210 research outputs found
Land subsidence susceptibility mapping in South Korea using machine learning algorithms
© 2018 by the authors. Licensee MDPI, Basel, Switzerland. In this study, land subsidence susceptibility was assessed for a study area in South Korea by using four machine learning models including Bayesian Logistic Regression (BLR), Support Vector Machine (SVM), Logistic Model Tree (LMT) and Alternate Decision Tree (ADTree). Eight conditioning factors were distinguished as the most important affecting factors on land subsidence of Jeong-am area, including slope angle, distance to drift, drift density, geology, distance to lineament, lineament density, land use and rock-mass rating (RMR) were applied to modelling. About 24 previously occurred land subsidence were surveyed and used as training dataset (70% of data) and validation dataset (30% of data) in the modelling process. Each studied model generated a land subsidence susceptibility map (LSSM). The maps were verified using several appropriate tools including statistical indices, the area under the receiver operating characteristic (AUROC) and success rate (SR) and prediction rate (PR) curves. The results of this study indicated that the BLR model produced LSSM with higher acceptable accuracy and reliability compared to the other applied models, even though the other models also had reasonable results
The growth and assembly of a massive galaxy at z ~ 2
We study the stellar mass assembly of the Spiderweb Galaxy (MRC 1138-262), a
massive z = 2.2 radio galaxy in a protocluster and the probable progenitor of a
brightest cluster galaxy. Nearby protocluster galaxies are identified and their
properties are determined by fitting stellar population models to their
rest-frame ultraviolet to optical spectral energy distributions. We find that
within 150 kpc of the radio galaxy the stellar mass is centrally concentrated
in the radio galaxy, yet most of the dust-uncorrected, instantaneous star
formation occurs in the surrounding low-mass satellite galaxies. We predict
that most of the galaxies within 150 kpc of the radio galaxy will merge with
the central radio galaxy by z = 0, increasing its stellar mass by up to a
factor of ~ 2. However, it will take several hundred Myr for the first mergers
to occur, by which time the large star formation rates are likely to have
exhausted the gas reservoirs in the satellite galaxies. The tidal radii of the
satellite galaxies are small, suggesting that stars and gas are being stripped
and deposited at distances of tens of kpc from the central radio galaxy. These
stripped stars may become intracluster stars or form an extended stellar halo
around the radio galaxy, such as those observed around cD galaxies in cluster
cores.Comment: 12 pages, accepted for publication in MNRA
On the phase-space structure of galaxy clusters from cosmological simulations
Cosmological N-body simulations represent an excellent tool to study the formation and evolution of dark matter (DM) haloes and the mechanisms that have originated the universal profile at the largest mass scales in the Universe. In particular, the combination of the velocity dispersion \u3c3v with the density p can be used to define the pseudo-entropy S(r) = \u3c32 v /p 2/3, whose profile is well described by a simple power law S 1e r \u3b1. We analyse a set of cosmological hydrodynamical re-simulations of massive galaxy clusters and study the pseudo-entropy profiles as traced by different collisionless components in simulated galaxy clusters: DM, stars, and substructures. We analyse four sets of simulations, exploring different resolution and physics (N-body and full hydrodynamical simulations) to investigate convergence and the impact of baryons. We find that baryons significantly affect the inner region of pseudo-entropy profiles as traced by substructures, while DM particles profiles are characterized by an almost universal behaviour, thus suggesting that the level of pseudo-entropy could represent a potential low-scatter mass-proxy. We compare observed and simulated pseudo-entropy profiles and find good agreement in both normalization and slope. We demonstrate, however, that the method used to derive observed pseudo-entropy profiles could introduce biases and underestimate the impact of mergers. Finally, we investigate the pseudo-entropy traced by the stars focusing our interest in the dynamical distinction between intracluster light and the stars bound to the brightest cluster galaxy: The combination of these two pseudo-entropy profiles is well described by a single power law out to almost the entire cluster virial radius
Optical followup of galaxy clusters detected by the South Pole Telescope
The South Pole Telescope (SPT) is a 10 meter telescope operating at mm
wavelengths. It has recently completed a three-band survey covering 2500 sq.
degrees. One of the survey's main goals is to detect galaxy clusters using
Sunyaev-Zeldovich effect and use these clusters for a variety of cosmological
and astrophysical studies such as the dark energy equation of state, the
primordial non-gaussianity and the evolution of galaxy populations. Since 2005,
we have been engaged in a comprehensive optical and near-infrared followup
program (at wavelengths between 0.4 and 5 {\mu}m) to image high-significance
SPT clusters, to measure their photometric redshifts, and to estimate the
contamination rate of the candidate lists. These clusters are then used for
various cosmological and astrophysical studies.Comment: For TAUP 2011 proceeding
South Pole Telescope Detections of the Previously Unconfirmed Planck Early SZ Clusters in the Southern Hemisphere
We present South Pole Telescope (SPT) observations of the five galaxy cluster
candidates in the southern hemisphere which were reported as unconfirmed in the
Planck Early Sunyaev-Zel'dovich (ESZ) sample. One cluster candidate, PLCKESZ
G255.62-46.16, is located in the 2500-square-degree SPT SZ survey region and
was reported previously as SPT-CL J0411-4819. For the remaining four
candidates, which are located outside of the SPT SZ survey region, we performed
short, dedicated SPT observations. Each of these four candidates was strongly
detected in maps made from these observations, with signal-to-noise ratios
ranging from 6.3 to 13.8. We have observed these four candidates on the
Magellan-Baade telescope and used these data to estimate cluster redshifts from
the red sequence. Resulting redshifts range from 0.24 to 0.46. We report
measurements of Y_0.75', the integrated Comptonization within a 0.75' radius,
for all five candidates. We also report X-ray luminosities calculated from
ROSAT All-Sky Survey catalog counts, as well as optical and improved SZ
coordinates for each candidate. The combination of SPT SZ measurements, optical
red-sequence measurements, and X-ray luminosity estimates demonstrates that
these five Planck ESZ cluster candidates do indeed correspond to real galaxy
clusters with redshifts and observable properties consistent with the rest of
the ESZ sample.Comment: 7 emulateapj pages, 4 figures, 1 table. Revised to match published
versio
The Redshift Evolution of the Mean Temperature, Pressure, and Entropy Profiles in 80 SPT-Selected Galaxy Clusters
(Abridged) We present the results of an X-ray analysis of 80 galaxy clusters
selected in the 2500 deg^2 South Pole Telescope survey and observed with the
Chandra X-ray Observatory. We divide the full sample into subsamples of ~20
clusters based on redshift and central density, performing an X-ray fit to all
clusters in a subsample simultaneously, assuming self-similarity of the
temperature profile. This approach allows us to constrain the shape of the
temperature profile over 0<r<1.5R500, which would be impossible on a
per-cluster basis, since the observations of individual clusters have, on
average, 2000 X-ray counts. The results presented here represent the first
constraints on the evolution of the average temperature profile from z=0 to
z=1.2. We find that high-z (0.6<z<1.2) clusters are slightly (~40%) cooler both
in the inner (rR500) regions than their low-z
(0.3<z<0.6) counterparts. Combining the average temperature profile with
measured gas density profiles from our earlier work, we infer the average
pressure and entropy profiles for each subsample. Overall, our observed
pressure profiles agree well with earlier lower-redshift measurements,
suggesting minimal redshift evolution in the pressure profile outside of the
core. We find no measurable redshift evolution in the entropy profile at
rR500 in
our high-z subsample. This flattening is consistent with a temperature bias due
to the enhanced (~3x) rate at which group-mass (~2 keV) halos, which would go
undetected at our survey depth, are accreting onto the cluster at z~1. This
work demonstrates a powerful method for inferring spatially-resolved cluster
properties in the case where individual cluster signal-to-noise is low, but the
number of observed clusters is high.Comment: 17 pages, 13 figures, submitted to ApJ. Updated following referee
repor
Mass Calibration and Cosmological Analysis of the SPT-SZ Galaxy Cluster Sample Using Velocity Dispersion and X-ray Measurements
We present a velocity dispersion-based mass calibration of the South Pole
Telescope Sunyaev-Zel'dovich effect survey (SPT-SZ) galaxy cluster sample.
Using a homogeneously selected sample of 100 cluster candidates from 720 deg2
of the survey along with 63 velocity dispersion () and 16 X-ray Yx
measurements of sample clusters, we simultaneously calibrate the
mass-observable relation and constrain cosmological parameters. The
calibrations using and Yx are consistent at the level,
with the calibration preferring ~16% higher masses. We use the full
cluster dataset to measure . The
SPT cluster abundance is lower than preferred by either the WMAP9 or
Planck+WMAP9 polarization (WP) data, but assuming the sum of the neutrino
masses is eV, we find the datasets to be consistent at the
1.0 level for WMAP9 and 1.5 for Planck+WP. Allowing for larger
further reconciles the results. When we combine the cluster and
Planck+WP datasets with BAO and SNIa, the preferred cluster masses are
higher than the Yx calibration and higher than the
calibration. Given the scale of these shifts (~44% and ~23% in mass,
respectively), we execute a goodness of fit test; it reveals no tension,
indicating that the best-fit model provides an adequate description of the
data. Using the multi-probe dataset, we measure and
. Within a CDM model we find eV. We present a consistency test of the cosmic growth rate.
Allowing both the growth index and the dark energy equation of state
parameter to vary, we find and ,
demonstrating that the expansion and the growth histories are consistent with a
LCDM model ().Comment: Accepted by ApJ (v2 is accepted version); 17 pages, 6 figure
SPT-CLJ2040-4451: An SZ-Selected Galaxy Cluster at z = 1.478 With Significant Ongoing Star Formation
SPT-CLJ2040-4451 -- spectroscopically confirmed at z = 1.478 -- is the
highest redshift galaxy cluster yet discovered via the Sunyaev-Zel'dovich
effect. SPT-CLJ2040-4451 was a candidate galaxy cluster identified in the first
720 deg^2 of the South Pole Telescope Sunyaev-Zel'dovich (SPT-SZ) survey, and
confirmed in follow-up imaging and spectroscopy. From multi-object spectroscopy
with Magellan-I/Baade+IMACS we measure spectroscopic redshifts for 15 cluster
member galaxies, all of which have strong [O II] 3727 emission.
SPT-CLJ2040-4451 has an SZ-measured mass of M_500,SZ = 3.2 +/- 0.8 X 10^14
M_Sun/h_70, corresponding to M_200,SZ = 5.8 +/- 1.4 X 10^14 M_Sun/h_70. The
velocity dispersion measured entirely from blue star forming members is sigma_v
= 1500 +/- 520 km/s. The prevalence of star forming cluster members (galaxies
with > 1.5 M_Sun/yr) implies that this massive, high-redshift cluster is
experiencing a phase of active star formation, and supports recent results
showing a marked increase in star formation occurring in galaxy clusters at z
>1.4. We also compute the probability of finding a cluster as rare as this in
the SPT-SZ survey to be >99%, indicating that its discovery is not in tension
with the concordance Lambda-CDM cosmological model.Comment: 14 pages, 8 figures, 4 tables, Accepted to Ap
SPT-CL J0205-5829: A z = 1.32 Evolved Massive Galaxy Cluster in the South Pole Telescope Sunyaev-Zel'dovich Effect Survey
The galaxy cluster SPT-CL J0205-5829 currently has the highest
spectroscopically-confirmed redshift, z=1.322, in the South Pole Telescope
Sunyaev-Zel'dovich (SPT-SZ) survey. XMM-Newton observations measure a
core-excluded temperature of Tx=8.7keV producing a mass estimate that is
consistent with the Sunyaev-Zel'dovich derived mass. The combined SZ and X-ray
mass estimate of M500=(4.9+/-0.8)e14 h_{70}^{-1} Msun makes it the most massive
known SZ-selected galaxy cluster at z>1.2 and the second most massive at z>1.
Using optical and infrared observations, we find that the brightest galaxies in
SPT-CL J0205-5829 are already well evolved by the time the universe was <5 Gyr
old, with stellar population ages >3 Gyr, and low rates of star formation
(<0.5Msun/yr). We find that, despite the high redshift and mass, the existence
of SPT-CL J0205-5829 is not surprising given a flat LambdaCDM cosmology with
Gaussian initial perturbations. The a priori chance of finding a cluster of
similar rarity (or rarer) in a survey the size of the 2500 deg^2 SPT-SZ survey
is 69%.Comment: 11 pages, 5 figures, submitted to Ap
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