98 research outputs found
The galaxy luminosity function in the cluster of galaxies Abell 496
We have derived the galaxy luminosity function (GLF) in the cluster of
galaxies Abell 496 from a wide field image in the I band. A single Schechter
function reproduces quite well the GLF in the 17 <= I_{AB} <= 22 (-19.5 <= M_I
<= -14.5) magnitude interval, and the power law index of this function is found
to be somewhat steeper in the outer regions than in the inner regions. This
result agrees with the idea that faint galaxies are more abundant in the outer
regions of clusters, while in the denser inner regions they have partly been
accreted by larger galaxies or have been dimmed or even disrupted by tidal
interactions.Comment: Accepted for publication in Astronomy & Astrophysics, final versio
The merging cluster of galaxies Abell 3376: an optical view
Abell 3376 is a merging cluster of galaxies at redshift z=0.046, famous
mostly for its giant radio arcs, and shows an elongated and highly
substructured X-ray emission, but has not been analysed in detail at optical
wavelengths. We have obtained wide field images of Abell 3376 in the B band and
derive the GLF applying a statistical subtraction of the background in three
regions: a circle of 0.29 deg radius (1.5 Mpc) encompassing the whole cluster,
and two circles centered on each of the two brightest galaxies (BCG2,
northeast, coinciding with the peak of X-ray emission, and BCG1, southwest) of
radii 0.15 deg (0.775 Mpc). We also compute the GLF in the zone around BCG1,
which is covered by the WINGS survey in the B and V bands, by selecting cluster
members in the red sequence in a (B-V) versus V diagram. Finally, we discuss
the dynamical characteristics of the cluster implied by a Serna & Gerbal
analysis. The GLFs are not well fit by a single Schechter function, but
satisfactory fits are obtained by summing a Gaussian and a Schechter function.
The GLF computed by selecting galaxies in the red sequence in the region
surrounding BCG1 can also be fit by a Gaussian plus a Schechter function. An
excess of galaxies in the brightest bins is detected in the BCG1 and BCG2
regions. The dynamical analysis based on the Serna & Gerbal method shows the
existence of a main structure of 82 galaxies which can be subdivided into two
main substructures of 25 and 6 galaxies. A smaller structure of 6 galaxies is
also detected. The B band GLFs of Abell 3376 are clearly perturbed, as already
found in other merging clusters. The dynamical properties are consistent with
the existence of several substructures, in agreement with a previously
published X-ray analysis.Comment: 11 pages, 12 figures, accepted for publication in A&
Deep Spectroscopy of the Host Galaxy of a Tidal Disruption Flare in A1795
A likely tidal disruption of a star by the intermediate-mass black hole
(IMBH) of a dwarf galaxy was recently identified in association with Abell
1795. Without deep spectroscopy for this very faint object, however, the
possibility of a more massive background galaxy or even a disk-instability
flare from a weak AGN could not be dismissed. We have now obtained 8 hours of
Gemini spectroscopy which unambiguously demonstrate that the host galaxy is
indeed an extremely low-mass
galaxy in Abell 1795, comparable to the least-massive galaxies determined to
host IMBHs via other studies. We find that the spectrum is consistent with the
X-ray flare being due to a tidal disruption event rather than an AGN flare. We
also set improved limits on the black hole mass and infer a 15-year X-ray variability of a factor
of . The confirmation of this galaxy-black hole system provides a
glimpse into a population of galaxies that is otherwise difficult to study, due
to the galaxies' low masses and intrinsic faintness, but which may be important
contributors to the tidal disruption rate.Comment: 9 pages, 4 figures. Accepted by MNRA
A weak lensing study of the Coma cluster
Due to observational constraints, dark matter determinations in nearby
clusters based on weak lensing are still extremely rare, in spite of their
importance for the determination of cluster properties independent of other
methods. We present a weak lensing study of the Coma cluster (redshift 0.024)
based on deep images obtained at the CFHT. After obtaining photometric
redshifts for the galaxies in our field based on deep images in the u (1x1
deg2), and in the B, V, R and I bands (42'x52'), allowing us to eliminate
foreground galaxies, we apply weak lensing calculations on shape measurements
performed in the u image. We derive a map of the mass distribution in Coma, as
well as the radial shear profile, and the mass and concentration parameter at
various radii. We obtain M_200c = 5.1+4.3-2.1 x10^14 Msun and
c_200c=5.0+3.2-2.5, in good agreement with previous measurements. With deep
wide field images it is now possible to analyze nearby clusters with weak
lensing techniques, thus opening a broad new field of investigation
Weak lensing study of 16 DAFT/FADA clusters: substructures and filaments
While our current cosmological model places galaxy clusters at the nodes of a
filament network (the cosmic web), we still struggle to detect these filaments
at high redshifts. We perform a weak lensing study for a sample of 16 massive,
medium-high redshift (0.4<z<0.9) galaxy clusters from the DAFT/FADA survey,
that are imaged in at least three optical bands with Subaru/Suprime-Cam or
CFHT/MegaCam. We estimate the cluster masses using an NFW fit to the shear
profile measured in a KSB-like method, adding our contribution to the
calibration of the observable-mass relation required for cluster abundance
cosmological studies. We compute convergence maps and select structures within,
securing their detection with noise re-sampling techniques. Taking advantage of
the large field of view of our data, we study cluster environment, adding
information from galaxy density maps at the cluster redshift and from X-ray
images when available. We find that clusters show a large variety of weak
lensing maps at large scales and that they may all be embedded in filamentary
structures at megaparsec scale. We classify them in three categories according
to the smoothness of their weak lensing contours and to the amount of
substructures: relaxed (~7%), past mergers (~21.5%), recent or present mergers
(~71.5%). The fraction of clusters undergoing merging events observationally
supports the hierarchical scenario of cluster growth, and implies that massive
clusters are strongly evolving at the studied redshifts. Finally, we report the
detection of unusually elongated structures in CLJ0152, MACSJ0454, MACSJ0717,
A851, BMW1226, MACSJ1621, and MS1621.Comment: 25 pages, accepted for publication in A&
The cosmological analysis of X-ray cluster surveys: II- Application of the CR-HR method to the XMM archive
We have processed 2774 high-galactic observations from the XMM archive (as of
May 2010) and extracted a serendipitous catalogue of some 850 clusters of
galaxies based on purely X-ray criteria, following the methodology developed
for the XMM-LSS survey. Restricting the sample to the highest signal-to-noise
objects (347 clusters), we perform a cosmological analysis using the X-ray
information only. The analysis consists in the modelling of the observed
colour-magnitude (CR-HR) diagram constructed from cluster instrumental
count-rates measured in the [0.5-2], [1-2] and [0.5-1] keV bands. A MCMC
procedure simultaneously fits the cosmological parameters, the evolution of the
cluster scaling laws and the selection effects. Our results are consistent with
the sigma_8 and Omega_m values obtained by WMAP-5 and point toward a negative
evolution of the cluster scaling relations with respect to the self-similar
expectation. We are further able to constrain the cluster fractional radius
xc0=r_c/r500c, to xc0=0.24 +/- 0.04. This study stresses again the critical
role of selection effects in deriving cluster scaling relations, even in the
local universe. Finally, we show that CR-HR method applied to the eRosita
all-sky survey - provided that cluster photometric redshifts are available -
will enable the determination of the equation of state of the dark energy at
the level of the DETF stage IV predictions; simultaneously, the evolution of
the cluster scaling-relations will be unambiguously determined. The XMM CLuster
Archive Super Survey (XCLASS) serendipitous cluster catalogue is available
online at: http://xmm-lss.in2p3.fr:8080/l4sdb/.Comment: 26 pages, 24 figures, 9 tables. Accepted for publication in MNRAS
(minor changes with respect to submitted version). The corresponding galaxy
cluster catalogue is available at http://xmm-lss.in2p3.fr:8080/l4sdb
The XXL Survey V: Detection of the Sunyaev-Zel'dovich effect of the Redshift 1.9 Galaxy Cluster XLSSU J021744.1-034536 with CARMA
We report the detection of the Sunyaev-Zel'dovich (SZ) effect of galaxy
cluster XLSSU J021744.1-034536, using 30 GHz CARMA data. This cluster was
discovered via its extended X-ray emission in the XMM-Newton Large Scale
Structure survey, the precursor to the XXL survey. It has a photometrically
determined redshift , making it among the most distant
clusters known, and nominally the most distant for which the SZ effect has been
measured. The spherically integrated Comptonization is
, a measurement which is relatively
insensitive to assumptions regarding the size and redshift of the cluster, as
well as the background cosmology. Using a variety of locally calibrated cluster
scaling relations extrapolated to z~2, we estimate a mass - from the X-ray flux and SZ signal. The measured
properties of this cluster are in good agreement with the extrapolation of an
X-ray luminosity-SZ effect scaling relation calibrated from clusters discovered
by the South Pole Telescope at higher masses and lower redshifts. The full
XXL-CARMA sample will provide a more complete, multi-wavelength census of
distant clusters in order to robustly extend the calibration of cluster scaling
relations to these high redshifts.Comment: ApJ, in press. 9 pages, 4 figures, 4 table
The evolution of the cluster optical galaxy luminosity function between z=0.4 and 0.9 in the DAFT/FADA survey
We compute optical galaxy luminosity functions (GLFs) in the B, V, R, and I
rest-frame bands for one of the largest medium-to-high-redshift (0.4 < z < 0.9)
cluster samples to date in order to probe the abundance of faint galaxies in
clusters. We also study how the GLFs depend on cluster redshift, mass, and
substructure, and compare the GLFs of clusters with those of the field. We
separately investigate the GLFs of blue and red-sequence (RS) galaxies to
understand the evolution of different cluster populations. We find that the
shapes of our GLFs are similar for the B, V, R, and I bands with a drop at the
red GLF faint end that is more pronounced at high-redshift: alpha(red) ~ -0.5
at 0.40 0.1 at 0.65 < z < 0.90. The blue GLFs have
a steeper faint end (alpha(blue) ~ -1.6) than the red GLFs, that appears to be
independent of redshift. For the full cluster sample, blue and red GLFs
intersect at M(V) = -20, M(R) = -20.5, and M(I) = -20.3. A study of how galaxy
types evolve with redshift shows that late type galaxies appear to become early
types between z ~ 0.9 and today. Finally, the faint ends of the red GLFs of
more massive clusters appear to be richer than less massive clusters, which is
more typical of the lower redshift behaviour. Our results indicate that our
clusters form at redshifts higher than z = 0.9 from galaxy structures that
already have an established red sequence. Late type galaxies then appear to
evolve into early types, enriching the red-sequence between this redshift and
today. This effect is consistent with the evolution of the faint end slope of
the red-sequence and the galaxy type evolution that we find. Finally, faint
galaxies accreted from the field environment at all redshifts might have
replaced the blue late type galaxies that converted into early types,
explaining the lack of evolution in the faint end slopes of the blue GLFs.Comment: accepted for publication in A&
The XMM-LSS survey. Survey design and first results
We have designed a medium deep large area X-ray survey with XMM - the XMM
Large Scale Structure survey, XMM-LSS - with the scope of extending the
cosmological tests attempted using ROSAT cluster samples to two redshift bins
between 0<z<1 while maintaining the precision of earlier studies. Two main
goals have constrained the survey design: the evolutionary study of the
cluster-cluster correlation function and of the cluster number density. The
results are promising and, so far, in accordance with our predictions as to the
survey sensitivity and cluster number density. The feasibility of the programme
is demonstrated and further X-ray coverage is awaited in order to proceed with
a truly significant statistical analysis. (Abridged)Comment: Published in Journal of Cosmology and Astroparticle Physic
Surgical gastrostomy: current indications and complications in a university hospital
OBJECTIVE: To analyze the surgical gastrostomies performed at a public University Hospital, their indications and complications. METHODS: We conducted a retrospective, nonrandomized review of medical records of patients who underwent surgical gastrostomy from 2007 to 2011; RESULTS: , In the period of studied, 86 patients underwent surgical gastrostomies for enteral nutrition. The Stamm technique was employed in all cases. Men constituted 76 (88%) of the cases and the mean age was 58.4 years, the maximum age being 87 years and the minimum 19. We observed 16 (18.60%) minor complications, 17 (19.76%) serious complications and 8 (9.3%) perioperative deaths. CONCLUSION: Surgical gastrostomy, while considered a smaller procedure, is not without complications and mortality. The Stamm technique, despite the complications reported, is easy to perform and to handle, as well as safe.OBJETIVO: revizar as indicações e as complicações observadas após a realização de gastrostomias cirúrgicas em pacientes internados em um hospital universitário público de ensino. MÉTODOS:estudo retrospectivo não randomizado de revisão dos prontuários médicos dos pacientes submetidos à gastrostomia cirúrgica nos últimos cinco anos, sobre as indicações e complicações. RESULTADOS: no período de 2007 a 2011, 86 pacientes foram submetidos à gastrostomias cirúrgicas para nutrição enteral. A técnica operatória utilizada foi a de Stamm na totalidade dos casos. Os homens constituíram 76 (88%) dos casos e a média de idade foi 58,4 anos, a idade máxima 87 anos e a mínima de 19 anos. Foram observadas 16 (18,60%) complicações consideradas menores, 17 (19,76%) complicações graves e oito (9,3%) óbitos peri-operatórios. CONCLUSÃO: as gastrostomias cirúrgicas, embora consideradas procedimentos de menor porte, não são isentas de complicações e mortalidade. A técnica operatória de Stamm, apesar das complicações relatadas, é de fácil execução, manuseio e oferece segurança.45846
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