19 research outputs found
Constraints on Galaxy Density Profiles from Strong Gravitational Lensing: The Case of B 1933+503
We consider a wide range of parametric mass models for B 1933+503, a
ten-image radio lens, and identify shared properties of the models with the
best fits. The approximate rotation curves varies by less than 8.5% from the
average value between the innermost and the outermost image (1.5h^{-1} kpc to
4.1h^{-1} kpc) for models within 1 \sigma of the best fit, and the radial
dependence of the shear strength and angle also have common behavior for the
best models. The time delay between images 1 and 6, the longest delay between
the radio cores, is \Delta t = (10.6^{+2.4}_{-1.1})h^{-1} days (\Omega_0=0.3,
\lambda_0=0.7) including all the modeling uncertainties. Deeper infrared
observations, to more precisely register the lens galaxy with the radio images
and to measure the properties of the Einstein ring image of the radio source's
host galaxy, would significantly improve the model constraints and further
reduce the uncertainties in the mass distribution and time delay.Comment: 24 pages, 10 figures, final version to appear in ApJ. Some minor
corrections (e.g. constraint on central unseen image was stronger than
intended earlier, now agrees with text, conventions on angles fixed in
text/plots). Resulting model fits have some change in chi squareds and best
parameters (e.g. cores, flatness of rotation curve) have some changes.
Properties of model families and trends for best fitting models very close to
earlier results; general conclusions the sam
Limits on a Stochastic Background of Gravitational Waves from Gravitational Lensing
We compute the effects of a stochastic background of gravitational waves on
multiply imaged systems or on weak lensing. There are two possible observable
effects, a static relative deflection of images or shear, and an induced time
dependent shift or proper motion. We evaluate the rms magnitude of these
effects for a COBE normalized, scale-invariant spectrum, which is an upper
limit on spectra produced by inflation. Previous work has shown that
large-scale structure may cause a relative deflection large enough to affect
observations, but we find that the corresponding effect of gravity waves is
smaller by and so cannot be observed. This results from the
oscillation in time as well as the redshifting of the amplitude of gravity
waves. We estimate the magnitude of the proper motion induced by deflection of
light due to large-scale structure, and find it to be arcsec per
year. This corresponds to km/s at cosmological distances, which is
quite small compared to typical peculiar velocities. The COBE normalized
gravity wave spectrum produces motions smaller still by . We
conclude that light deflection due to these cosmological perturbations cannot
produce observable proper motions of lensed images. On the other hand, there
are only a few known observational limits on a stochastic background of gravity
waves at shorter, astrophysical wavelengths. We calculate the expected
magnitudes of the effects of lensing by gravity waves of such wavelengths, and
find that they are too small to yield interesting limits on the energy density
of gravity waves.Comment: 14 pages, LaTex + 1 PS Figure, accepted version to be published in
Phys. Rev. D15, Dec. 1996. An incorrect assumption was removed, also various
other minor change
Gravitational lensing on the Cosmic Microwave Background by gravity waves
We study the effect of a stochastic background of gravitational waves on the
gravitational lensing of the Cosmic Microwave Background (CMB) radiation. It
has been shown that matter density inhomogeneities produce a smoothing of the
acoustic peaks in the angular power spectrum of the CMB anisotropies. A
gravitational wave background gives rise to an additional smoothing of the
spectrum. For the most simple case of a gravitational wave background arising
during a period of inflation, the effect results to be three to four orders of
magnitude smaller than its scalar counterpart, and is thus undetectable. It
could play a more relevant role in models where a larger background of
gravitational waves is produced.Comment: 6 pages, RevTeX file, 1 figur
The impact of lens galaxy environments on the image separation distribution
We study the impact of lens galaxy environments on the image separation
distribution of lensed quasars. We account for both environmental convergence
and shear, using a joint distribution derived from galaxy formation models
calibrated by galaxy-galaxy lensing data and number counts of massive
elliptical galaxies. We find that the external field enhances lensing
probabilities, particularly at large image separations; the increase is ~30% at
\theta=3'' and ~200% at \theta=5'', when we adopt a power-law source luminosity
function \Phi(L) \propto L^-2.1. The enhancement is mainly driven by
convergence, which boosts both the image separation and magnification bias (for
a fixed lens galaxy mass). These effects have been neglected in previous
studies of lens statistics. Turning the problem around, we derive the posterior
convergence and shear distributions and point out that they are strong
functions of image separation; lens systems with larger image separations are
more likely to lie in dense environments.Comment: 8 pages, 10 figures, accepted for publication in MNRA
Determination of Inflationary Observables by Cosmic Microwave Background Anisotropy Experiments
Inflation produces nearly Harrison-Zel'dovich scalar and tensor perturbation
spectra which lead to anisotropy in the cosmic microwave background (CMB). The
amplitudes and shapes of these spectra can be parametrized by , , and where and are the scalar and
tensor contributions to the square of the CMB quadrupole and and
are the power-lawspectral indices. Even if we restrict ourselves to information
from angles greater than one third of a degree, three of these observables can
be measured with some precision. The combination can be
known to better than . The scalar index can be determined to
better than . The ratio can be known to about for and slightly better for smaller . The precision with which
can be measured depends weakly on and strongly on . For
can be determined with a precision of about . A
full-sky experiment with a beam using technology available today, similar
to those being planned by several groups, can achieve the above precision. Good
angular resolution is more important than high signal-to-noise ratio; for a
given detector sensitivity and observing time a smaller beam provides
significantly more information than a larger beam. The uncertainties in
and are roughly proportional to the beam size. We briefly discuss the
effects of uncertainty in the Hubble constant, baryon density, cosmological
constant and ionization history.Comment: 28 pages of uuencoded postscript with 8 included figures. A
postscript version is also available by anonymous ftp at
ftp://astro.uchicago.edu/pub/astro/knox/fullsim.p
Reconstructing the Inflaton Potential --- an Overview
We review the relation between the inflationary potential and the spectra of
density (scalar) perturbations and gravitational waves (tensor perturbations)
produced, with particular emphasis on the possibility of reconstructing the
inflaton potential from observations. The spectra provide a potentially
powerful test of the inflationary hypothesis; they are not independent but
instead are linked by consistency relations reflecting their origin from a
single inflationary potential. To lowest-order in a perturbation expansion
there is a single, now familiar, relation between the tensor spectral index and
the relative amplitude of the spectra. We demonstrate that there is an infinite
hierarchy of such consistency equations, though observational difficulties
suggest only the first is ever likely to be useful. We also note that since
observations are expected to yield much better information on the scalars than
on the tensors, it is likely to be the next-order version of this consistency
equation which will be appropriate, not the lowest-order one. If inflation
passes the consistency test, one can then confidently use the remaining
observational information to constrain the inflationary potential, and we
survey the general perturbative scheme for carrying out this procedure.
Explicit expressions valid to next-lowest order in the expansion are presented.
We then briefly assess the prospects for future observations reaching the
quality required, and consider a simulated data set that is motivated by this
outlook.Comment: 69 pages standard LaTeX plus 4 postscript figures. Postscript version
of text in landscape format (35 pages) available at
http://star-www.maps.susx.ac.uk/papers/infcos_papers.html Modifications are a
variety of updates to discussion and reference