1,712 research outputs found
Gravitational Lensing Limits on the Average Redshift of Submillimeter Sources
The submillimeter universe has now been explored with the Submillimeter
Common User Bolometer Array (SCUBA) camera on the James Clerk Maxwell
Telescope, and a claim has been made to the presence of a new population of
optically unidentified starforming galaxies at high redshifts (z \gtrsim 3).
Such a population dramatically alters current views on the star formation
history of the universe as well as galaxy formation and evolution. Recently,
new radio identifications of the Hubble Deep Field submm sources have led to
the suggestion that some of these sources are at low redshifts, however, submm
source redshift distribution is still not well determined. Here, we present an
upper limit to the average redshift by comparing the expected number of
gravitationally lensed submm sources due to foreground cluster potentials to
current observed statistics of such lensed sources. The upper limit depends on
the cosmological parameters, and at the 68% confidence level, < 3.1, 4.8,
5.2, or 8.0 for (Omega,Lambda) values of (0.3,0.7), (0.5,0.5), (0.3,0.0) or
(1.0,0.0) respectively. These upper limits are consistent with redshift
distribution for 850 micron sources implied by starformation history models
based on measured background radiation at far-infrared and submm wavelengths.Comment: Accepted for publication in ApJ Letters (4 pages, including 1 table
Gravitational Lensing as a Probe of Quintessence
A large number of cosmological studies now suggest that roughly two-thirds of
the critical energy density of the Universe exists in a component with negative
pressure. If the equation of state of such an energy component varies with
time, it should in principle be possible to identify such a variation using
cosmological probes over a wide range in redshift. Proper detection of any time
variation, however, requires cosmological probes beyond the currently studied
range in redshift of 0.1 to 1. We extend our analysis to gravitational
lensing statistics at high redshift and suggest that a reliable sample of
lensed sources, out to a redshift of 5, can be used to constrain the
variation of the equation of state, provided that both the redshift
distribution of lensed sources and the selection function involved with the
lensed source discovery process are known. An exciting opportunity to catalog
an adequate sample of lensed sources (quasars) to probe quintessence is now
available with the ongoing Sloan Digital Sky Survey. Writing , we study the expected accuracy to which the equation of state
today and its rate of change can simultaneously be
constrained. Such a determination can rule out some missing-energy candidates,
such as classes of quintessence models or a cosmological constant.Comment: Accepted for publication in ApJ Letters (4 pages, including 4
figures
An Upper Limit on Omega_matter Using Lensed Arcs
We use current observations on the number statistics of gravitationally
lensed optical arcs towards galaxy clusters to derive an upper limit on the
cosmological mass density of the Universe. The gravitational lensing statistics
due to foreground clusters combine properties of both cluster evolution, which
is sensitive to the matter density, and volume change, which is sensitive to
the cosmological constant. The uncertainties associated with the predicted
number of lensing events, however, currently do not allow one to distinguish
between flat and open cosmological models with and without a cosmological
constant. Still, after accounting for known errors, and assuming that clusters
in general have dark matter core radii of the order ~ 35 h^-1 kpc, we find that
the cosmological mass density, Omega_m, is less than 0.56 at the 95%
confidence. Such a dark matter core radius is consistent with cluster
potentials determined recently by detailed numerical inversions of strong and
weak lensing imaging data. If no core radius is present, the upper limit on
Omega_m increases to 0.62 (95% confidence level). The estimated upper limit on
Omega_m is consistent with various cosmological probes that suggest a low
matter density for the Universe.Comment: 6 pages, 3 figures. Accepted version (ApJ in press
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