276 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
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 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
A Photometric Investigation of the GRB970228 Afterglow and the Associated Nebulosity
We carefully analyze the WFPC2 and STIS images of GRB970228. We measure
magnitudes for the GRB970228 point source component in the WFPC2 images of
, and
, on March 26 and April 7,
respectively; and on September 4 in the STIS image.
For the extended component, we measure magnitudes of
in the combined WFPC2 images and
in the STIS image, which are consistent with no
variation. This value is fainter than previously reported (Galama et al. 98)
and modifies the previously assumed magnitudes for the optical transient when
it faded to a level where the extended source component contribution was not
negligible, alleviating the discrepancy to a power-law temporal behavior. We
also measure a color of for the
extended source component. Taking into account the extinction measured in this
field (Castander & Lamb 1998), this color implies that the extended source is
most likely a galaxy with ongoing star formation.Comment: 21 pages, including 8 figures. Submitted to Ap
The Extinction Towards the GRB970228 Field
We determine the local galactic extinction towards the field of gamma-ray
burst GRB970228 using a variety of methods. We develop a maximum likelihood
method for measuring the extinction by comparing galaxy counts in the field of
interest to those in a field of known extinction, and apply this method to the
GRB970228 field. We also measure the extinction by comparing the observed
stellar spectral energy distributions of stars in the GRB970228 field to the
spectral energy distribution of library spectra of the same spectral type.
Finally we estimate the extinction using the Balmer emission line ratios of a
galaxy in the GRB970228 field, and the neutral hydrogen column density and
amount of infrared dust emission toward this field. Combining the results of
these methods, we find a best-fit galactic extinction in the optical of
, which implies a a substantial dimming and change of
the spectral slope of the intrinsic GRB970228 afterglow.Comment: 22 pages, including 7 figures. Submitted to Ap
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