1,151 research outputs found
Deep Imaging of the Double Quasar 0957+561: New Constraints on H_0
We present new results from extremely deep, high-resolution images of the
field around the double quasar QSO 0957+561. A possible gravitational arc
system near the double quasar has recently been reported, which, if real, would
set strong constraints on determinations of the Hubble constant from the time
delay in the double quasar. We find that both the morphology and the colors of
the claimed arc systems suggest that they are chance alignments of three and
two different objects, and not gravitationally lensed arcs. Hence, the
constraints on -determinations from the arcs are not valid. Also, a small
group of galaxies at near the line-of-sight which was required to have
a very large mass in the physically interesting arc models, is most likely
insignificant. From our deep images we are able to use weak lensing of faint
background galaxies in the field to map the gravitational potential in the main
cluster. This sets new constraints on determinations of . We find that the
Hubble constant is constrained to be less than 70km/(s Mpc), if the time delay
between the two images of the QSO is equal to or larger than 1.1 years.Comment: (uuencoded and compressed postscipt including 3 figures); 14 page
The Density Profile of Cluster-scale Dark Matter Halos
We measure the average gravitational shear profile of 6 massive clusters
(M_vir ~ 10^15 M_sun) at z=0.3 out to a radius ~2h^-1 Mpc. The measurements are
fitted to a generalized NFW-like halo model \rho(r) with an arbitrary r -> 0
slope \alpha. The data are well fitted by such a model with a central cusp with
\alpha ~ 0.9 - 1.6 (68% confidence interval). For the standard-NFW case \alpha
= 1.0, we find a concentration parameter c_vir that is consistent with recent
predictions from high-resolution CDM N-body simulations. Our data are also well
fitted by an isothermal sphere model with a softened core. For this model, our
1\sigma upper limit for the core radius corresponds to a limit \sigma_star \leq
0.1 cm^2 g^-1 on the elastic collision cross-section in a self-interacting dark
matter model.Comment: 4 pages, 3 figures; version accepted for publication by ApJ Letters.
Three figures omitted to allow space for new fig. 3 and expanded results and
discussion sections, including NSIS model fi
Calibration of the Mass-Temperature Relation for Clusters of Galaxies Using Weak Gravitational Lensing
The main uncertainty in current determinations of the power spectrum
normalization, sigma_8, from abundances of X-ray luminous galaxy clusters
arises from the calibration of the mass-temperature relation. We use our weak
lensing mass determinations of 30 clusters from the hitherto largest sample of
clusters with lensing masses, combined with X-ray temperature data from the
literature, to calibrate the normalization of this relation at a temperature of
8 keV, M_{500c,8 keV}=(8.7 +/- 1.6) h^{-1} 10^{14} M_sun. This normalization is
consistent with previous lensing-based results based on smaller cluster
samples, and with some predictions from numerical simulations, but higher than
most normalizations based on X-ray derived cluster masses. Assuming the
theoretically expected slope alpha=3/2 of the mass-temperature relation, we
derive sigma_8 = 0.88 +/-0.09 for a spatially-flat LambdaCDM universe with
Omega_m = 0.3. The main systematic errors on the lensing masses result from
extrapolating the cluster masses beyond the field-of-view used for the
gravitational lensing measurements, and from the separation of
cluster/background galaxies, contributing each with a scatter of 20%. Taking
this into account, there is still significant intrinsic scatter in the
mass-temperature relation indicating that this relation may not be very tight,
at least at the high mass end. Furthermore, we find that dynamically relaxed
clusters are 75 +/-40% hotter than non-relaxed clusters.Comment: 8 pages, 4 figures, revised version submitted to Ap
Time Delay Measurements for the Cluster-lensed Sextuple Quasar SDSS J2222+2745
We report first results from an ongoing monitoring campaign to measure time
delays between the six images of the quasar SDSS\,J22222745, gravitationally
lensed by a galaxy cluster. The time delay between A and B, the two most highly
magnified images, is measured to be days (95\%
confidence interval), consistent with previous model predictions for this lens
system. The strong intrinsic variability of the quasar also allows us to derive
a time delay value of days between image C and A,
in spite of modest overlap between their light curves in the current data set.
Image C, which is predicted to lead all the other lensed quasar images, has
undergone a sharp, monotonic flux increase of 60-75\% during 2014. A
corresponding brightening is firmly predicted to occur in images A and B during
2016. The amplitude of this rise indicates that time delays involving all six
known images in this system, including those of the demagnified central images
D-F, will be obtainable from further ground-based monitoring of this system
during the next few years.Comment: 9 pages, 9 figures, Version accepted for publication in Ap
On the lack of correlation between Mg II 2796, 2803 Angstrom and Lyman alpha emission in lensed star-forming galaxies
We examine the Mg II 2796, 2803 Angstrom, Lyman alpha, and nebular line
emission in five bright star-forming galaxies at 1.66<z<1.91 that have been
gravitationally lensed by foreground galaxy clusters. All five galaxies show
prominent Mg II emission and absorption in a P Cygni profile. We find no
correlation between the equivalent widths of Mg II and Lyman alpha emission.
The Mg II emission has a broader range of velocities than do the nebular
emission line profiles; the Mg II emission is redshifted with respect to
systemic by 100 to 200 km/s. When present, Lyman alpha is even more redshifted.
The reddest components of Mg II and Lyman alpha emission have tails to 500-600
km/s, implying a strong outflow. The lack of correlation in the Mg II and Lyman
alpha equivalent widths, the differing velocity profiles, and the high ratios
of Mg II to nebular line fluxes together suggest that the bulk of Mg II
emission does not ultimately arise as nebular line emission, but may instead be
reprocessed stellar continuum emission.Comment: The Astrophysical Journal, in press. 6 pages, 2 figure
Searching for decaying axion-like dark matter from clusters of galaxies
We consider the possibility of constraining the lifetime of radiatively
decaying dark matter particles in clusters of galaxies inspired from generic
axions of the Kaluza-Klein type. Such axions have been invoked as a possible
explanation for the coronal X-ray emission from the Sun. These axions, or
similar particles, can be produced inside stars and some of them remain
confined by the deep gravitational potential of clusters of galaxies.
Specifically, we consider regions within merging galaxy clusters (Abell 520 and
the "Bullet Cluster"), where gravitational lensing observations have identified
massive, but baryon poor, structures. From an analysis of X-ray observations of
these mass concentrations, and the expected photon spectrum of decaying solar
KK-axions, we derive lower limits to the lifetime of such axions of tau approx.
10^23 sec. However, if KK-axions constitute less than a few percent of the dark
matter mass, this lifetime constraint is similar to that derived from solar
KK-axions.Comment: Submitted to PRL, 4 pages, 3 figure
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