296 research outputs found
Cross-correlating the Microwave Sky with Galaxy Surveys
We present results for the cross-correlation between the WMAP 1st-year cosmic
microwave background (CMB) anisotropy data and optical galaxy surveys: the APM
and SDSS DR1 catalogs. Our measurement of a positive CMB-galaxy correlation on
large angles (\theta > 4 deg) yields significant detections of the Integrated
Sachs-Wolfe (ISW) effect and provides a new estimate of dark-energy in the
universe, \Omega_\Lambda=0.69-0.86 (2 \sigma range). In addition, the
correlated signal on small angles (\theta<1 deg) reveals the imprint left by
hot intra-cluster gas in the CMB photons: the thermal Sunyaev-Zeldovich (SZ)
effectComment: 7 pages. Invited talk at XVth Rencontres de Blois (France): "Physical
Cosmology", June 2003. References adde
The GRB/SN Connection: An Improved Spectral Flux Distribution for the Supernova Candidate Associated with GRB 970228
We better determine the spectral flux distribution of the supernova candidate
associated with GRB 970228 by modeling the spectral flux distribution of the
host galaxy of this burst, fitting this model to measurements of the host
galaxy, and using the fitted model to better subtract out the contribution of
the host galaxy to measurements of the afterglow of this burst.Comment: To appear in Proc. of the 10th Annual October Astrophysics Conference
in Maryland: Cosmic Explosions, 4 pages, LaTe
The GRB/SN Connection: An Improved Spectral Flux Distribution for the SN-Like Component to the Afterglow of GRB 970228, the Non-Detection of a SN-Like Component to the Afterglow of GRB 990510, and GRBs as Beacons to Locate SNe at Redshifts z = 4 - 5
We better determine the spectral flux distribution of the supernova candidate
associated with GRB 970228 by modeling the spectral flux distribution of the
host galaxy of this burst, fitting this model to measurements of the host
galaxy, and using the fitted model to better subtract out the contribution of
the host galaxy to measurements of the afterglow of this burst. Furthermore, we
discuss why the non-detection of a SN1998bw-like component to the afterglow of
GRB 990510 does not necessarily imply that a SN is not associated with this
burst. Finally, we discuss how bursts can be used as beacons to locate SNe out
to redshifts of z = 4 - 5.Comment: To appear in Proc. of the 5th Huntsville Gamma-Ray Burst Symposium, 5
pages, LaTe
Detection of the ISW and SZ effects from the CMB-Galaxy correlation
We present a cross-correlation analysis of the WMAP cosmic microwave
background (CMB) temperature anisotropies and the SDSS galaxy density
fluctuations. We find significant detections of the angular CMB-galaxy
correlation for both the flux limited galaxy sample (z~0.3) and the high
redshift (z ~ 0.5) color selected sample. The signal is compatible with that
expected from the integrated Sachs-Wolfe (ISW) effect at large angles (\theta >
3deg) and the Sunyaev-Zeldovich (SZ) effect at small scales (\theta < 1 deg).
The detected correlation at low-z is in good agreement with a previous analysis
using the APM survey (z~0.15). The combined analysis of all 3 samples yields a
total significance better than 3 sigma for ISW and about 2.7 \sigma for SZ,
with a Compton parameter y~10^(-6). For a given flat LCDM model, the ISW effect
depends both on the value of \Omega_\Lambda and the galaxy bias b. To break
this degeneracy, we estimate the bias using the ratio between the galaxy and
mass auto-correlation functions in each sample. With our bias estimation, all
samples consistently favor a best fit dark-energy dominated model:
\Omega_\Lambda ~ 0.8, with a 2 \sigma error \Omega_\Lambda=0.69-0.86.Comment: Accepted by ApJL. New figure and further discussion about error
estimate
Missing Lensed Images and the Galaxy Disk Mass in CXOCY J220132.8-320144
The CXOCY J220132.8-320144 system consists of an edge-on spiral galaxy
lensing a background quasar into two bright images. Previous efforts to
constrain the mass distribution in the galaxy have suggested that at least one
additional image must be present (Castander et al. 2006). These extra images
may be hidden behind the disk which features a prominent dust lane. We present
and analyze Hubble Space Telescope (HST) observations of the system. We do not
detect any extra images, but the observations further narrow the observable
parameters of the lens system. We explore a range of models to describe the
mass distribution in the system and find that a variety of acceptable model
fits exist. All plausible models require 2 magnitudes of dust extinction in
order to obscure extra images from detection, and some models may require an
offset between the center of the galaxy and the center of the dark matter halo
of 1 kiloparsec. Currently unobserved images will be detectable by future James
Webb Space Telescope (JWST) observations and will provide strict constraints on
the fraction of mass in the disk.Comment: 10 pages, 8 figures, 6 tables. Minor changes, version accepted for
publication in Ap
Measuring the growth of matter fluctuations with third-order galaxy correlations
Measurements of the linear growth factor at different redshifts are
key to distinguish among cosmological models. One can estimate the derivative
from redshift space measurements of the 3D anisotropic galaxy
two-point correlation , but the degeneracy of its transverse (or
projected) component with galaxy bias , i.e. , introduces large errors in the growth measurement. Here we present a
comparison between two methods which break this degeneracy by combining second-
and third-order statistics. One uses the shape of the reduced three-point
correlation and the other a combination of third-order one- and two-point
cumulants. These methods use the fact that, for Gaussian initial conditions and
scales larger than Mpc, the reduced third-order matter
correlations are independent of redshift (and therefore of the growth factor)
while the third-order galaxy correlations depend on . We use matter and halo
catalogs from the MICE-GC simulation to test how well we can recover and
therefore with these methods in 3D real space. We also present a new
approach, which enables us to measure directly from the redshift evolution
of second- and third-order galaxy correlations without the need of modelling
matter correlations. For haloes with masses lower than
M, we find deviations between the different estimates of
, which are comparable to current observational errors. At higher masses we
find larger differences that can probably be attributed to the breakdown of the
bias model and non-Poissonian shot noise.Comment: 24 pages, 20 figures, 2 tables, accepted for publication in MNRA
The Complete Calibration of the Color-Redshift Relation (C3R2) Survey: Survey Overview and Data Release 1
A key goal of the Stage IV dark energy experiments Euclid, LSST and WFIRST is
to measure the growth of structure with cosmic time from weak lensing analysis
over large regions of the sky. Weak lensing cosmology will be challenging: in
addition to highly accurate galaxy shape measurements, statistically robust and
accurate photometric redshift (photo-z) estimates for billions of faint
galaxies will be needed in order to reconstruct the three-dimensional matter
distribution. Here we present an overview of and initial results from the
Complete Calibration of the Color-Redshift Relation (C3R2) survey, designed
specifically to calibrate the empirical galaxy color-redshift relation to the
Euclid depth. These redshifts will also be important for the calibrations of
LSST and WFIRST. The C3R2 survey is obtaining multiplexed observations with
Keck (DEIMOS, LRIS, and MOSFIRE), the Gran Telescopio Canarias (GTC; OSIRIS),
and the Very Large Telescope (VLT; FORS2 and KMOS) of a targeted sample of
galaxies most important for the redshift calibration. We focus spectroscopic
efforts on under-sampled regions of galaxy color space identified in previous
work in order to minimize the number of spectroscopic redshifts needed to map
the color-redshift relation to the required accuracy. Here we present the C3R2
survey strategy and initial results, including the 1283 high confidence
redshifts obtained in the 2016A semester and released as Data Release 1.Comment: Accepted to ApJ. 11 pages, 5 figures. Redshifts can be found at
http://c3r2.ipac.caltech.edu/c3r2_DR1_mrt.tx
The Evolution of Luminous Compact Blue Galaxies: Disks or Spheroids?
Luminous compact blue galaxies (LCBGs) are a diverse class of galaxies
characterized by high luminosity, blue color, and high surface brightness that
sit at the critical juncture of galaxies evolving from the blue to the red
sequence. As part of our multi-wavelength survey of local LCBGs, we have been
studying the HI content of these galaxies using both single-dish telescopes and
interferometers. Our goals are to determine if single-dish HI observations
represent a true measure of the dynamical mass of LCBGs and to look for
signatures of recent interactions that may be triggering star formation in
LCBGs. Our data show that while some LCBGs are undergoing interactions, many
appear isolated. While all LCBGs contain HI and show signatures of rotation,
the population does not lie on the Tully-Fisher relation nor can it evolve onto
it. Furthermore, the HI maps of many LCBGs show signatures of dynamically hot
components, suggesting that we are seeing the formation of a thick disk or
spheroid in at least some LCBGs. There is good agreement between the HI and
H-alpha kinematics for LCBGs, and both are similar in appearance to the H-alpha
kinematics of high redshift star-forming galaxies. Our combined data suggest
that star formation in LCBGs is primarily quenched by virial heating,
consistent with model predictions.Comment: 4 pages, 2 figures, to appear in the proceedings of IAU Symposium
277, "Tracing the Ancestry of Galaxies on the Land of our Ancestors", eds. C.
Carignan, K.C. Freeman, and F. Combe
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