106 research outputs found
Tests of the Las Campanas Distant Cluster Survey from Confirmation Observations for the ESO Distant Cluster Survey
The ESO Distant Cluster Survey (EDisCS) is a photometric and spectroscopic
study of the galaxy cluster population at two epochs, z~0.5 and z~0.8, drawn
from the Las Campanas Distant Cluster Survey (LCDCS). We report results from
the initial candidate confirmation stage of the program and use these results
to probe the properties of the LCDCS. Of the 30 candidates targeted, we find
statistically significant overdensities of red galaxies near 28. Of the ten
additional candidates serendipitously observed within the fields of the
targeted 30, we detect red galaxy overdensities near six. We test the
robustness of the published LCDCS estimated redshifts to misidentification of
the brighest cluster galaxy (BCG) in the survey data, and measure the spatial
alignment of the published cluster coordinates, the peak red galaxy
overdensity, and the brightest cluster galaxy. We conclude that for LCDCS
clusters out to z~0.8, 1) the LCDCS coordinates agree with the centroid of the
red galaxy overdensity to within 25'' (~150 h^{-1} kpc) for 34 out of 37
candidates with 3\sigma galaxy overdensities, 2) BCGs are typically coincident
with the centroid of the red galaxy population to within a projected separation
of 200 h^{-1} kpc (32 out of 34 confirmed candidates), 3) the red galaxy
population is strongly concentrated, and 4) the misidentification of the BCG in
the LCDCS causes a redshift error >0.1 in 15-20% of the LCDCS candidates. These
findings together help explain the success of the surface brightness
fluctuations detection method.Comment: 10 pages, 9 figures, accepted for publication in the November 10
issue of Ap
The Las Campanas Distant Cluster Survey - The Catalog
We present an optically-selected catalog of 1073 galaxy cluster and group
candidates at 0.3<z<1. These candidates are drawn from the Las Campanas Distant
Clusters Survey (LCDCS), a drift-scan imaging survey of a 130 square degree
strip of the southern sky. To construct this catalog we utilize a novel
detection process in which clusters are detected as positive surface brightness
fluctuations in the background sky. This approach permits us to find clusters
with significantly shallower data than other matched-filter methods that are
based upon number counts of resolved galaxies. Selection criteria for the
survey are fully automated so that this sample constitutes a well-defined,
homogeneous sample that can be used to address issues of cluster evolution and
cosmology. Estimated redshifts are derived for the entire sample, and an
observed correlation between surface brightness and velocity dispersion (sigma)
is used to estimate the limiting velocity dispersion of the survey as a
function of redshift. We find a net surface density of 15.5 candidates per
square degree at z_{est}>0.3, with a false-detection rate of 30%. At z=0.3 we
probe down to the level of poor groups while by z=0.8 we detect only the most
massive systems (sigma>1000 km/s). We also present a supplemental catalog of
112 candidates that fail one or more of the automated selection criteria, but
appear from visual inspection to be bona fide clusters.Comment: 44 pages including 22 figures. Accepted to ApJS. Minor change in
section
The evolution of the density of galaxy clusters and groups: denser environments at higher redshifts
We show that, observationally, the projected local density distribution in
high-z clusters is shifted towards higher values compared to clusters at lower
redshift. To search for the origin of this evolution, we analyze a sample of
haloes selected from the Millennium Simulation and populated using
semi-analytic models, investigating the relation between observed projected
density and physical 3D density, using densities computed from the 10 and 3
closest neighbours. Both observationally and in the simulations, we study the
relation between number of cluster members and cluster mass, and number of
members per unit of cluster mass. We find that the observed evolution of
projected densities reflects a shift to higher values of the physical 3D
density distribution. In turn, this must be related with the globally higher
number of galaxies per unit of cluster volume N/V in the past. We show that the
evolution of N/V is due to a combination of two effects: a) distant clusters
were denser in dark matter (DM) simply because the DM density within R_{200}
(~the cluster virial radius) is defined to be a fixed multiple of the critical
density of the Universe, and b) the number of galaxies per unit of cluster DM
mass is remarkably constant both with redshift and cluster mass if counting
galaxies brighter than a passively evolving magnitude limit. Our results
highlight that distant clusters were much denser environments than today's
clusters, both in galaxy number and mass, and that the density conditions felt
by galaxies in virialized systems do not depend on the system mass.Comment: accepted for publication in MNRA
Cl 1103.7-1245 at z=0.96: the highest redshift galaxy cluster in the EDisCS survey
We present new spectroscopic observations in a field containing the highest
redshift cluster of the ESO Distant Cluster Survey (EDisCS). We measure galaxy
redshifts and determine the velocity dispersions of the galaxy structures
located in this field. Together with the main cluster Cl1103.71245
(z=0.9580; sigma_{clus} = 522 +/- 111 km/s) we find a secondary structure at
z=0.9830, Cl1103.7-1245c. We then characterize the galaxy properties in both
systems, and find that they contain very different galaxy populations. The
cluster Cl1103.7-1245 hosts a mixture of passive elliptical galaxies and
star-forming spirals and irregulars. In the secondary structure Cl1103.7-1245c
all galaxies are lower-mass star-forming irregulars and peculiars. In addition,
we compare the galaxy populations in the Cl1103.7-1245 z=0.9580 cluster with
those in lower redshift EDisCS clusters with similar velocity dispersions. We
find that the properties of the galaxies in Cl1103.7-1245 follow the
evolutionary trends found at lower redshifts: the number of cluster members
increases with time in line with the expected growth in cluster mass, and the
fraction of passive early-type galaxies increases with time while star-forming
late types become less dominant. Finally, we find that the mean stellar masses
are similar in all clusters, suggesting that massive cluster galaxies were
already present at z~1.Comment: A&A in pres
How special are Brightest Group and Cluster Galaxies?
We use the Sloan Digital Sky Survey to construct a sample of 625 brightest
group and cluster galaxies (BCGs) together with control samples of non-BCGs
matched in stellar mass, redshift, and color. We investigate how the systematic
properties of BCGs depend on stellar mass and on their privileged location near
the cluster center. The groups and clusters that we study are drawn from the C4
catalogue of Miller et al. (2005) but we have developed improved algorithms for
identifying the BCG and for measuring the cluster velocity dispersion. Since
the SDSS photometric pipeline tends to underestimate the luminosities of large
galaxies in dense environments, we have developed a correction for this effect
which can be readily applied to the published catalog data. We find that BCGs
are larger and have higher velocity dispersions than non-BCGs of the same
stellar mass, which implies that BCGs contain a larger fraction of dark matter.
In contrast to non-BCGs, the dynamical mass-to-light ratio of BCGs does not
vary as a function of galaxy luminosity. Hence BCGs lie on a different
fundamental plane than ordinary elliptical galaxies. BCGs also follow a steeper
Faber-Jackson relation than non-BCGs, as suggested by models in which BCGs
assemble via dissipationless mergers along preferentially radial orbits. We
find tentative evidence that this steepening is stronger in more massive
clusters. BCGs have similar mean stellar ages and metallicities to non-BCGs of
the same mass, but they have somewhat higher alpha/Fe ratios, indicating that
star formation may have occurred over a shorter timescale in the BCGs. Finally,
we find that BCGs are more likely to host radio-loud active galactic nuclei
than other galaxies of the same mass, but are less likely to host an optical
AGN. The differences we find are more pronounced for the less massive BCGs.Comment: Replaced with slightly modified version accepted by MNRAS. 28 pages,
25 figures. Version with full resolution figures available at
http://www.mpa-garching.mpg.de/~anja/bcgs_avdl.pd
The ROSAT International X-ray/Optical Survey (RIXOS): source catalogue
We describe the ROSAT International X-ray/Optical Survey (RIXOS), a medium-sensitivity survey and optical identification of X-ray sources discovered in ROSAT high Galactic latitude fields (|b|>28°) and observed with the Position Sensitive Proportional Counter (PSPC) detector. The survey made use of the central 17 arcmin of each ROSAT field. A flux limit of 3Ă10â14 erg cmâ2 sâ1 (0.5â2 keV) was adopted for the survey, and a minimum exposure time of 8000 s was required for qualifying ROSAT observations. X-ray sources in the survey are therefore substantially above the detection threshold of each field used, and many contain enough counts to allow the X-ray spectral slope to be estimated.
Spectroscopic observations of potential counterparts were obtained of all sources down to the survey limit in 64 fields, totalling a sky area of 15.77 deg2. Positive optical identifications are made for 94 per cent of the 296 sources thus examined. A further 18 fields (4.44 deg2), containing 105 sources above the 3Ă10â14 erg cmâ2 sâ1 survey limit, are completely optically identified to a higher flux of 8Ă10â14 erg cmâ2 sâ1 (0.5â2 keV). Optical spectroscopic data are supplemented by deep CCD imaging of many sources to reveal the morphology of the optical counterparts, and objects too faint to register on Sky Survey plates. The faintest optical counterparts have RâŒ22.
This paper describes the survey method, and presents a catalogue of the RIXOS sources and their optical identifications. Finding charts based on Sky Survey data are given for each source, supplemented by CCD imaging where necessary
Diffuse stellar emission in X-ray luminous galaxy clusters at z~0.3 I. Is the diffuse optical light boosted and rejuvenated in merging clusters?
[Abridged] We searched for diffuse stellar emission around BCGs in three of
the most X-ray luminous clusters found at z~0.3 in the REFLEX cluster survey
and observed with XMM-Newton. These systems (RXCJ0014.3-3022, RXCJ0232.2-4420,
and RXCJ2308.3-0211) are in different dynamical states, as witnessed by their
X-ray morphology and optical appearence (e.g. multiplicity of BCGs). [Abridged]
Diffuse stellar emission is robustly detected down to a surface brightness of
26 R-mag/arcsec^2 (observed frame) around a total of seven BCGs, extending up
to galactocentric distances of ~100 kpc. In particular, it surrounds a pair of
BCGs in RXCJ0232.2-4420, while it bridges two BCGs associated with the minor
subcomponent of the merging cluster RXCJ0014.3-3022. The diffuse light detected
at the greatest distances from the BCGs of the rather regular clusters
RXCJ0232.2-4420 and RXCJ2308.3-0211 follows the ICM distribution. Its B-R
colour is consistent with the colours measured within the BCG effective radii.
The diffuse light around the two pairs of BCGs in RXCJ0014.3-3022 exhibits
bluer colours than the BCG central regions by up to 0.5 mag. If the
contribution of the intracluster light (ICL) to the detected diffuse light
around BCGs is not negligible, ICL and BCGs have similar stellar populations in
relatively relaxed clusters. Merging on a cluster scale eventually adds
gravitational stresses to BCGs and other galaxies in subcluster cores. This
event may affect the properties of the diffuse stellar emission around BCGs.
Shredding of star-forming, low-metallicity dwarf galaxies is favoured as the
cause of the bluer B-R colours of the diffuse stellar component around the two
pairs of BCGs in the merging cluster RXCJ0014.3-3022.Comment: 20 pages including 3 tables and 11 low-resolution colour figures,
accepted for publication in A&
Decline in Kidney Function among Apparently Healthy Young Adults at Risk of Mesoamerican Nephropathy
Background Epidemic levels of CKD of undetermined cause, termed Mesoamerican nephropathy in Central America, have been found in low- and middle-income countries. We investigated the natural history of, and factors associated with, loss of kidney function in a population at high risk for this disease.Methods We conducted a 2-year prospective, longitudinal study with follow-up every 6 months in nine rural communities in northwestern Nicaragua and included all men (n=263) and a random sample of women (n=87) ages 18-30 years old without self-reported CKD, diabetes, or hypertension. We used growth mixture modeling to identify subgroups of eGFR trajectory and weighted multinomial logistic regression to examine associations with proposed risk factors.Results Among men, we identified three subpopulations of eGFR trajectory (mean baseline eGFR; mean eGFR change over follow-up): 81% remained stable (116 ml/min per 1.73 m2; -0.6 ml/min per 1.73 m2 per year), 9.5% experienced rapid decline despite normal baseline function (112 ml/min per 1.73 m2; -18.2 ml/min per 1.73 m2 per year), and 9.5% had baseline dysfunction (58 ml/min per 1.73 m2; -3.8 ml/min per 1.73 m2 per year). Among women: 96.6% remained stable (121 ml/min per 1.73 m2; -0.6 ml/min per 1.73 m2 per year), and 3.4% experienced rapid decline (132 ml/min per 1.73 m2; -14.6 ml/min per 1.73 m2 per year; n=3 women). Among men, outdoor and agricultural work and lack of shade availability during work breaks, reported at baseline, were associated with rapid decline.Conclusions Although Mesoamerican nephropathy is associated with agricultural work, other factors may also contribute to this disease
Metabolomic Profiling of Drug Responses in Acute Myeloid Leukaemia Cell Lines
Combined bezafibrate (BEZ) and medroxyprogesterone acetate (MPA) exert unexpected antileukaemic activities against acute myeloid leukaemia (AML) and these activities are associated with the generation of reactive oxygen species (ROS) within the tumor cells. Although the generation of ROS by these drugs is supported by preceding studies including our own, the interrelationship between the cellular effects of the drugs and ROS generation is not well understood. Here we report the use of NMR metabolomic profiling to further study the effect of BEZ and MPA on three AML cell lines and to shed light on the underlying mechanism of action. For this we focused on drug effects induced during the initial 24 hours of treatment prior to the onset of overt cellular responses and examined these in the context of basal differences in metabolic profiles between the cell lines. Despite their ultimately profound cellular effects, the early changes in metabolic profiles engendered by these drugs were less pronounced than the constitutive metabolic differences between cell types. Nonetheless, drug treatments engendered common metabolic changes, most markedly in the response to the combination of BEZ and MPA. These responses included changes to TCA cycle intermediates consistent with recently identified chemical actions of ROS. Notable amongst these was the conversion of α-ketoglutarate to succinate which was recapitulated by the treatment of cell extracts with exogenous hydrogen peroxide. These findings indicate that the actions of combined BEZ and MPA against AML cells are indeed mediated downstream of the generation of ROS rather than some hitherto unsuspected mechanism. Moreover, our findings demonstrate that metabolite profiles represent highly sensitive markers for genomic differences between cells and their responses to external stimuli. This opens new perspectives to use metabolic profiling as a tool to study the rational redeployment of drugs in new disease settings
The Fourteenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the extended Baryon Oscillation Spectroscopic Survey and from the second phase of the Apache Point Observatory Galactic Evolution Experiment
The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) has been in
operation since July 2014. This paper describes the second data release from
this phase, and the fourteenth from SDSS overall (making this, Data Release
Fourteen or DR14). This release makes public data taken by SDSS-IV in its first
two years of operation (July 2014-2016). Like all previous SDSS releases, DR14
is cumulative, including the most recent reductions and calibrations of all
data taken by SDSS since the first phase began operations in 2000. New in DR14
is the first public release of data from the extended Baryon Oscillation
Spectroscopic Survey (eBOSS); the first data from the second phase of the
Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE-2),
including stellar parameter estimates from an innovative data driven machine
learning algorithm known as "The Cannon"; and almost twice as many data cubes
from the Mapping Nearby Galaxies at APO (MaNGA) survey as were in the previous
release (N = 2812 in total). This paper describes the location and format of
the publicly available data from SDSS-IV surveys. We provide references to the
important technical papers describing how these data have been taken (both
targeting and observation details) and processed for scientific use. The SDSS
website (www.sdss.org) has been updated for this release, and provides links to
data downloads, as well as tutorials and examples of data use. SDSS-IV is
planning to continue to collect astronomical data until 2020, and will be
followed by SDSS-V.Comment: SDSS-IV collaboration alphabetical author data release paper. DR14
happened on 31st July 2017. 19 pages, 5 figures. Accepted by ApJS on 28th Nov
2017 (this is the "post-print" and "post-proofs" version; minor corrections
only from v1, and most of errors found in proofs corrected
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