420 research outputs found
The pandemic pathogen of amphibians, Batrachochytrium dendrobatidis (Phylum Chytridiomycota), in Italy.
X-Ray Groups of Galaxies in the Aegis Deep and Wide Fields
We present the results of a search for extended X-ray sources and their
corresponding galaxy groups from 800-ks Chandra coverage of the All-wavelength
Extended Groth Strip International Survey (AEGIS). This yields one of the
largest X-ray selected galaxy group catalogs from a blind survey to date. The
red-sequence technique and spectroscopic redshifts allow us to identify 100
of reliable sources, leading to a catalog of 52 galaxy groups. The groups span
the redshift range and virial mass range
. For the 49 extended
sources which lie within DEEP2 and DEEP3 Galaxy Redshift Survey coverage, we
identify spectroscopic counterparts and determine velocity dispersions. We
select member galaxies by applying different cuts along the line of sight or in
projected spatial coordinates. A constant cut along the line of sight can cause
a large scatter in scaling relations in low-mass or high-mass systems depending
on the size of cut. A velocity dispersion based virial radius can more
overestimate velocity dispersion in comparison to X-ray based virial radius for
low mass systems. There is no significant difference between these two radial
cuts for more massive systems. Independent of radial cut, overestimation of
velocity dispersion can be created in case of existence of significant
substructure and also compactness in X-ray emission which mostly occur in low
mass systems. We also present a comparison between X-ray galaxy groups and
optical galaxy groups detected using the Voronoi-Delaunay method (VDM) for
DEEP2 data in this field.Comment: Accepted for publication in AP
The galaxy cluster Ysz-Lx and Ysz-M relations from the WMAP 5-yr data
We use multifrequency matched filters to estimate, in the WMAP 5-year data,
the Sunyaev-Zel'dovich (SZ) fluxes of 893 ROSAT NORAS/REFLEX clusters spanning
the luminosity range Lx,[0.1-2.4]keV = 2 10^{41} - 3.5 10^{45} erg s^{-1}. The
filters are spatially optimised by using the universal pressure profile
recently obtained from combining XMM-Newton observations of the REXCESS sample
and numerical simulations. Although the clusters are individually only
marginally detected, we are able to firmly measure the SZ signal (>10 sigma)
when averaging the data in luminosity/mass bins. The comparison between the
bin-averaged SZ signal versus luminosity and X-ray model predictions shows
excellent agreement, implying that there is no deficit in SZ signal strength
relative to expectations from the X-ray properties of clusters. Using the
individual cluster SZ flux measurements, we directly constrain the Y500-Lx and
Y500-M500 relations, where Y500 is the Compton y-parameter integrated over a
sphere of radius r500. The Y500-M500 relation, derived for the first time in
such a wide mass range, has a normalisation Y*500=[1.60 pm 0.19] 10^{-3}
arcmin^2 at M500=3 10^{14} h^{1} Msun, in excellent agreement with the X-ray
prediction of 1.54 10^{-3} arcmin^2, and a mass exponent of alpha=1.79 pm 0.17,
consistent with the self-similar expectation of 5/3. Constraints on the
redshift exponent are weak due to the limited redshift range of the sample,
although they are compatible with self-similar evolution.Comment: Version accepted for publication in Astronomy and Astrophysic
An exponential decline at the bright end of the z=6 galaxy luminosity function
We present the results of a search for the most luminous star-forming
galaxies at redshifts z~6 based on CFHT Legacy Survey data. We identify a
sample of 40 Lyman break galaxies brighter than magnitude z'=25.3 across an
area of almost 4 square degrees. Sensitive spectroscopic observations of seven
galaxies provide redshifts for four, of which only two have moderate to strong
Lyman alpha emission lines. All four have clear continuum breaks in their
spectra. Approximately half of the Lyman break galaxies are spatially resolved
in 0.7 arcsec seeing images, indicating larger sizes than lower luminosity
galaxies discovered with the Hubble Space Telescope, possibly due to on-going
mergers. The stacked optical and infrared photometry is consistent with a
galaxy model with stellar mass ~ 10^{10} solar masses. There is strong evidence
for substantial dust reddening with a best-fit A_V=0.7 and A_V>0.48 at 2 sigma
confidence, in contrast to the typical dust-free galaxies of lower luminosity
at this epoch. The spatial extent and spectral energy distribution suggest that
the most luminous z~6 galaxies are undergoing merger-induced starbursts. The
luminosity function of z=5.9 star-forming galaxies is derived. This agrees well
with previous work and shows strong evidence for an exponential decline at the
bright end, indicating that the feedback processes which govern the shape of
the bright end are occurring effectively at this epoch.Comment: 14 pages, 11 figures, AJ in press, revised to address referee
comment
Exploring the galaxy cluster-group transition regime at high redshifts: Physical properties of two newly detected z > 1 systems
Context: Multi-wavelength surveys for clusters of galaxies are opening a
window on the elusive high-redshift (z>1) cluster population. Well controlled
statistical samples of distant clusters will enable us to answer questions
about their cosmological context, early assembly phases and the thermodynamical
evolution of the intracluster medium. Aims: We report on the detection of two
z>1 systems, XMMU J0302.2-0001 and XMMU J1532.2-0836, as part of the XMM-Newton
Distant Cluster Project (XDCP) sample. We investigate the nature of the
sources, measure their spectroscopic redshift and determine their basic
physical parameters. Methods: The results of the present paper are based on the
analysis of XMM-Newton archival data, optical/near-infrared imaging and deep
optical follow-up spectroscopy of the clusters. Results: We confirm the X-ray
source XMMU J0302.2-0001 as a gravitationally bound, bona fide cluster of
galaxies at spectroscopic redshift z=1.185. We estimate its M500 mass to
(1.6+/-0.3) times 10^{14} Msun from its measured X-ray luminosity. This ranks
the cluster among intermediate mass system. In the case of XMMU J1532.2-0836 we
find the X-ray detection to be coincident with a dynamically bound system of
galaxies at z=1.358. Optical spectroscopy reveals the presence of a central
active galactic nucleus, which can be a dominant source of the detected X-ray
emission from this system. We provide upper limits of X-ray parameters for the
system and discuss cluster identification challenges in the high-redshift
low-mass cluster regime. A third, intermediate redshift (z=0.647) cluster, XMMU
J0302.1-0000, is serendipitously detected in the same field as XMMU
J0302.2-0001. We provide its analysis as well.Comment: Accepted to A&A, 13/04/2011. 15 pages, 18 figures, 5 tables, 2
appendice
Discovery of a high-z protocluster with tunable filters: the case of 6C0140+326 at z=4.4
We present the first results obtained using a tunable narrowband filter in
the search for high-z protoclusters. Using the recently commissioned red
tunable filter on the Gran Telescopio Canarias we have searched for Lya
emitters in a 75 arcmin^2 field centered on the z=4.413 radio galaxy
6C0140+326. With three different wavelength tunings we find a total of 27
unique candidate Lya emitters. The availability of three different wavelength
tunings allows us to make estimates of the redshifts for each of the objects.
It also allows us to separate a possible protocluster from structure in the
immediate foreground. This division shows that the foreground region contains
significantly fewer Lya emitters. Also, the spatial distribution of the objects
in the protocluster field deviates from a random distribution at the 2.5 sigma
level. The observed redshift distribution of the emitters is different from the
expected distribution of a blank field at the ~3 sigma level, with the Lya
emitters concentrated near the radio galaxy at z>4.38. The 6C0140+326 field is
denser by a factor of 9+/-5 than a blank field, and the number density of Lya
emitters close to the radio galaxy is similar to that of the z~4.1 protocluster
around TNJ1338-1942. We thus conclude that there is an overdensity of Lya
emitters around the radio galaxy 6C0140+326. This is one of few known
overdensities at such a high redshift.Comment: 10 pages, 6 figures, accepted for publication in MNRA
Comparison of the VIMOS-VLT Deep Survey with the Munich semi-analytical model. II. The colour-density relation up to z=1.5
[Abridged] We perform on galaxy mock catalogues the same colour-density
analysis made by Cucciati et al. (2006) on a 5 Mpc/h scale using the VVDS-Deep
survey, and compare the results from mocks with observed data. We use mocks
with the same flux limits (I=24) as the VVDS (CMOCKS), built using the semi-
analytic model by De Lucia & Blaizot (2007) applied to the Millennium
Simulation. From CMOCKS, we extracted samples of galaxies mimicking the VVDS
observational strategy (OMOCKS). We computed the B-band Luminosity Function LF
and the colour-density relation (CDR) in the mocks. We find that the LF in
mocks roughly agrees with the observed LF, but at z<0.8 the faint-end slope of
the model LF is steeper than the VVDS one. Computing the LF for early and late
type galaxies, we show that mocks have an excess of faint early-type and of
bright late-type galaxies with respect to data. We find that the CDR in OMOCKS
is in excellent agreement with the one in CMOCKS. At z~0.7, the CDR in mocks
agrees with the VVDS one (red galaxies reside mainly in high densities). Yet,
the strength of the CDR in mocks does not vary within 0.2<z<1.5, while the
observed relation flattens with increasing z and possibly inverts at z=1.3. We
argue that the lack of evolution in the CDR in mocks is not due only to
inaccurate prescriptions for satellite galaxies, but that also the treatment of
central galaxies has to be revised. The reversal of the CDR can be explained by
wet mergers between young galaxies, producing a starburst event. This should be
seen on group scales. A residual of this is found in observations at z=1.5 on
larger scales, but not in the mocks, suggesting that the treatment of physical
processes affecting satellites and central galaxies in models should be
revised.Comment: 15 pages, 12 figures, accepted for publication in A&
Islands within an island: Population genetic structure of the endemic Sardinian newt,Euproctus platycephalus
The identification of historic and contemporary barriers to dispersal is central to the conservation of endangered amphibians, but may be hindered by their complex life history and elusive nature. The complementary information generated by mitochondrial (mtDNA) and microsatellite markers generates a valuable tool in elucidating population structure and the impact of habitat fragmentation. We applied this approach to the study of an endangered montane newt, Euproctus platycephalus. Endemic to the Mediterranean island of Sardinia, it is threatened by anthropogenic activity, disease, and climate change. We have demonstrated a clear hierarchy of structure across genetically divergent and spatially distinct subpopulations. Divergence between three main mountain regions dominated genetic partitioning with both markers. Mitochondrial phylogeography revealed a deep division dating to ca. 1 million years ago (Mya), isolating the northern region, and further differentiation between the central and southern regions ca. 0.5 Mya, suggesting an association with Pleistocene severe glacial oscillations. Our findings are consistent with a model of southward range expansion during glacial periods, with postglacial range retraction to montane habitat and subsequent genetic isolation. Microsatellite markers revealed further strong population structure, demonstrating significant divergence within the central region, and partial differentiation within the south. The northern population showed reduced genetic diversity. Discordance between mitochondrial and microsatellite markers at this scale indicated a further complexity of population structure, in keeping with male-biased dispersal and female philopatry. Our study underscores the need to elucidate cryptic population structure in the ecology and conservation strategies for endangered island-restricted amphibians, especially in the context of disease and climate change
Galaxy clustering in the NEWFIRM Medium Band Survey: the relationship between stellar mass and dark matter halo mass at 1 < z < 2
We present an analysis of the clustering of galaxies as a function of their
stellar mass at 1 < z < 2 using data from the NEWFIRM Medium Band Survey
(NMBS). The precise photometric redshifts and stellar masses that the NMBS
produces allows us to define a series of mass limited samples of galaxies more
massive than 0.7, 1 and 3x10^10 Msun in redshift intervals centered on z = 1.1,
1.5 and 1.9 respectively. In each redshift interval we show that there exists a
strong dependence of clustering strength on the stellar mass limit of the
sample, with more massive galaxies showing a higher clustering amplitude on all
scales. We further interpret our clustering measurements in the LCDM
cosmological context using the halo model of galaxy clustering. We show that
the typical halo mass of central and satellite galaxies increases with stellar
mass, whereas the satellite fraction decreases with stellar mass, qualitatively
the same as is seen at z < 1. We see little evidence of any redshift dependence
in the stellar mass-to-halo mass relationship over our narrow redshift range.
However, when we compare with similar measurements at z~0, we see clear
evidence for a change in this relation. If we assume a universal baryon
fraction, the ratio of stellar mass to halo mass reveals the fraction of
baryons that have been converted to stars. We see that the peak in this star
formation efficiency for central galaxies shifts to higher halo masses at
higher redshift, moving from ~7x10^11 Msun at z~0 to ~3x10^12 Msun at z~1.5,
revealing evidence of `halo downsizing'. Finally we show that for highly biased
galaxy populations at z > 1 there may be a discrepancy between the measured
space density and clustering and that predicted by the halo model. This could
imply that there is a problem with one or more ingredients of the halo model at
these redshifts, for instance the halo bias relation or the halo profile.Comment: Accepted for publication in ApJ. Correction made to typo in halo
masses in conclusion
Coupling models of cattle and farms with models of badgers for predicting the dynamics of bovine tuberculosis (TB)
Bovine TB is a major problem for the agricultural industry in several
countries. TB can be contracted and spread by species other than cattle and
this can cause a problem for disease control. In the UK and Ireland, badgers
are a recognised reservoir of infection and there has been substantial
discussion about potential control strategies. We present a coupling of
individual based models of bovine TB in badgers and cattle, which aims to
capture the key details of the natural history of the disease and of both
species at approximately county scale. The model is spatially explicit it
follows a very large number of cattle and badgers on a different grid size for
each species and includes also winter housing. We show that the model can
replicate the reported dynamics of both cattle and badger populations as well
as the increasing prevalence of the disease in cattle. Parameter space used as
input in simulations was swept out using Latin hypercube sampling and
sensitivity analysis to model outputs was conducted using mixed effect models.
By exploring a large and computationally intensive parameter space we show that
of the available control strategies it is the frequency of TB testing and
whether or not winter housing is practised that have the most significant
effects on the number of infected cattle, with the effect of winter housing
becoming stronger as farm size increases. Whether badgers were culled or not
explained about 5%, while the accuracy of the test employed to detect infected
cattle explained less than 3% of the variance in the number of infected cattle
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