the relic that is consistent with a Mach number of 2.5+/-0.5, in agreement with
previously published results. This confirms that the Mach number at the shock
traced by the N relic is much weaker than predicted from the radio. Puzzlingly,
in the Chandra data we also identify additional inner small density
discontinuities both on and off the merger axis. Temperature measurements on
both sides of the discontinuities do not allow us to undoubtedly determine
their nature, although a shock front interpretation seems more likely. We
speculate that if the inner density discontinuities are indeed shock fronts,
then they are the consequence of violent relaxation of the dark matter cores of
the clusters involved in the merger.Comment: 11 pages, 11 figures. Accepted for publication in MNRA
Cosmic downsizing of powerful radio galaxies to low radio luminosities
At bright radio powers ( W/Hz) the space density
of the most powerful sources peaks at higher redshift than that of their weaker
counterparts. This paper establishes whether this luminosity-dependent
evolution persists for sources an order of magnitude fainter than those
previously studied, by measuring the steep--spectrum radio luminosity function
(RLF) across the range W/Hz, out to high
redshift. A grid-based modelling method is used, in which no assumptions are
made about the RLF shape and high-redshift behaviour. The inputs to the model
are the same as in Rigby et al. (2011): redshift distributions from radio
source samples, together with source counts and determinations of the local
luminosity function. However, to improve coverage of the radio power vs.
redshift plane at the lowest radio powers, a new faint radio sample is
introduced. This covers 0.8 sq. deg., in the Subaru/XMM-Newton Deep Field, to a
1.4 GHz flux density limit of Jy, with 99%
redshift completeness. The modelling results show that the previously seen
high-redshift declines in space density persist to
W/Hz. At W/Hz the redshift of the peak space
density increases with luminosity, whilst at lower radio luminosities the
position of the peak remains constant within the uncertainties. This `cosmic
downsizing' behaviour is found to be similar to that seen at optical
wavelengths for quasars, and is interpreted as representing the transition from
radiatively efficient to inefficient accretion modes in the steep-spectrum
population. This conclusion is supported by constructing simple models for the
space density evolution of these two different radio galaxy classes; these are
able to successfully reproduce the observed variation in peak redshift.Comment: 7 pages, 6 figures; accepted for publication in Astronomy &
Astrophysic
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