274 research outputs found
Extended reagions of radio emission not associated with the AGN phenomenon as sources of acceleration of cosmic rays: The case of cD galaxies
Diffuse, non-thermal extended emission not associated with the AGN
phenomenon, found in many clusters of galaxies hosted by an AGN, are related to
the acceleration of cosmic rays. In the current work we present preliminary
evidence of absence of such formations in clusters of galaxies hosted by
optically identified cD galaxies. Our subsample consists of three powerful low
redshift radiogalaxies, centered in poor clusters of galaxies. We have searched
for radio relics and (mini)halos which could be forming as a result of the
confinement of cosmic rays by bubbles creayed by the AGN. We report on the work
in progress.Comment: 4 pages, Conference HEPRO II
HST images and properties of the most distant radio galaxies
We present Hubble Space Telescope images of 11 high redshift radio galaxies
(between and ). The galaxies were observed with the WFPC2 camera
in a broad band filter (F606W or F707W, roughly equivalent to V or R-band), for
2 orbits each. We find that on the scale of the HST observations there is a
wide variety of morphological structures of the hosting galaxies: most objects
have a clumpy, irregular appearance, consisting of a bright nucleus and a
number of smaller components, suggestive of merging systems. Some observed
structures could be due (at least partly) to the presence of dust distributed
through the galaxies. The UV continuum emission is generally elongated and
aligned with the axis of the radio sources, however the characteristics of the
``alignment effect'' differ from case to case, suggesting that the phenomenon
cannot be explained by a single physical mechanism. We compare the properties
of our radio galaxies with those of the
UV dropout galaxies and conclude that (i) the most massive radio galaxies may
well evolve from an aggregate of UV dropout galaxies and (ii) high redshift
radio galaxies probably evolve into present day brightest cluster galaxies.Comment: 22 pages, 30 figures, accepted by A&
Radiative Shock-Induced Collapse of Intergalactic Clouds
Accumulating observational evidence for a number of radio galaxies suggests
an association between their jets and regions of active star formation. The
standard picture is that shocks generated by the jet propagate through an
inhomogeneous medium and trigger the collapse of overdense clouds, which then
become active star-forming regions. In this contribution, we report on recent
hydrodynamic simulations of radiative shock-cloud interactions using two
different cooling models: an equilibrium cooling-curve model assuming solar
metallicities and a non-equilibrium chemistry model appropriate for primordial
gas clouds. We consider a range of initial cloud densities and shock speeds in
order to quantify the role of cooling in the evolution. Our results indicate
that for moderate cloud densities (>1 cm^{-3}) and shock Mach numbers (<20),
cooling processes can be highly efficient and result in more than 50% of the
initial cloud mass cooling to below 100 K. We also use our results to estimate
the final H_2 mass fraction for the simulations that use the non-equilibrium
chemistry package. This is an important measurement, since H_2 is the dominant
coolant for a primordial gas cloud. We find peak H_2 mass fractions of >0.01
and total H_2 mass fractions of >10^{-5} for the cloud gas. Finally, we compare
our results with the observations of jet-induced star formation in
``Minkowski's Object.'' We conclude that its morphology, star formation rate (~
0.3M_solar/yr) and stellar mass (~ 1.2 x 10^7 M_solar) can be explained by the
interaction of a 90,000 km/s jet with an ensemble of moderately dense (~ 10
cm^{-3}), warm (10^4 K) intergalactic clouds in the vicinity of its associated
radio galaxy at the center of the galaxy cluster.Comment: 30 pages, 7 figures, submitted to Astrophysical Journa
Implications of pc and kpc jet asymmetry to the cosmic ray acceleration
We probe the role that the directional asymmetry, between relativistic
outflows and kilo-parsec scale jets, play in the acceleration of cosmic rays.
For this reason we use two powerful, nearby Active Galactic Nuclei (AGNs).
These radio galaxies are atypical compared to the usual AGN as they contain
ring-like features instead of hotspots. Our VLBI radio data have revealed a
substantial misalignment between their small and large scale jets. Taking into
account the overall information we have obtained about the AGNs themselves (VLA
and VLBI radio data at 18 cm) and their clusters (X-ray observations) our study
supports the present ideas of powerful radiogalaxies (radio quiet and radio
loud) being sources of cosmic rays as well as their ability to accelarate the
latter to ultra high energies.Comment: 4 pages, Conference HEPRO II
Micro-costing study of rituximab subcutaneous injection versus intravenous infusion in dutch setting
The Nascent Red Sequence at z~2
We present new constraints on the evolution of the early-type galaxy
color-magnitude relation (CMR) based on deep near-infrared imaging of a galaxy
protocluster at z=2.16 obtained using NICMOS on-board the Hubble Space
Telescope. This field contains a spectroscopically confirmed space-overdensity
of Lyman-alpha and H-alpha emitting galaxies which surrounds the powerful radio
galaxy MRC 1138-262. Using these NICMOS data we identify a significant
surface-overdensity (= 6.2x) of red J-H galaxies in the color-magnitude diagram
(when compared with deep NICMOS imaging from the HDF-N and UDF). The
optical-NIR colors of these prospective red-sequence galaxies indicate the
presence of on-going dust-obscured star-formation or recently formed (<~ 1.5
Gyr)stellar populations in a majority of the red galaxies. We measure the slope
and intrinsic scatter of the CMR for three different red galaxy samples
selected by a wide color cut, and using photometric redshifts both with and
without restrictions on rest-frame optical morphology. In all three cases both
the rest-frame slope and intrinsic color scatter are considerably higher
than corresponding values for lower redshift galaxy clusters. These results
suggest that while some relatively quiescent galaxies do exist in this
protocluster both the majority of the galaxy population and hence the
color-magnitude relation are still in the process of forming, as expected.Comment: 8 pages, 7 figures, accepted for publication in ApJ (to appear June
1, 2008, v679n2
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