908 research outputs found
Detection of Dark Matter Concentrations in the Field of Cl 1604+4304 from Weak Lensing Analysis
We present a weak-lensing analysis of a region around the galaxy cluster Cl
1604+4304 (z=0.897) on the basis of the deep observations with the HST/WFPC2.
We apply a variant of Schneider's aperture mass technique to the observed WFPC2
field and obtain the distribution of weak-lensing signal-to-noise (S/N) ratio
within the field. The resulting S/N map reveals a clear pronounced peak located
about 1.7 arcmin (850h_{50}^{-1} kpc at z=0.897) southwest of the second peak
associated with the optical cluster center determined from the dynamical
analysis of Postman et al. A non-linear finite-field inversion method has been
used to reconstruct the projected mass distribution from the observed shear
field. The reconstructed mass map shows a super-critical feature at the
location of the S/N peak as well as in the cluster central region. Assuming the
redshift distribution of field galaxies, we obtain the total mass in the
observed field to be 1.0 h_{50}^{-1} 10^{15} M_sun for =1.0. The estimated
mass within a circular aperture of radius 280h_{50}^{-1} kpc centered on the
dark clump is 2.4h_{50}^{-1} 10^{14} M_sun. We have confirmed the existence of
the ` dark ' mass concentration from another deep HST observation with a
slightly different ~20 arcsec pointing.Comment: 7 pages, 3 figure
Fast high-efficiency integrated waveguide photodetectors using novel hybrid vertical/butt coupling geometry
We report a novel coupling geometry for integrated waveguide photodetectorsâa hybrid vertical coupling/butt coupling scheme that allows the integration of fast, efficient, photodetectors with conventional double heterostructure waveguides. It can be employed to yield a planar, or pseudo-planar, surface that supports further levels of integration. The approach is demonstrated with a 25-”m-long p-i-n detector integrated with an InP/InGaAsP/InP waveguide, which displays a high (~90%) efficiency and large (~15 GHz) bandwidth. This is the fastest high-efficiency integrated waveguide photodetector reported to date
Mass-detection of a matter concentration projected near the cluster Abell 1942: Dark clump or high-redshift cluster?
A weak-lensing analysis of wide-field - and -band images centered on
the cluster Abell 1942 has uncovered a mass concentration arcminutes
South of the cluster center. A statistical analysis shows that the detections
are highly significant. No strong concentration of bright galaxies is seen at
the position of the mass concentration, though a slight galaxy number
overdensity and a weak extended X-ray source are present about 1' away from its
center.
From the spatial dependence of the tangential alignment around the center of
the mass concentration, we inferred a lower bound on the mass inside a sphere
of radius \ts Mpc of , much higher
than crude mass estimates based on X-ray data. No firm conclusion can be
inferred about the nature of the clump. If it were a high-redshift cluster, the
weak X-ray flux would indicate that it had an untypically low X-ray luminosity
for its mass; if the X-ray emission were physically unrelated to the mass
concentration, this conclusion would be even stronger.
The search for massive halos by weak lensing enables us for the first time to
select halos based on their mass properties only and to detect new types of
objects, e.g., dark halos. The mass concentration in the field of A1942 may be
the first example of such a halo.Comment: Sumitted to A&A Main Journal. 15 pages, 11 figures. 75 Kb gzipped tar
file. Figures with images not included, but available on ftp.iap.fr
/pub/from_users/mellier/A1942: a1942darkclump.ps.gz (2.1 Mb
Lensing Magnification: A novel method to weigh high-redshift clusters and its application to SpARCS
We introduce a novel method to measure the masses of galaxy clusters at high
redshift selected from optical and IR Spitzer data via the red-sequence
technique. Lyman-break galaxies are used as a well understood, high-redshift
background sample allowing mass measurements of lenses at unprecedented high
redshifts using weak lensing magnification. By stacking a significant number of
clusters at different redshifts with average masses of ~1-3x10^14M_sun, as
estimated from their richness, we can calibrate the normalisation of the
mass-richness relation. With the current data set (area: 6 deg^2) we detect a
magnification signal at the >3-sigma level. There is good agreement between the
masses estimated from the richness of the clusters and the average masses
estimated from magnification, albeit with large uncertainties. We perform tests
that suggest the absence of strong systematic effects and support the
robustness of the measurement. This method - when applied to larger data sets
in the future - will yield an accurate calibration of the mass-observable
relations at z>~1 which will represent an invaluable input for cosmological
studies using the galaxy cluster mass function and astrophysical studies of
cluster formation. Furthermore this method will probably be the least expensive
way to measure masses of large numbers of z>1 clusters detected in future
IR-imaging surveys.Comment: 5 pages, 1 figure, 1 table, accepted by ApJL, minor revision
Die Entwicklung des Arzneimittelverbrauchs unter besonderer BerĂŒcksichtigung demographischer Faktoren
ESO Imaging Survey VII. Distant Cluster Candidates over 12 square degrees
In this paper the list of candidate clusters identified from the I-band data
of the ESO Imaging Survey (EIS) is completed using the images obtained over a
total area of about 12 square degrees. Together with the data reported earlier
the total I-band coverage of EIS is 17 square degrees, which has yielded a
sample of 252 cluster candidates in the redshift range 0.2 \lsim z \lsim 1.3.
This is the largest optically-selected sample currently available in the
Southern Hemisphere. It is also well distributed in the sky thus providing
targets for a variety of VLT programs nearly year round.Comment: 5 pages, 3 figures, submitted to Astronomy & Astrophysic
First Galaxy-Galaxy Lensing Measurement of Satellite Halo Mass in the CFHT Stripe-82 Survey
We select satellite galaxies from the galaxy group catalog constructed with
the SDSS spectroscopic galaxies and measure the tangential shear around these
galaxies with source catalog extracted from CFHT/MegaCam Stripe-82 Survey to
constrain the mass of subhalos associated with them. The lensing signal is
measured around satellites in groups with masses in the range [10^{13},
5x10^{14}]h^{-1}M_{sun}, and is found to agree well with theoretical
expectation. Fitting the data with a truncated NFW profile, we obtain an
average subhalo mass of log M_{sub}= 11.68 \pm 0.67 for satellites whose
projected distances to central galaxies are in the range [0.1, 0.3] h^{-1}Mpc,
and log M_{sub}= 11.68 \pm 0.76 for satellites with projected halo-centric
distance in [0.3, 0.5] h^{-1}Mpc. The best-fit subhalo masses are comparable to
the truncated subhalo masses assigned to satellite galaxies using abundance
matching and about 5 to 10 times higher than the average stellar mass of the
lensing satellite galaxies.Comment: 7 pages, 4 figures, accepted by MNRA
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