402 research outputs found
Galaxy Halo Masses from Galaxy-Galaxy Lensing
We present measurements of the extended dark halo profiles of bright early
type galaxies at redshifts 0.1 to 0.9 obtained via galaxy-galaxy lensing
analysis of images taken at the CFHT using the UH8K CCD mosaic camera. Six half
degree fields were observed for a total of 2 hours each in I and V, resulting
in catalogs containing ~20 000 galaxies per field. We used V-I color and I
magnitude to select bright early type galaxies as the lens galaxies, yielding a
sample of massive lenses with fairly well determined redshifts and absolute
magnitudes M ~ M_* \pm 1. We paired these with faint galaxies lying at angular
distances 20" to 60", corresponding to physical radii of 26 to 77 kpc (z = 0.1)
and 105 to 315 kpc (z = 0.9), and computed the mean tangential shear of the
faint galaxies. The shear falls off with radius roughly as expected for flat
rotation curve halos. The shear values were weighted in proportion to the
square root of the luminosity of the lens galaxy. Our results give a value for
the average mean rotation velocity of an L_* galaxy halo at r~50-200 kpc of v_*
= 238^{+27}_{-30} km per sec for a flat lambda (Omega_m0 = 0.3, Omega_l0 = 0.7)
cosmology (v_* = 269^{+34}_{-39} km per sec for Einstein-de Sitter), and with
little evidence for evolution with redshift. We compare to halo masses measured
by other groups/techniques. We find a mass-to-light ratio of ~121\pm28h(r/100
kpc) and these halos constitute Omega ~0.04 \pm 0.01(r/100 kpc) of closure
density. (abridged)Comment: Accepted for publication in ApJ (minor modifications) - 32 pages, 11
figs, 5 table
Constraints On the Size Evolution of Brightest Cluster Galaxies
We measure the luminosity profiles of 16 brightest cluster galaxies (BCGs) at
using high resolution F160W NICMOS and F814W WFPC2 HST imaging.
The heterogeneous sample is drawn from a variety of surveys: seven from
clusters in the Einstein Medium Sensitivity Survey, five from the Las Campanas
Distant Cluster Survey and its northern hemisphere precursor, and the remaining
four from traditional optical surveys. We find that the surface brightness
profiles of all but three of these BCGs are well described by a standard de
Vaucouleurs () profile out to at least and that the
biweight-estimated NICMOS effective radius of our high redshift BCGs ( kpc for km s Mpc, ) is times smaller than that measured for a local
BCG sample. If high redshift BCGs are in dynamical equilibrium and satisfy the
same scaling relations as low redshift ones, this change in size would
correspond to a mass growth of a factor of 2 since . However, the
biweight-estimated WFPC2 effective radius of our sample is 18 5.1 kpc,
which is fully consistent with the local sample. While we can rule out mass
accretion rates higher than a factor of 2 in our sample, the discrepancy
between our NICMOS and WFPC2 results, which after various tests we describe
appears to be physical, does not yet allow us to place strong constraints on
accretion rates below that level.Comment: ApJ accepted (566, 1, February 2002), 12 pages, uses emulateapj5.st
The complex hodological architecture of the macaque dorsal intraparietal areas as emerging from neural tracers and dw-mri tractography
In macaque monkeys, dorsal intraparietal areas are involved in several daily visuomotor actions. However, their border and sources of cortical afferents remain loosely defined. Combining retrograde histologic tracing and MRI diffusion-based tractography, we found a complex hodology of the dorsal bank of the intraparietal sulcus (db-IPS), which can be subdivided into a rostral intraparietal area PEip, projecting to the spinal cord, and a caudal medial intraparietal area MIP lacking such projections. Both include an anterior and a posterior sector, emerging from their ipsilateral, gradient-like connectivity profiles. As tractography estimations, we used the cross-sectional area of the white matter bundles connecting each area with other parietal and frontal regions, after selecting regions of interest (ROIs) corresponding to the injection sites of neural tracers. For most connections, we found a significant correlation between the proportions of cells projecting to all sectors of PEip and MIP along the continuum of the db-IPS and tractography. The latter also revealed “false positive” but plausible connections awaiting histologic validation
Transients from initial conditions based on Lagrangian perturbation theory in N-body simulations
We explore the initial conditions for cosmological N-body simulations
suitable for calculating the skewness and kurtosis of the density field. In
general, the initial conditions based on the perturbation theory (PT) provide
incorrect second-order and higher-order growth. These errors implied by the use
of the perturbation theory to set up the initial conditions in N-body
simulations are called transients. Unless these transients are completely
suppressed compared with the dominant growing mode, we can not reproduce the
correct evolution of cumulants with orders higher than two, even though there
is no problem with the numerical scheme. We investigate the impact of
transients on the observable statistical quantities by performing -body
simulations with initial conditions based on Lagrangian perturbation theory
(LPT). We show that the effects of transients on the kurtosis from the initial
conditions, based on second-order Lagrangian perturbation theory (2LPT) have
almost disappeared by , as long as the initial conditions are set at . This means that for practical purposes, the initial conditions based on
2LPT are accurate enough for numerical calculations of skewness and kurtosis.Comment: 21 pages, 5 figures; accepted for publication in JCA
The Galactic Exoplanet Survey Telescope (GEST)
The Galactic Exoplanet Survey Telescope (GEST) will observe a 2 square degree
field in the Galactic bulge to search for extra-solar planets using a
gravitational lensing technique. This gravitational lensing technique is the
only method employing currently available technology that can detect Earth-mass
planets at high signal-to-noise, and can measure the frequency of terrestrial
planets as a function of Galactic position. GEST's sensitivity extends down to
the mass of Mars, and it can detect hundreds of terrestrial planets with
semi-major axes ranging from 0.7 AU to infinity. GEST will be the first truly
comprehensive survey of the Galaxy for planets like those in our own Solar
System.Comment: 17 pages with 13 figures, to be published in Proc. SPIE vol 4854,
"Future EUV-UV and Visible Space Astrophysics Missions and Instrumentation
A New Strategy for Deep Wide-Field High Resolution Optical Imaging
We propose a new strategy for obtaining enhanced resolution (FWHM = 0.12
arcsec) deep optical images over a wide field of view. As is well known, this
type of image quality can be obtained in principle simply by fast guiding on a
small (D = 1.5m) telescope at a good site, but only for target objects which
lie within a limited angular distance of a suitably bright guide star. For high
altitude turbulence this 'isokinetic angle' is approximately 1 arcminute. With
a 1 degree field say one would need to track and correct the motions of
thousands of isokinetic patches, yet there are typically too few sufficiently
bright guide stars to provide the necessary guiding information. Our proposed
solution to these problems has two novel features. The first is to use
orthogonal transfer charge-coupled device (OTCCD) technology to effectively
implement a wide field 'rubber focal plane' detector composed of an array of
cells which can be guided independently. The second is to combine measured
motions of a set of guide stars made with an array of telescopes to provide the
extra information needed to fully determine the deflection field. We discuss
the performance, feasibility and design constraints on a system which would
provide the collecting area equivalent to a single 9m telescope, a 1 degree
square field and 0.12 arcsec FWHM image quality.Comment: 46 pages, 22 figures, submitted to PASP, a version with higher
resolution images and other supplementary material can be found at
http://www.ifa.hawaii.edu/~kaiser/wfhr
A weak lensing analysis of the Abell 383 cluster
In this paper we use deep CFHT and SUBARU archival images of the
Abell 383 cluster (z=0.187) to estimate its mass by weak lensing. To this end,
we first use simulated images to check the accuracy provided by our KSB
pipeline. Such simulations include both the STEP 1 and 2 simulations, and more
realistic simulations of the distortion of galaxy shapes by a cluster with a
Navarro-Frenk-White (NFW) profile. From such simulations we estimate the effect
of noise on shear measurement and derive the correction terms. The R-band image
is used to derive the mass by fitting the observed tangential shear profile
with a NFW mass profile. Photometric redshifts are computed from the uBVRIz
catalogs. Different methods for the foreground/background galaxy selection are
implemented, namely selection by magnitude, color and photometric redshifts,
and results are compared. In particular, we developed a semi-automatic
algorithm to select the foreground galaxies in the color-color diagram, based
on observed colors. Using color selection or photometric redshifts improves the
correction of dilution from foreground galaxies: this leads to higher signals
in the inner parts of the cluster. We obtain a cluster mass that is ~ 20%
higher than previous estimates, and is more consistent the mass expected from
X--ray data. The R-band luminosity function of the cluster is finally computed.Comment: 11 pages, 12 figures. Accepted for publication on Astronomy &
Astrophysic
- …