15 research outputs found
Weak lensing density profiles and mass reconstructions of the galaxy clusters Abell 1351 and Abell 1995
The aim of the present work is to study the overall mass distribution of the
galaxy clusters Abell 1351 and Abell 1995 using weak gravitational lensing.
These clusters have got a very different mass structure and dynamical state,
and are the two extremes from a larger sample of 38 X-ray luminous clusters of
similar size and redshift.
We measure shear values of faint background galaxies and correct for PSF
anisotropies using the KSB+ method. Two-dimensional mass maps of the clusters
are created using a finite-field mass reconstruction algorithm, and verified
with aperture mass statistics. The masses inferred from the reconstructions are
compared to those obtained from fitting spherically symmetric SIS- and
NFW-models to the tangential shear profiles. We discuss the NFW concentration
parameters in detail.
From the mass reconstructions we infer M200-masses of 11.7 +/- 3.1 * 10^14
h_70^-1 Msun and 10.5 +/- 2.7 * 10^14 h_70^-1 Msun for Abell 1351 and Abell
1995, respectively. About 3' north-east of the main mass peak of Abell 1351 we
detect a significant secondary peak in the mass reconstruction as well as by
aperture mass statistics. This feature is also traced by clusters members
selected by means of their V-I colour, and hence is likely a real sub-structure
of Abell 1351. From our fits to the tangential shear we infer masses on the
order of M200 ~ 8-9 * 10^14 h_70^-1 Msun (Abell 1351) and M200 ~ 5-6 * 10^14
h_70^-1 Msun (Abell 1995). The concentration parameters remain poorly
constrained by our weak lensing analysis.Comment: 16 pages, 7 figures, Accepted for publication in A&
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
The afterglows of Swift-era gamma-ray bursts. I. Comparing pre-Swift and Swift-era long/soft (type II) GRB optical afterglows
We have gathered optical photometry data from the literature on a large sample of Swift-era gamma-ray burst (GRB) afterglows including GRBs up to 2009 September, for a total of 76 GRBs, and present an additional three pre-Swift GRBs not included in an earlier sample. Furthermore, we publish 840 additional new photometry data points on a total of 42 GRB afterglows, including large data sets for GRBs 050319, 050408, 050802, 050820A, 050922C, 060418, 080413A, and 080810. We analyzed the light curves of all GRBs in the sample and derived spectral energy distributions for the sample with the best data quality, allowing us to estimate the host-galaxy extinction. We transformed the afterglow light curves into an extinction-corrected z = 1 system and compared their luminosities with a sample of pre-Swift afterglows. The results of a former study, which showed that GRB afterglows clustered and exhibited a bimodal distribution in luminosity space, are weakened by the larger sample. We found that the luminosity distribution of the two afterglow samples (Swift-era and pre-Swift) is very similar, and that a subsample for which we were not able to estimate the extinction, which is fainter than the main sample, can be explained by assuming a moderate amount of line-of-sight host extinction. We derived bolometric isotropic energies for all GRBs in our sample, and found only a tentative correlation between the prompt energy release and the optical afterglow luminosity at 1 day after the GRB in the z = 1 system. A comparative study of the optical luminosities of GRB afterglows with echelle spectra (which show a high number of foreground absorbing systems) and those without, reveals no indication that the former are statistically significantly more luminous. Furthermore, we propose the existence of an upper ceiling on afterglow luminosities and study the luminosity distribution at early times, which was not accessible before the advent of the Swift satellite. Most GRBs feature afterglows that are dominated by the forward shock from early times on. Finally, we present the first indications of a class of long GRBs, which form a bridge between the typical highluminosity, high-redshift events and nearby low-luminosity events (which are also associated with spectroscopic supernovae) in terms of energetics and observed redshift distribution, indicating a continuous distribution overall. © 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A
Photospheric and chromospheric activity on EY Dra
Magnetic activity in the photosphere and chromosphere of the M dwarf EY Dra
is studied and possible correlations between the two are investigated using
photometric observations in the V and R bands and optical and near infrared
spectroscopy. The longitudinal spot configuration in the photosphere is
obtained from the V band photometry, and the chromospheric structures are
investigated using variations in the H alpha line profile and observations of
the Paschen beta line. The shape of the V band light-curve indicates two active
regions on the stellar surface, about 0.4 in phase apart. The spectroscopic
observations show enhanced H alpha emission observed close to the phases of the
photometrically detected starspots. This could indicate chromospheric plages
associated with the photospheric starspots. Some indications of prominence
structures are also seen. The chromospheric pressure is limited to logTR < -4
based on the non-detection of emission in the Paschen beta wavelength region.Comment: 7 pages, 7 figures, accepted for publication in Astronomische
Nachrichten (Astronomical Notes
The afterglows of Swift-era GRBs. I.
VizieR online Data Catalogue associated with article published in journal Astronomical Journal (AAS) with title \u27The afterglows of Swift-era gamma-ray bursts. I. Comparing pre-Swift and Swift-era Long/Soft (Type II) GRB optical afterglows.\u27 (bibcode: 2010ApJ...720.1513K
CFHTLenS: The Canada-France-Hawaii Telescope Lensing Survey - Imaging Data and Catalogue Products
We present data products from the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS). CFHTLenS is based on the Wide component of the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). It encompasses 154 deg^2 of deep, optical, high-quality, sub-arcsecond imaging data in the five optical filters u^*g'r'i'z'. The article presents our data processing of the complete CFHTLenS data set. We were able to obtain a data set with very good image quality and high-quality astrometric and photometric calibration. Our external astrometric accuracy is between 60-70 mas with respect to SDSS data and the internal alignment in all filters is around 30 mas. Our average photometric calibration shows a dispersion on the order of 0.01 to 0.03 mag for g'r'i'z' and about 0.04 mag for u^* with respect to SDSS sources down to i <= 21. In the spirit of the CFHTLS all our data products are released to the astronomical community via the Canadian Astronomy Data Centre. We give a description and how-to manuals of the public products which include image pixel data, source catalogues with photometric redshift estimates and all relevant quantities to perform weak lensing studies
CFHTLenS: the Canada-France-Hawaii Telescope Lensing Survey - imaging data and catalogue products
International audienceWe present data products from the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS). CFHTLenS is based on the Wide component of the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). It encompasses 154 deg2 of deep, optical, high-quality, sub-arcsecond imaging data in the five optical filters u*g'r'i'z'. The scientific aims of the CFHTLenS team are weak gravitational lensing studies supported by photometric redshift estimates for the galaxies. This paper presents our data processing of the complete CFHTLenS data set. We were able to obtain a data set with very good image quality and high-quality astrometric and photometric calibration. Our external astrometric accuracy is between 60 and 70 mas with respect to Sloan Digital Sky Survey (SDSS) data, and the internal alignment in all filters is around 30 mas. Our average photometric calibration shows a dispersion of the order of 0.01-0.03 mag for g'r'i'z' and about 0.04 mag for u* with respect to SDSS sources down to iSDSS ≤ 21. We demonstrate in accompanying papers that our data meet necessary requirements to fully exploit the survey for weak gravitational lensing analyses in connection with photometric redshift studies. In the spirit of the CFHTLS, all our data products are released to the astronomical community via the Canadian Astronomy Data Centre at http://www.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/community/CFHTLens/query.html. We give a description and how-to manuals of the public products which include image pixel data, source catalogues with photometric redshift estimates and all relevant quantities to perform weak lensing studies