1,963 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
LOFAR, a new low frequency radio telescope
LOFAR, the Low Frequency Array, is a large radio telescope consisting of
approximately 100 soccer-field sized antenna stations spread over a region of
400 km in diameter. It will operate at frequencies from ~10 to 240 MHz, with a
resolution at 240 MHz of better than an arcsecond. Its superb sensitivity will
allow for studies of a broad range of astrophysical topics, including
reionisation, transient radio sources and cosmic rays, distant galaxies and
AGNs. In this contribution a status rapport of the LOFAR project and an
overview of the science case is presented.Comment: 6 Pages, including 1 postScript figure. To appear in the proceedings
of the conference "Radio Galaxies: Past, present and future", Leiden, 11-15
Nov 200
Identification of the brightest Ly\alpha\ emitters at z=6.6: implications for the evolution of the luminosity function in the re-ionisation era
Using wide field narrow-band surveys, we provide a new measurement of the
Lyman- Emitter (LAE) luminosity function (LF), which
constraints the bright end for the first time. We use a combination of archival
narrow-band NB921 data in UDS and new NB921 measurements in SA22 and
COSMOS/UltraVISTA, all observed with the Subaru telescope, with a total area of
deg. We exclude lower redshift interlopers by using broad-band
optical and near-infrared photometry and also exclude three supernovae with
data split over multiple epochs. Combining the UDS and COSMOS samples we find
no evolution of the bright end of the Ly LF between and ,
which is supported by spectroscopic follow-up, and conclude that sources with
\emph{Himiko}-like luminosity are not as rare as previously thought, with
number densities of Mpc. Combined with our
wide-field SA22 measurements, our results indicate a non-Schechter-like bright
end of the LF at and a different evolution of \emph{observed} faint and
bright LAEs. This differential evolution is also seen in the spectroscopic
follow-up of UV selected galaxies and is now also confirmed for Ly
emitters, and we argue that it may be an effect of re-ionisation. Using a
toy-model, we show that such differential evolution of the LF is expected,
since brighter sources are able to ionise their surroundings earlier, such that
Ly photons are able to escape. Our targets are excellent candidates for
detailed follow-up studies and provide the possibility to give a unique view on
the earliest stages in the formation of galaxies and re-ionisation process.Comment: 20 pages, main results shown in Fig. 6 and Fig. 7, accepted by MNRA
Resolving the obscuring torus in NGC 1068 with the power of infrared interferometry: Revealing the inner funnel of dust
We present new interferometric data obtained with MIDI (MID infrared
Interferometric instrument) for the Seyfert II galaxy NGC 1068, with an
extensive coverage of sixteen uv points. These observations resolve the nuclear
mid-infrared emission from NGC 1068 in unprecedented detail with a maximum
resolution of 7 mas. For the first time, sufficient uv points have been
obtained, allowing us to generate an image of the source using maximum entropy
image reconstruction. The features of the image are similar to those obtained
by modelling. We find that the mid-infrared emission can be represented by two
components, each with a Gaussian brightness distribution. The first, identified
as the inner funnel of the obscuring torus, is hot (800K), 1.35 parsec long,
and 0.45 parsec thick in FWHM at a PA=-42 degrees (from north to east). It has
an absorption profile different than standard interstellar dust and with
evidence for clumpiness. The second component is 3 by 4 pc in FWHM with T=300K,
and we identify it with the cooler body of the torus. The compact component is
tilted by 45 degrees with respect to the radio jet and has similar size and
orientation to the observed water maser distribution. We show how the dust
distribution relates to other observables within a few parsecs of the core of
the galaxy such as the nuclear masers, the radio jet, and the ionization cone.
We compare our findings to a similar study of the Circinus galaxy and other
relevant studies. Our findings shed new light on the relation between the
different parsec-scale components in NGC 1068 and the obscuring torus.Comment: Accepted to MNRA
Reionization and Cosmology with 21 cm Fluctuations
Measurement of the spatial distribution of neutral hydrogen via the
redshifted 21 cm line promises to revolutionize our knowledge of the epoch of
reionization and the first galaxies, and may provide a powerful new tool for
observational cosmology from redshifts 1<z<4 . In this review we discuss recent
advances in our theoretical understanding of the epoch of reionization (EoR),
the application of 21 cm tomography to cosmology and measurements of the dark
energy equation of state after reionization, and the instrumentation and
observational techniques shared by 21 cm EoR and post reionization cosmology
machines. We place particular emphasis on the expected signal and observational
capabilities of first generation 21 cm fluctuation instruments.Comment: Invited review for Annual Review of Astronomy and Astrophysics (2010
volume
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
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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