32 research outputs found
Strong Lensing Analysis of the Cluster RCS0224-0002 at
We present a detailed mass reconstruction of the cluster RCS0224-0002 at
from the strong lensing features observed with HST/WFPC2. The mass
profile is reconstructed using a parametric approach. We introduce a novel
method to fit extended multiple images based on the Modified Hausdorff Distance
between observed arcs and the arcs reproduced by the model. We perform the
detailed error analysis of the model parameter using the MCMC method. Our model
reproduces all the observed strong lensing features of the RCS0224-0002 and
predicts the redshift of one of the arcs systems to be (the
other system has an spectroscopic redshift of ). The reconstructed
inner mass profile is well fitted by a non-singular isothermal sphere, rather
than with an NFW model. Dark matter substructure, derived from the light
distribution of the most luminous cluster members, is crucial for reproducing
the complexity of the quadrupole image system, which could not be achieved
otherwise. The reconstructed mass distribution closely follows the light,
however it is significantly shifted from the X-ray emission of the gas. The
mass of RCS0224-0002 derived from the lensing model, is in a very good agreement with the one obtained from the X-ray
temperature measured with deep Chandra observations.Comment: 13 pages, accepted for A&
The Strongly Polarized Afterglow of GRB 020405
We report polarization measurements and photometry for the optical afterglow
of the gamma-ray burst GRB 020405. We measured a highly significant 9.9%
polarization (in V band) 1.3 days after the burst and argue that it is
intrinsic to the GRB. The light curve decay is well fitted by a
power-law; we do not see any evidence for a break between 1.24 and 4.3 days
after the burst. We discuss these measurements in the light of several models
of GRB afterglows.Comment: submitted to ApJ
Spectroscopy of the neighboring massive clusters Abell 222 and Abell 223
We present a spectroscopic catalog of the neighboring massive clusters Abell
222 and Abell 223. The catalog contains the positions, redshifts, R magnitudes,
V-R color, as well as the equivalent widths for a number of lines for 183
galaxies, 153 of them belonging to the A 222 and A 223 system. We determine the
heliocentric redshifts to be z=0.2126+/-0.0008 for A 222 and z=0.2079+/-0.0008
for A 223. The velocity dispersions of both clusters in the cluster restframe
are about the same: sigma = 1014^{+90}_{-71} km/s and sigma = 1032^{+99}_{-76}
km/s for A 222 and A 223, respectively. While we find evidence for substructure
in the spatial distribution of A 223, no kinematic substructure can be
detected. From the red cluster sequence identified in a
color--magnitude--diagram we determine the luminosity of both clusters and
derive mass--to--light ratios in the R--band of (M/L)_A222 = (202+/-43) h_70
M_{su}n/L_{sun} and (M/L)_A223 = (149+/-33) h_70 M_{sun}/L_{sun}. Additionally
we identify a group of background galaxies at z ~ 0.242.Comment: Accepted for publication in A&A, 10 pages, 9 figures, full version of
table 2 included in source distribution, version with higher quality images
available from http://www.astro.uni-bonn.de/~dietrich
Mass-to-Light Ratios of Groups and Clusters of Galaxies
We constrain the mass-to-light ratios, gas mass fractions, baryon mass
fractions and the ratios of total to luminous mass for a sample of eight nearby
relaxed galaxy groups and clusters: A262, A426, A478, A1795, A2052, A2063,
A2199 and MKW4s. We use ASCA spatially resolved spectroscopic X-ray
observations and ROSAT PSPC images to constrain the total and gas masses of
these clusters. To measure cluster luminosities we use galaxy catalogs
resulting from the digitization and automated processing of the second
generation Palomar Sky Survey plates calibrated with CCD images in the
Gunn-Thuan g, r, and i bands.
Under the assumption of hydrostatic equilibrium and spherical symmetry, we
can measure the total masses of clusters from their intra-cluster gas
temperature and density profiles. Spatially resolved ASCA spectra show that the
gas temperature decreases with increasing distance from the center. By
comparison, the assumption that the gas is isothermal results in an
underestimate of the total mass at small radii, and an overestimate at large
cluster radii.
We have obtained luminosity functions for all clusters in our sample. After
correcting for background and foreground galaxies, we estimate the total
cluster luminosity using Schechter function fits to the galaxy catalogs. In the
three lowest redshift clusters where we can sample to fainter absolute
magnitudes, we have detected a flattening of the luminosity function at
intermediate magnitudes and a rise at the faint end. These clusters were fit
with a sum of two Schechter functions. The remaining clusters were well fit
with a single Schechter function.Comment: 11 pages 5 figures, accepted for publication in the Ap
The near-infrared luminosity function of cluster galaxies beyond redshift one
We determined the K band luminosity function (LF) of cluster galaxies at
redshift z~1.2, using near-infrared images of three X-ray luminous clusters at
z=1.11,1.24,1.27. The composite LF was derived down to M*+4, by means of
statistical background subtraction, and is well described by a Schechter
function with K*=20.5 AB mag and alpha=-1.
From the K band composite LF we derived the stellar mass function of cluster
galaxies. Using available X-ray mass profiles we determined the M/L ratios of
these three clusters, which tend to be lower than those measured in the local
universe.
With these data, no significant difference can be seen between the shapes of
the cluster galaxies LF and the LF of field galaxies at similar redshift.
We also found no significant evolution out to z ~1.2 in the bright (<M*+4)
part of the cluster galaxies LF probed in this study, apart from a brightening
of ~1.3 mag of the characteristic magnitude of the high redshift LF. We
confirm, and extend to higher redshift, the result from previous work that the
redshift evolution of the characteristic magnitude M* is consistent with
passive evolution of a stellar population formed at z>2.
The results obtained in this work support and extend previous findings that
most of the stars in bright galaxies were formed at high redshift, and that
K-bright (M>10^11 Msun) galaxies were already in place at z ~ 1.2, at least in
the central regions of X-ray luminous clusters. Together with recent results on
the field galaxies stellar mass function, this implies that most of the stellar
mass is already assembled in massive galaxies by z ~ 1, both in low and high
density environments.Comment: 16 pages, 10 figures, to appear in A&
Planets in Stellar Clusters Extensive Search. III. A search for transiting planets in the metal-rich open cluster NGC 6791
We have undertaken a long-term project, Planets in Stellar Clusters Extensive
Search (PISCES), to search for transiting planets in open clusters. In this
paper we present the results for NGC 6791 -- a very old, populous, metal rich
cluster. We have monitored the cluster for over 300 hours, spread over 84
nights. We have not detected any good transiting planet candidates. Given the
photometric precision and temporal coverage of our observations, and current
best estimates for the frequency and radii of short-period planets, the
expected number of detectable transiting planets in our sample is 1.5. We have
discovered 14 new variable stars in the cluster, most of which are eclipsing
binaries, and present high precision light curves, spanning two years, for
these new variables and also the previously known variables.Comment: 18 pages LaTeX, including 11 figures and 6 tables. Limb darkening
included in the computation of the planet detection efficiency. Version with
full resolution figures available through ftp at
ftp://cfa-ftp.harvard.edu/pub/bmochejs/PISCES/papers/3_N6791
Recommended from our members
Annotation of the Drosophila melanogaster euchromatic genome: a systematic review
BACKGROUND: The recent completion of the Drosophila melanogaster genomic sequence to high quality and the availability of a greatly expanded set of Drosophila cDNA sequences, aligning to 78% of the predicted euchromatic genes, afforded FlyBase the opportunity to significantly improve genomic annotations. We made the annotation process more rigorous by inspecting each gene visually, utilizing a comprehensive set of curation rules, requiring traceable evidence for each gene model, and comparing each predicted peptide to SWISS-PROT and TrEMBL sequences. RESULTS: Although the number of predicted protein-coding genes in Drosophila remains essentially unchanged, the revised annotation significantly improves gene models, resulting in structural changes to 85% of the transcripts and 45% of the predicted proteins. We annotated transposable elements and non-protein-coding RNAs as new features, and extended the annotation of untranslated (UTR) sequences and alternative transcripts to include more than 70% and 20% of genes, respectively. Finally, cDNA sequence provided evidence for dicistronic transcripts, neighboring genes with overlapping UTRs on the same DNA sequence strand, alternatively spliced genes that encode distinct, non-overlapping peptides, and numerous nested genes. CONCLUSIONS: Identification of so many unusual gene models not only suggests that some mechanisms for gene regulation are more prevalent than previously believed, but also underscores the complex challenges of eukaryotic gene prediction. At present, experimental data and human curation remain essential to generate high-quality genome annotations
CfA3: 185 Type Ia Supernova Light Curves from the CfA
We present multi-band photometry of 185 type-Ia supernovae (SN Ia), with over
11500 observations. These were acquired between 2001 and 2008 at the F. L.
Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics (CfA).
This sample contains the largest number of homogeneously-observed and reduced
nearby SN Ia (z < 0.08) published to date. It more than doubles the nearby
sample, bringing SN Ia cosmology to the point where systematic uncertainties
dominate. Our natural system photometry has a precision of 0.02 mag or better
in BVRIr'i' and roughly 0.04 mag in U for points brighter than 17.5 mag. We
also estimate a systematic uncertainty of 0.03 mag in our SN Ia standard system
BVRIr'i' photometry and 0.07 mag for U. Comparisons of our standard system
photometry with published SN Ia light curves and comparison stars, where
available for the same SN, reveal agreement at the level of a few hundredths
mag in most cases. We find that 1991bg-like SN Ia are sufficiently distinct
from other SN Ia in their color and light-curve-shape/luminosity relation that
they should be treated separately in light-curve/distance fitter training
samples. The CfA3 sample will contribute to the development of better
light-curve/distance fitters, particularly in the few dozen cases where
near-infrared photometry has been obtained and, together, can help disentangle
host-galaxy reddening from intrinsic supernova color, reducing the systematic
uncertainty in SN Ia distances due to dust.Comment: Accepted to the Astrophysical Journal. Minor changes from last
version. Light curves, comparison star photometry, and passband tables are
available at http://www.cfa.harvard.edu/supernova/CfA3
Interaction of HIF and USF signaling pathways at human genes flanked by hypoxia-response elements and E-box palindromes
Rampant activity of the hypoxia-inducible factor (HIF)-1 in cancer is frequently associated with the malignant progression into a harder-to-treat, increasingly aggressive phenotype. Clearly, anti-HIF strategies in cancer cells are of considerable clinical interest. One way to fine-tune, or inhibit, HIF's transcriptional outflow independently of hydroxylase activities could be through competing transcription factors. A CACGTG-binding activity in human hepatoma cells was previously found to restrict HIF's access to hypoxia response cis-elements (HRE) in a Daphnia globin gene promoter construct (phb2). The CACGTG factor, and its impact on hypoxia-responsive human genes, was analyzed in this study by genome-wide computational scans as well as gene-specific quantitative PCR, reporter and DNA-binding assays in hepatoma (Hep3B), cervical carcinoma (HeLa), and breast carcinoma (MCF7) cells. Among six basic helix-loop-helix transcription factors known to target CACGTG palindromes, we identified upstream stimulatory factor (USF)-1/2 as predominant phb2 CACGTG constituents in Hep3B, HeLa, and MCF7 cells. Human genes with adjacent or overlapping HRE and CACGTG motifs included with lactate dehydrogenase A (LDHA) and Bcl-2/E1B 19 kDa interacting protein 3 (BNIP3) hypoxia-induced HIF-1 targets. Parallel recruitment of HIF-1α and USF1/2a to the respective promoter chromatin was verified for all cell lines investigated. Mutual complementing (LDHA) or moderating (BNIP3) cross-talk was seen upon overexpression or silencing of HIF-1α and USF1/2a. Distinct (LDHA) or overlapping (BNIP3) promoter-binding sites for HIF-1 and USFs were subsequently characterized. We propose that, depending on abundance or activity of its protein constituents, O(2)-independent USF signaling can function to fine-tune or interfere with HIF-mediated transcription in cancer cells. Mol Cancer Res; 1-17. ©2011 AACR
Koncepce moznosti reseni sirokopasmovych antennich systemu pro simulatory radiolokacnich signalu.
Different possibilities of antennas for personal radar signal testers were studied.Available from STL Prague, CZ / NTK - National Technical LibrarySIGLECZCzech Republi