16 research outputs found
Mass and Light in the Universe
We present a weak lensing and photometric study of six half by half degree
fields observed at the CFHT using the UH8K CCD mosaic camera. The fields were
observed for a total of 2 hours each in I and V, resulting in catalogs
containing ~ 20 000 galaxies per passband per field. We use V-I color and I
magnitude to select bright early type galaxies at redshifts 0.1 < z < 0.9. We
measure the gravitational shear from faint galaxies in the range 21 < m_I < 25
from a composite catalog and find a strong correlation with that predicted from
the early types if they trace the mass with mass-to-light ratio 300\pm75 h (in
solar units) for a flat (Omega_m0 = 0.3, Omega_l0 = 0.7) lambda cosmology and
400\pm100 h for Einstein-de Sitter. We make two-dimensional reconstructions of
the mass surface density. Cross-correlation of the measured mass surface
density with that predicted from the early type galaxy distribution shows a
strong peak at zero lag (significant at the 5.2-sigma level). We azimuthally
average the cross- and auto-correlation functions. We conclude that the
profiles are consistent with early type galaxies tracing mass on scales of > 45
arcsec (> 200 kpc at z = 0.5). We sub-divide our bright early type galaxies by
redshift and obtain similar conclusions. These mass-to-light ratios imply
\Omega_m0 = 0.10\pm0.02 (\Omega_m0 = 0.13\pm0.03 for Einstein-de Sitter) of
closure density.Comment: 27 pages, 19 figs (4 ps, 15 gif), 4 tables, accepted for publication
in Ap.J. (email Gillian for better resolution ps versions of gif greyscale
plots
The Infrared Surface Brightness Fluctuation Distances to the Hydra and Coma Clusters
We present IR surface brightness fluctuation (SBF) distance measurements to
NGC 4889 in the Coma cluster and to NGC 3309 and NGC 3311 in the Hydra cluster.
We explicitly corrected for the contributions to the fluctuations from globular
clusters, background galaxies, and residual background variance. We measured a
distance of 85 +/- 10 Mpc to NGC 4889 and a distance of 46 +/- 5 Mpc to the
Hydra cluster. Adopting recession velocities of 7186 +/- 428 km/s for Coma and
4054 +/- 296 km/s for Hydra gives a mean Hubble constant of H_0 = 87 +/- 11
km/s/Mpc. Corrections for residual variances were a significant fraction of the
SBF signal measured, and, if underestimated, would bias our measurement towards
smaller distances and larger values of H_0. Both NICMOS on the Hubble Space
Telescope and large-aperture ground-based telescopes with new IR detectors will
make accurate SBF distance measurements possible to 100 Mpc and beyond.Comment: 24 pages, 4 PostScript figures, 2 JPEG images; accepted for
publication in Ap
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
The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances
We report data for band Surface Brightness Fluctuation (SBF) magnitudes,
V-I colors, and distance moduli for 300 galaxies. The Survey contains E, S0 and
early-type spiral galaxies in the proportions of 49:42:9, and is essentially
complete for E galaxies to Hubble velocities of 2000 km/s, with a substantial
sampling of E galaxies out to 4000 km/s. The median error in distance modulus
is 0.22 mag.
We also present two new results from the Survey. (1) We compare the mean
peculiar flow velocity (bulk flow) implied by our distances with predictions of
typical cold dark matter transfer functions as a function of scale, and find
very good agreement with cold, dark matter cosmologies if the transfer function
scale parameter , and the power spectrum normalization are
related by . Derived directly from
velocities, this result is independent of the distribution of galaxies or
models for biasing. The modest bulk flow contradicts reports of large-scale,
large-amplitude flows in the Mpc diameter volume surrounding our
Survey volume. (2) We present a distance-independent measure of absolute galaxy
luminosity, \Nbar, and show how it correlates with galaxy properties such as
color and velocity dispersion, demonstrating its utility for measuring galaxy
distances through large and unknown extinction.Comment: Accepted for publication in ApJ (10 January 2001); 23 page
Measuring Distances Using Infrared Surface Brightness Fluctuations
Surface brightness fluctuations (SBFs) are much brighter in the IR than they
are at optical wavelengths, making it possible to measure greater distances
using IR SBFs. We report new K' (2.1 micron) SBF measurements of 9 galaxies in
the Fornax and Eridanus clusters using a 1024^2-pixel HgCdTe array. We used
improved analysis techniques to remove contributions from globular clusters and
background galaxies, and we assess the relative importance of other sources of
residual variance. We applied the improved methodology to Fornax and Eridanus
images and to previously published Virgo cluster data. Apparent fluctuation
magnitudes were used in conjunction with Cepheid distances to M31 and the Virgo
cluster to calibrate the K' SBF distance scale. We find the absolute
fluctuation magnitude MK'= -5.61+/-0.12, with an intrinsic scatter to the
calibration of 0.06 mag. No statistically significant change in MK' is detected
as a function of (V-I). Our calibration is consistent with constant age and
metallicity stellar population models. The lack of a correlation with (V-I) in
the context of the stellar population models implies that elliptical galaxies
bluer than (V-I)=1.2 have SBFs dominated by younger (5-8 Gyr) populations. K'
SBFs prove to be a reliable distance indicator as long as the residual variance
from globular clusters and background galaxies is properly removed. Also, it is
important that a sufficiently high S/N ratio be achieved to allow reliable sky
subtraction because residual spatial variance can bias the measurement of the
SBF power spectrum. (abridged)Comment: Accepted for publication in ApJ, 44 pages, 10 Postscript figure
Hubble Space Telescope Imaging of Lyman Alpha Emission at z=4.4
We present the highest redshift detections of resolved Lyman alpha emission,
using Hubble Space Telescope/ACS F658N narrowband-imaging data taken in
parallel with the Wide Field Camera 3 Early Release Science program in the
GOODS CDF-S. We detect Lyman alpha emission from three spectroscopically
confirmed z = 4.4 Lyman alpha emitting galaxies (LAEs), more than doubling the
sample of LAEs with resolved Lyman alpha emission. Comparing the light
distribution between the rest-frame ultraviolet continuum and narrowband
images, we investigate the escape of Lyman alpha photons at high redshift.
While our data do not support a positional offset between the Lyman alpha and
rest-frame ultraviolet (UV) continuum emission, the half-light radii in two out
of the three galaxies are significantly larger in Lyman alpha than in the
rest-frame UV continuum. This result is confirmed when comparing object sizes
in a stack of all objects in both bands. Additionally, the narrowband flux
detected with HST is significantly less than observed in similar filters from
the ground. These results together imply that the Lyman alpha emission is not
strictly confined to its indigenous star-forming regions. Rather, the Lyman
alpha emission is more extended, with the missing HST flux likely existing in a
diffuse outer halo. This suggests that the radiative transfer of Lyman alpha
photons in high-redshift LAEs is complicated, with the interstellar-medium
geometry and/or outflows playing a significant role in galaxies at these
redshifts.Comment: Submitted to the Astrophysical Journal. 11 pages, 10 figure