5,388 research outputs found
Bayesian analysis of the multivariate dependence of three transition water ecosystem classifications
The Water Framework Directive (WFD) recognizes benthic macroinvertebrates as a good biological quality element for transitional waters as they are the most exposed to natural variability patterns characteristic of these ecosystems, due to their life cycles and space-use behavior. Here, we address the ecological status classification issue for three lagoons in Apulia, using benthic macroinvertebrates and three proposed multimetric indices (namely M-AMBI, BITS and ISS), likely to respond differently to different sources of stress and natural variability. Lagoon classification is based on discretization by standard classification boundaries with only partial consideration of the natural variability of ecosystem properties and possible inaccuracies of the classification procedures. In order to investigate the possible contrasting behavior of the three classifications, we propose Bayesian hierarchical models in which the multimetric indices and their discrete counterparts are jointly modeled as function of abiotic covariates, external anthropogenic pressures indicators and spatio-temporal effects
Evolution in the iron abundance of the ICM
We present a Chandra analysis of the X-ray spectra of 56 clusters of galaxies
at , which cover a temperature range of keV. Our analysis
is aimed at measuring the iron abundance in the ICM out to the highest redshift
probed to date. We find that the emission-weighted iron abundance measured
within in clusters below 5 keV is, on average, a factor of
higher than in hotter clusters, following , which confirms the trend seen in local samples. We made use of
combined spectral analysis performed over five redshift bins at
to estimate the average emission weighted iron abundance. We find a constant
average iron abundance as a function of redshift,
but only for clusters at . The emission-weighted iron abundance is
significantly higher () in the redshift range
, approaching the value measured locally in the inner radii for a mix of cool-core and non cool-core clusters in the
redshift range . The decrease in with can be
parametrized by a power law of the form . The observed
evolution implies that the average iron content of the ICM at the present epoch
is a factor of larger than at . We confirm that the ICM is
already significantly enriched () at a look-back time
of 9 Gyr. Our data provide significant constraints on the time scales and
physical processes that drive the chemical enrichment of the ICM.Comment: 4 pages, 4 figures, to appear in the Proceedings of "The Extreme
Universe in the Suzaku Era", Dicember 2006, Kyoto (Japan
Tracing the evolution in the iron content of the ICM
We present a Chandra analysis of the X-ray spectra of 56 clusters of galaxies
at z>0.3, which cover a temperature range of 3>kT>15 keV. Our analysis is aimed
at measuring the iron abundance in the ICM out to the highest redshift probed
to date. We find that the emission-weighted iron abundance measured within
(0.15-0.3)R_vir in clusters below 5 keV is, on average, a factor of ~2 higher
than in hotter clusters, following Z(T)~0.88T^-(0.47)Z_o, which confirms the
trend seen in local samples. We made use of combined spectral analysis
performed over five redshift bins at 0.3>z>1.3 to estimate the average emission
weighted iron abundance. We find a constant average iron abundance Z_Fe~0.25Z_o
as a function of redshift, but only for clusters at z>0.5. The
emission-weighted iron abundance is significantly higher (Z_Fe~0.4Z_o) in the
redshift range z~0.3-0.5, approaching the value measured locally in the inner
0.15R_vir radii for a mix of cool-core and non cool-core clusters in the
redshift range 0.1<z<0.3. The decrease in Z_Fe with redshift can be
parametrized by a power law of the form ~(1+z)^(-1.25). The observed evolution
implies that the average iron content of the ICM at the present epoch is a
factor of ~2 larger than at z=1.2. We confirm that the ICM is already
significantly enriched (Z_Fe~0.25Z_o) at a look-back time of 9 Gyr. Our data
provide significant constraints on the time scales and physical processes that
drive the chemical enrichment of the ICM.Comment: 6 pages, 6 figures, to appear in the Proceedings of "Heating vs.
Cooling in Galaxies and Clusters of Galaxies", August 2006, Garching
(Germany
Discovery of a faint, star-forming, multiply lensed, Lyman-alpha blob
We report the discovery of a multiply lensed Lyman- blob (LAB) behind
the galaxy cluster AS1063 using the Multi Unit Spectroscopic Explorer (MUSE) on
the Very Large Telescope (VLT). The background source is at 3.117 and is
intrinsically faint compared to almost all previously reported LABs. We used
our highly precise strong lensing model to reconstruct the source properties,
and we find an intrinsic luminosity of =
erg s, extending to 33 kpc. We find that the LAB is associated with a
group of galaxies, and possibly a protocluster, in agreement with previous
studies that find LABs in overdensities. In addition to Lyman-
(Ly) emission, we find \ion{C}{IV}, \ion{He}{II}, and \ion{O}{III}]
ultraviolet (UV) emission lines arising from the centre of the nebula. We used
the compactness of these lines in combination with the line ratios to conclude
that the \Lya nebula is likely powered by embedded star formation. Resonant
scattering of the \Lya photons then produces the extended shape of the
emission. Thanks to the combined power of MUSE and strong gravitational
lensing, we are now able to probe the circumgalatic medium of sub-
galaxies at .Comment: 7 pages, 7 figures; moderate changes to match the accepted A&A
versoi
The sub-mJy radio sky in the Extended Chandra Deep Field South: source population
The sub-mJy radio population is a mixture of active systems, that is star
forming galaxies (SFGs) and active galactic nuclei (AGNs). We study a sample of
883 radio sources detected at 1.4 GHz in a deep Very Large Array survey of the
Extended Chandra Deep Field South (E-CDFS) that reaches a best rms sensitivity
of 6 microJy. We have used a simple scheme to disentangle SFGs, radio-quiet
(RQ), and radio-loud (RL) AGNs based on the combination of radio data with
Chandra X-ray data and mid-infrared observations from Spitzer. We find that at
flux densities between about 30 and 100 microJy the radio population is
dominated by SFGs (~60%) and that RQ AGNs become increasingly important over RL
ones below 100 microJy. We also compare the host galaxy properties of the three
classes in terms of morphology, optical colours and stellar masses. Our results
show that both SFG and RQ AGN host galaxies have blue colours and late type
morphology while RL AGNs tend to be hosted in massive red galaxies with early
type morphology. This supports the hypothesis that radio emission in SFGs and
RQ AGNs mainly comes from the same physical process: star formation in the host
galaxy.Comment: 13 pages, 11 figures, 1 table, accepted for publication in MNRA
The micro-Jy Radio Source Population: the VLA-CDFS View
We analyse the 267 radio sources from our deep (flux limit of 42 microJy at
the field center at 1.4 GHz) Chandra Deep Field South 1.4 and 5 GHz VLA survey.
The radio population is studied by using a wealth of multi-wavelength
information, including morphology and spectral types, in the radio, optical,
and X-ray bands. The availability of redshifts for ~ 70% of our sources allows
us to derive reliable luminosity estimates for the majority of the objects.
Contrary to some previous results, we find that star-forming galaxies make up
only a minority (~ 1/3) of sub-mJy sources, the bulk of which are faint radio
galaxies, mostly of the Fanaroff-Riley I type.Comment: 6 pages, 3 figures, to appear in the proceedings of "At the Edge of
the Universe", Sintra, Portugal, Oct. 9 - 13, 200
The Evolutionary Status of Clusters of Galaxies at z ~ 1
Combined HST, X-ray, and ground-based optical studies show that clusters of
galaxies are largely "in place" by , an epoch when the Universe was
less than half its present age. High resolution images show that elliptical,
S0, and spiral galaxies are present in clusters at redshifts up to . Analysis of the CMDs suggest that the cluster ellipticals formed their
stars several Gyr earlier, near redshift 3. The morphology--density relation is
well established at , with star-forming spirals and irregulars residing
mostly in the outer parts of the clusters and E/S0s concentrated in dense
clumps. The intracluster medium has already reached the metallicity of
present-day clusters. The distributions of the hot gas and early-type galaxies
are similar in clusters, indicating both have largely virialized in
the deepest potentials wells. In spite of the many similarities between
and present-day clusters, there are significant differences. The
morphologies revealed by the hot gas, and particularly the early-type galaxies,
are elongated rather than spherical. We appear to be observing the clusters at
an epoch when the sub-clusters and groups are still assembling into a single
regular cluster. Support for this picture comes from CL0152 where the gas
appears to be lagging behind the luminous and dark mass in two merging
sub-components. Moreover, the luminosity difference between the first and
second brightest cluster galaxies at is smaller than in 93% of
present-day Abell clusters, which suggests that considerable luminosity
evolution through merging has occurred since that epoch. Evolution is also seen
in the bolometric X-ray luminosity function.Comment: 18 pages, 12 figures, to appear in Penetrating Bars through Masks of
Cosmic Dust: the Hubble Tuing Fork Strikes a New Note, eds. D.L. Block, K.C.
Freeman, I. Puerari & R. Groess. Figures degraded to meet astroph size limit;
a version with higher resolution figures may be downloaded from:
http://acs.pha.jhu.edu/~jpb/z1clusters/ford_clusters.pd
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