359 research outputs found
A study of the remarkable galaxy system AM 546-324 (the core of Abell S0546)
We report first results of an investigation of the tidally disturbed galaxy
system AM\,546-324, whose two principal galaxies 2MFGC 04711 and AM\,0546-324
(NED02) were previously classified as interacting doubles. This system was
selected to study the interaction of ellipticals in a moderately dense
environment. We provide spectral characteristics of the system and present an
observational study of the interaction effects on the morphology, kinematics,
and stellar population of these galaxies. The study is based on long-slit
spectrophotometric data in the range of 4500-8000 obtained with
the Gemini Multi-Object Spetrograph at Gemini South (GMOS-S). We have used the
stellar population synthesis code STARLIGHT to investigate the star formation
history of these galaxies. The Gemini/GMOS-S direct r-G0303 broad band pointing
image was used to enhance and study fine morphological structures. The main
absorption lines in the spectra were used to determine the radial velocity.
Along the whole long-slit signal, the spectra of the Shadowy galaxy (discovered
by us), 2MFGC 04711, and AM\,0546-324 (NED02) resemble that of an early-type
galaxy. We estimated redshifts of z= 0.0696, z= 0.0693 and z= 0.0718,
corresponding to heliocentric velocities of 20\,141 km s, 20\,057 km
s, and 20\,754 km s for the Shadowy galaxy, 2MFGC 04711 and
AM\,0546-324 (NED02), respectively. ..
The early-type dwarf galaxy population of the Centaurus cluster
We present a photometric study of the early-type dwarf galaxy population of
the Centaurus cluster, aiming at investigating the galaxy luminosity function
(LF) and galaxy scaling relations down to the regime of galaxies with M_V~-10
mag. On deep VLT/FORS1 V- and I-band images of the central part of the cluster,
we identify cluster dwarf-galaxy candidates using both morphological and
surface brightness selection criteria. Photometric and structural parameters of
the candidates are derived from analysis of their surface brightness profiles.
Fundamental scaling relations, such as the colour-magnitude and the
magnitude-surface brightness relation, are used to distinguish the cluster from
the background. We find a flat LF with a slope of \alpha = -1.14 \pm 0.12 for
M_V>-14 mag, when fitting a power law to the completeness-corrected galaxy
number counts. When plotting the central surface brightness of a Sersic model
vs. the galaxy magnitude, we find a continuous relation for magnitudes
-20<M_V<-10 mag, with only the brightest core galaxies deviating from this
relation, in agreement with previous studies of other clusters. In a
size-luminosity diagram of early-type galaxies from a range of environments, we
observe that R_eff slowly decreases with decreasing luminosity for -21<M_V<-13
mag and decreases more rapidly at fainter magnitudes. This trend continues to
the ultra-faint Local Group dwarf galaxies (M_V~-4 mag). The continuous central
surface brightness vs. absolute magnitude relation and the smooth relation in
the size-luminosity diagram over a wide range of magnitudes are consistent with
the interpretation of dwarf galaxies and more massive elliptical galaxies being
one family of objects with gradually changing structural properties. The most
massive core galaxies and the rare cE galaxies are the only exceptions.Comment: 14 pages, 10 figures, 4 tables, accepted for publication in A&
The architecture of Abell 1386 and its relationship to the Sloan Great Wall
We present new radial velocities from AAOmega on the Anglo-Australian
Telescope for 307 galaxies (b_J < 19.5) in the region of the rich cluster Abell
1386. Consistent with other studies of galaxy clusters that constitute
sub-units of superstructures, we find that the velocity distribution of A1386
is very broad (21,000--42,000 kms^-1, or z=0.08--0.14) and complex. The mean
redshift of the cluster that Abell designated as number 1386 is found to be
~0.104. However, we find that it consists of various superpositions of
line-of-sight components. We investigate the reality of each component by
testing for substructure and searching for giant elliptical galaxies in each
and show that A1386 is made up of at least four significant clusters or groups
along the line of sight whose global parameters we detail. Peculiar velocities
of brightest galaxies for each of the groups are computed and found to be
different from previous works, largely due to the complexity of the sky area
and the depth of analysis performed in the present work. We also analyse A1386
in the context of its parent superclusters: Leo A, and especially the Sloan
Great Wall. Although the new clusters may be moving toward mass concentrations
in the Sloan Great Wall or beyond, many are most likely not yet physically
bound to it.Comment: 21 pages, 9 figures, includes the full appendix table. Accepted for
publication in MNRA
Does hypoglycemia following a glucose challenge test identify a high risk pregnancy?
<p>Abstract</p> <p>Objective</p> <p>An association between maternal hypoglycemia during pregnancy with fetal growth restriction and overall perinatal mortality has been reported. In a retrospective pilot study we found that hypoglycemia was linked with a greater number of special care/neonatal intensive care unit admissions and approached significance in the number of women who developed preeclampsia. That study was limited by its retrospective design, a narrow patient population and the inability to perform multivariate analysis because of the limitations in the data points collected. This study was undertaken to compare the perinatal outcome in pregnancies with hyoglycemia following a glucose challenge test (GCT) to pregnancies with a normal GCT.</p> <p>Methods</p> <p>Obstetric patients (not pre-gestational diabetics or gestational diabetes before 24 weeks were eligible. Women with a 1 hour glucose ≤ 88 mg/dL (4.8 m/mol) following a 50-gram oral GCT were matched with the next patient with a 1 hour glucose of 89–139 mg/dL. Pregnancy outcomes were evaluated.</p> <p>Results</p> <p>Over 22 months, 436 hypoglycemic patients and 434 normal subjects were identified. Hypoglycemia was increased in women < 25 (p = 0.003) and with pre-existing medical conditions (p < 0.001). Hypoglycemia was decreased if pre-pregnancy BMI ≥ 30 (p = 0.008).</p> <p>Preeclampsia/eclampsia was more common in hypoglycemic women. (OR = 3.13, 95% CI 1.51 – 6.51, p = 0.002) but not other intrapartum and perinatal outcomes.</p> <p>Conclusion</p> <p>Hypoglycemic patients are younger, have reduced pre-pregnancy weight, lower BMIs, and are more likely to develop preeclampsia than normoglycemic women.</p
Cross Correlations of X-ray and Optically Selected Clusters With Near Infrared and Optical Galaxies
We compute the real-space cluster-galaxy cross-correlation xi_cg(r) using the
ROSAT-ESO Flux Limited X-ray (REFLEX) cluster survey, a group catalogue
constructed from the final version of the 2dFGRS, and galaxies extracted from
2MASS and APM surveys. This first detailed calculation of the cross-correlation
for X-ray clusters and groups, is consistent with previous works and shows that
xi_cg(r) can not be described by a single power law. We analyse the clustering
dependence on the cluster X-ray luminosity L_X and virial mass M_vir thresholds
as well as on the galaxy limiting magnitude. We also make a comparison of our
results with those obtained for the halo-mass cross-correlation function in a
LambdaCDM N-body simulation to infer the scale dependence of galaxy bias around
clusters. Our results indicate that the distribution of galaxies shows a
significant anti-bias at highly non-linear small cluster-centric distances
(b_cg(r) ~ 0.7), irrespective of the group/cluster virial mass or X-ray
luminosity and galaxy characteristics, which show that a generic process
controls the efficiency of galaxy formation and evolution in high density
regions. On larger scales b_cg(r) rises to a nearly constant value of order
unity, the transition occuring at approximately 2 Mpch^(-1) for 2dF groups and
5 Mpch^(-1) for REFLEX clusters.Comment: 9 pages, 6 figures. Minor changes, replaced to match version accepted
for publication in MNRA
Orientation bias of optically selected galaxy clusters and its impact on stacked weak-lensing analyses
Weak-lensing measurements of the averaged shear profiles of galaxy clusters binned by some proxy for cluster mass are commonly converted to cluster mass estimates under the assumption that these cluster stacks have spherical symmetry. In this paper, we test whether this assumption holds for optically selected clusters binned by estimated optical richness. Using mock catalogues created from N-body simulations populated realistically with galaxies, we ran a suite of optical cluster finders and estimated their optical richness. We binned galaxy clusters by true cluster mass and estimated optical richness and measure the ellipticity of these stacks. We find that the processes of optical cluster selection and richness estimation are biased, leading to stacked structures that are elongated along the line of sight. We show that weak-lensing alone cannot measure the size of this orientation bias. Weak-lensing masses of stacked optically selected clusters are overestimated by up to 3–6 per cent when clusters can be uniquely associated with haloes. This effect is large enough to lead to significant biases in the cosmological parameters derived from large surveys like the Dark Energy Survey, if not calibrated via simulations or fitted simultaneously. This bias probably also contributes to the observed discrepancy between the observed and predicted Sunyaev–Zel’dovich signal of optically selected clusters
Prioritization of fish communities with a view to conservation and restoration on a large scale European basin, the Loire (France)
The hierarchical organization of important sites for the conservation or the
restoration of fish communities is a great challenge for managers, especially because of
financial or time constraints. In this perspective, we developed a methodology, which is
easy to implement in different locations. Based on the fish assemblage characteristics of
the Loire basin (France), we created a synthetic conservation value index including the
rarity, the conservation status and the species origin. The relationship between this new
synthetic index and the Fish-Based Index allowed us to establish a classification protocol
of the sites along the Loire including fish assemblages to be restored or conserved. Sites
presenting disturbed fish assemblages, a low rarity index, few threatened species, and a
high proportion of non-native species were considered as important for the restoration of
fish biodiversity. These sites were found mainly in areas where the assemblages are
typical of the bream zone, e.g. with a higher number of eurytopic and limnophilic
species. On the contrary, important sites for conservation were defined as having an
important conservation potential (high RI, a lot of threatened species, and few nonnatives
fish species) and an undisturbed fish assemblage similar to the expected community
if habitats are undisturbed. Important sites for conservation were found in the
Loire basin’s medium reaches which host assemblages typical for the grayling and the
barbell zones, e.g. with a higher number of rheophilic species. The synthetic conservation value index could be adapted and completed with other criteria according to
management priorities and capacities
Scale-invariance of galaxy clustering
Some years ago we proposed a new approach to the analysis of galaxy and
cluster correlations based on the concepts and methods of modern statistical
Physics. This led to the surprising result that galaxy correlations are fractal
and not homogeneous up to the limits of the available catalogs. The usual
statistical methods, which are based on the assumption of homogeneity, are
therefore inconsistent for all the length scales probed so far, and a new, more
general, conceptual framework is necessary to identifythe real physical
properties of these structures. In the last few years the 3-d catalogs have
been significatively improved and we have extended our methods to the analysis
of number counts and angular catalogs. This has led to a complete analysis of
all the available data that we present in this review. The result is that
galaxy structures are highly irregular and self-similar: all the available data
are consistent with each other and show fractal correlations (with dimension ) up to the deepest scales probed so far (1000 \hmp) and even more
as indicated from the new interpretation of the number counts. The evidence for
scale-invariance of galaxy clustering is very strong up to 150 \hmp due to
the statistical robustness of the data but becomes progressively weaker
(statistically) at larger distances due to the limited data. In These facts
lead to fascinating conceptual implications about our knowledge of the universe
and to a new scenario for the theoretical challenge in this field.Comment: Latex file 165 pages, 106 postscript figures. This paper is also
available at http://www.phys.uniroma1.it/DOCS/PIL/pil.html To appear in
Physics Report (Dec. 1997
Restricted-Range Fishes and the Conservation of Brazilian Freshwaters
Background: Freshwaters are the most threatened ecosystems on earth. Although recent assessments provide data on global priority regions for freshwater conservation, local scale priorities remain unknown. Refining the scale of global biodiversity assessments (both at terrestrial and freshwater realms) and translating these into conservation priorities on the ground remains a major challenge to biodiversity science, and depends directly on species occurrence data of high taxonomic and geographic resolution. Brazil harbors the richest freshwater ichthyofauna in the world, but knowledge on endemic areas and conservation in Brazilian rivers is still scarce. Methodology/Principal Findings: Using data on environmental threats and revised species distribution data we detect and delineate 540 small watershed areas harboring 819 restricted-range fishes in Brazil. Many of these areas are already highly threatened, as 159 (29%) watersheds have lost more than 70% of their original vegetation cover, and only 141 (26%) show significant overlap with formally protected areas or indigenous lands. We detected 220 (40%) critical watersheds overlapping hydroelectric dams or showing both poor formal protection and widespread habitat loss; these sites harbor 344 endemic fish species that may face extinction if no conservation action is in place in the near future. Conclusions/Significance: We provide the first analysis of site-scale conservation priorities in the richest freshwater ecosystems of the globe. Our results corroborate the hypothesis that freshwater biodiversity has been neglected in former conservation assessments. The study provides a simple and straightforward method for detecting freshwater priority areas based on endemism and threat, and represents a starting point for integrating freshwater and terrestrial conservation in representative and biogeographically consistent site-scale conservation strategies, that may be scaled-up following naturally linked drainage systems. Proper management (e. g. forestry code enforcement, landscape planning) and conservation (e. g. formal protection) of the 540 watersheds detected herein will be decisive in avoiding species extinction in the richest aquatic ecosystems on the planet.Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES)Gordon and Betty Moore Foundatio
Nature and Environment of Very Luminous Galaxies
The most luminous galaxies in the blue passband have a larger correlation
amplitude than L* galaxies. They do not appear to be preferentially located in
rich clusters or groups, but a significant fraction of them seem to be in
systems which include fainter members.We present an analysis of fields centered
on 18 Very Luminous Galaxies (MB < -21) selected from the Southern Sky Redshift
Survey 2, based on new observations and public data of the 2dF Galaxy Redshift
Survey; we present also additional data on a CfA VLG and on Arp 127. We find
that all the selected VLGs are physically associated to fainter companions.
Moreover, there is a relation between the VLG morphology (early or late) and
the dynamical properties of the system, which reflects the morphology-density
relation. 6 out of the 18 SSRS2 VLGs are early type galaxies: 2 are in the
center of rich Abell clusters with velocity dispersion sigma ~600 km/s, and the
other 4 are in poor clusters or groups with sigma ~300. The VLG extracted from
the CfA catalog is also an elliptical in a Zwicky cluster. The remaining 2/3 of
the sample are late-type VLGs, generally found in poorer systems with a larger
spread in velocity dispersion, from ~100 up to ~750 km/s. The low velocity
dispersion, late-type VLG dominated systems appear to be the analogous of our
own Local Group. The possibile association of VLG systems to dark matter halos
with mass comparable to rich groups or clusters, as suggested by the comparable
correlation amplitude, would imply significant differences in the galaxy
formation process. This work also shows that observing fields around VLGs
represents an effective way of identifying galaxy systems which are not
selected through other traditional techniques.Comment: 21 pages, A&A, in pres
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