170 research outputs found
The GEEC2 spectroscopic survey of Galaxy Groups at
We present the data release of the Gemini-South GMOS spectroscopy in the
fields of 11 galaxy groups at , within the COSMOS field. This forms
the basis of the Galaxy Environment Evolution Collaboration 2 (GEEC2) project
to study galaxy evolution in haloes with across cosmic
time. The final sample includes spectroscopically--confirmed members with
per cent complete for galaxies within the virial
radius, and with stellar mass . Including
galaxies with photometric redshifts we have an effective sample size of galaxies within the virial radii of these groups. We present group
velocity dispersions, dynamical and stellar masses. Combining with the GCLASS
sample of more massive clusters at the same redshift we find the total stellar
mass is strongly correlated with the dynamical mass, with
. This stellar
fraction of per cent is lower than predicted by some halo occupation
distribution models, though the weak dependence on halo mass is in good
agreement. Most groups have an easily identifiable most massive galaxy (MMG)
near the centre of the galaxy distribution, and we present the spectroscopic
properties and surface brightness fits to these galaxies. The total stellar
mass distribution in the groups, excluding the MMG, compares well with an NFW
profile with concentration , for galaxies beyond . This is
more concentrated than the number density distribution, demonstrating that
there is some mass segregation.Comment: Accepted for publication in MNRAS. The appendix is omitted due to
large figures. The full version will be available from the MNRAS website and
from http://quixote.uwaterloo.ca/~mbalogh/papers/GEEC2_data.pdf. Long data
tables are available from MNRAS or by contacting the first autho
CAESAR source finder: recent developments and testing
A new era in radioastronomy will begin with the upcoming large-scale surveys
planned at the Australian Square Kilometre Array Pathfinder (ASKAP). ASKAP
started its Early Science program in October 2017 and several target fields
were observed during the array commissioning phase. The SCORPIO field was the
first observed in the Galactic Plane in Band 1 (792-1032 MHz) using 15
commissioned antennas. The achieved sensitivity and large field of view already
allow to discover new sources and survey thousands of existing ones with
improved precision with respect to previous surveys. Data analysis is currently
ongoing to deliver the first source catalogue. Given the increased scale of the
data, source extraction and characterization, even in this Early Science phase,
have to be carried out in a mostly automated way. This process presents
significant challenges due to the presence of extended objects and diffuse
emission close to the Galactic Plane. In this context we have extended and
optimized a novel source finding tool, named CAESAR , to allow extraction of
both compact and extended sources from radio maps. A number of developments
have been done driven by the analysis of the SCORPIO map and in view of the
future ASKAP Galactic Plane survey. The main goals are the improvement of
algorithm performances and scalability as well as of software maintainability
and usability within the radio community. In this paper we present the current
status of CAESAR and report a first systematic characterization of its
performance for both compact and extended sources using simulated maps. Future
prospects are discussed in light of the obtained results.Comment: 15 pages, 10 figure
A statistical analysis of the late-type stellar content in the Andromeda halo
We present a statistical characterization of the carbon-star to M-giant (C/M)
ratio in the halo of M31. Based on application of pseudo-filter band passes to
our Keck/DEIMOS spectra we measure the 81-77-color index of 1288 stars in the
giant stellar stream and in halo fields out to large distances. From this
well-established narrow-band system, supplemented by V-I colors, we find only a
low number (five in total) of C-star candidates. The resulting low C/M ratio of
10% is consistent with the values in the M31 disk and inner halo from the
literature. Although our analysis is challenged by small number statistics and
our sample selection, there is an indication that the oxygen-rich M-giants
occur in similar number throughout the entire halo. We also find no difference
in the C-star population of the halo fields compared to the giant stream. The
very low C/M ratio is at odds with the observed low metallicities and the
presence of intermediate-age stars at large radii. Our observed absence of a
substantial carbon star population in the these regions indicates that the
(outer) M31 halo cannot be dominated by the debris of disk-like or SMC-type
galaxies, but rather resemble the dwarf elliptical NGC 147.Comment: 11 pages, 10 figures, accepted for publication in the A
Extensive light profile fitting of galaxy-scale strong lenses
We investigate the merits of a massive forward modeling of ground-based
optical imaging as a diagnostic for the strong lensing nature of Early-Type
Galaxies, in the light of which blurred and faint Einstein rings can hide. We
simulate several thousand mock strong lenses under ground- and space-based
conditions as arising from the deflection of an exponential disk by a
foreground de Vaucouleurs light profile whose lensing potential is described by
a Singular Isothermal Ellipsoid. We then fit for the lensed light distribution
with sl_fit after having subtracted the foreground light emission off (ideal
case) and also after having fitted the deflector's light with galfit. By
setting thresholds in the output parameter space, we can decide the
lens/not-a-lens status of each system. We finally apply our strategy to a
sample of 517 lens candidates present in the CFHTLS data to test the
consistency of our selection approach. The efficiency of the fast modeling
method at recovering the main lens parameters like Einstein radius, total
magnification or total lensed flux, is quite comparable under CFHT and HST
conditions when the deflector is perfectly subtracted off (only possible in
simulations), fostering a sharp distinction between the good and the bad
candidates. Conversely, for a more realistic subtraction, a substantial
fraction of the lensed light is absorbed into the deflector's model, which
biases the subsequent fitting of the rings and then disturbs the selection
process. We quantify completeness and purity of the lens finding method in both
cases. This suggests that the main limitation currently resides in the
subtraction of the foreground light. Provided further enhancement of the
latter, the direct forward modeling of large numbers of galaxy-galaxy strong
lenses thus appears tractable and could constitute a competitive lens finder in
the next generation of wide-field imaging surveys.Comment: A&A accepted version, minor changes (13 pages, 10 figures
Weighing the Giants - I. Weak-lensing masses for 51 massive galaxy clusters: project overview, data analysis methods and cluster images
This is the first in a series of papers in which we measure accurate
weak-lensing masses for 51 of the most X-ray luminous galaxy clusters known at
redshifts 0.15<z<0.7, in order to calibrate X-ray and other mass proxies for
cosmological cluster experiments. The primary aim is to improve the absolute
mass calibration of cluster observables, currently the dominant systematic
uncertainty for cluster count experiments. Key elements of this work are the
rigorous quantification of systematic uncertainties, high-quality data
reduction and photometric calibration, and the "blind" nature of the analysis
to avoid confirmation bias. Our target clusters are drawn from RASS X-ray
catalogs, and provide a versatile calibration sample for many aspects of
cluster cosmology. We have acquired wide-field, high-quality imaging using the
Subaru and CFHT telescopes for all 51 clusters, in at least three bands per
cluster. For a subset of 27 clusters, we have data in at least five bands,
allowing accurate photo-z estimates of lensed galaxies. In this paper, we
describe the cluster sample and observations, and detail the processing of the
SuprimeCam data to yield high-quality images suitable for robust weak-lensing
shape measurements and precision photometry. For each cluster, we present
wide-field color optical images and maps of the weak-lensing mass distribution,
the optical light distribution, and the X-ray emission, providing insights into
the large-scale structure in which the clusters are embedded. We measure the
offsets between X-ray centroids and Brightest Cluster Galaxies in the clusters,
finding these to be small in general, with a median of 20kpc. For offsets
<100kpc, weak-lensing mass measurements centered on the BCGs agree well with
values determined relative to the X-ray centroids; miscentering is therefore
not a significant source of systematic uncertainty for our mass measurements.
[abridged]Comment: 26 pages, 19 figures (Appendix C not included). Accepted after minor
revisio
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Detection of melanoma skin cancer in dermoscopy images
Malignant melanoma is the most hazardous type of human skin cancer and its incidence has been rapidly increasing. Early detection of malignant melanoma in dermoscopy images is very important and critical, since its detection in the early stage can be helpful to cure it. Computer Aided Diagnosis systems can be very helpful to facilitate the early detection of cancers for dermatologists. In this paper, we present a novel method for the detection of melanoma skin cancer. To detect the hair and several noise from images, preprocessing step is carried out by applying a bank of directional lters. and therefore, Image inpainting method is implemented to ll in the unknown regions. Fuzzy C-Means and Markov Random Field methods are used to delineate the border of the lesion area in the images. The method was evaluated on a dataset of 200 dermoscopic images, and superior results were produced compared to alternative methods
CARS: the CFHTLS-Archive-Research Survey; I. Five-band multi-colour data from 37 sq. deg. CFHTLS-Wide observations
We present the CFHTLS-Archive-Research Survey (CARS). It is a virtual
multi-colour survey based on public archive images from the CFHT-Legacy-Survey.
Our main scientific interests in CARS are optical searches for galaxy clusters
from low to high redshift and their subsequent study with photometric and
weak-gravitational lensing techniques. As a first step of the project we
present multi-colour catalogues from 37 sq. degrees of the CFHTLS-Wide
component. Our aims are to create astrometrically and photometrically well
calibrated co-added images. Second goal are five-band (u*, g', r', i', z')
multi-band catalogues with an emphasis on reliable estimates for object
colours. These are subsequently used for photometric redshift estimates. The
article explains in detail data processing, multi-colour catalogue creation and
photometric redshift estimation. Furthermore we apply a novel technique, based
on studies of the angular galaxy cross-correlation function, to quantify the
reliability of photo-z's. The accuracy of our high-confidence photo-z sample
(10-15 galaxies per sq. arcmin) is estimated to up to i'<24 with typically only 1-3% outliers. Interested users can
obtain access to our data by request to the authors.Comment: 31 pages, 18 figures, 6 tables; accepted for publication by A&A main
journa
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H0LiCOW X: Spectroscopic/imaging survey and galaxy-group identification around the strong gravitational lens system WFI2033-4723
Galaxies and galaxy groups located along the line of sight towards
gravitationally lensed quasars produce high-order perturbations of the
gravitational potential at the lens position. When these perturbation are too
large, they can induce a systematic error on of a few-percent if the lens
system is used for cosmological inference and the perturbers are not explicitly
accounted for in the lens model. In this work, we present a detailed
characterization of the environment of the lens system WFI2033-4723 (, = 0.6575), one of the core targets of the H0LICOW
project for which we present cosmological inferences in a companion paper (Rusu
et al. 2019). We use the Gemini and ESO-Very Large telescopes to measure the
spectroscopic redshifts of the brightest galaxies towards the lens, and use the
ESO-MUSE integral field spectrograph to measure the velocity-dispersion of the
lens ( km/s) and of several nearby
galaxies. In addition, we measure photometric redshifts and stellar masses of
all galaxies down to mag, mainly based on Dark Energy Survey imaging
(DR1). Our new catalog, complemented with literature data, more than doubles
the number of known galaxy spectroscopic redshifts in the direct vicinity of
the lens, expanding to 116 (64) the number of spectroscopic redshifts for
galaxies separated by less than 3 arcmin (2 arcmin) from the lens. Using the
flexion-shift as a measure of the amplitude of the gravitational perturbation,
we identify 2 galaxy groups and 3 galaxies that require specific attention in
the lens models. The ESO MUSE data enable us to measure the
velocity-dispersions of three of these galaxies. These results are essential
for the cosmological inference analysis presented in Rusu et al. (2019).Comment: Matches the version accepted for publication by MNRAS. Note that this
paper previously appeared as H0LICOW X
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