18 research outputs found
A Keck Survey of Gravitational Lens Systems: I. Spectroscopy of SBS 0909+532, HST 1411+5211, and CLASS B2319+051
We present new results from a continuing Keck program to study gravitational
lens systems. We have obtained redshifts for three lens systems, SBS 0909+532,
HST 1411+5211, and CLASS B2319+051. For all of these systems, either the source
or lens redshift (or both) has been previously unidentified. We find (z_l, z_s)
= (0.830, 1.377) for SBS 0909+532; (z_l, z_s) = (0.465, 2.811) for HST
1411+5211, although the source redshift is still tentative; and (z_l1, z_l2) =
(0.624, 0.588) for the two lensing galaxies in CLASS B2319+051. The background
radio source in B2319+051 has not been detected optically; its redshift is,
therefore, still unknown. We find that the spectral features of the central
lensing galaxy in all three systems are typical of an early-type galaxy. The
observed image splittings in SBS 0909+532 and HST 1411+5211 imply that the
masses within the Einstein ring radii of the lensing galaxies are 1.4 x 10^{11}
and 2.0 x 10^{11} h^{-1} M_sun, respectively. The resulting B band
mass-to-light ratio for HST 1411+5211 is 41.3 +/- 1.2 h (M/L)_sun, a factor of
5 times higher than the average early-type lensing galaxy. This large
mass-to-light is almost certainly the result of the additional mass
contribution from the cluster CL 3C295 at z = 0.46. For the lensing galaxy in
SBS 0909+532, we measure (M/L)_B = 4^{+11}_{-3} h (M/L)_sun where the large
errors are the result of significant uncertainty in the galaxy luminosity.
While we cannot measure directly the mass-to-light ratio of the lensing galaxy
in B2319+051, we estimate that (M/L)_B is between 3-7 h (M/L)_sun.Comment: Accepted for publication in Astronomical Journal. 21 pages, including
7 figure
High resolution observations and mass modelling of the CLASS gravitational lens B1152+199
We present a series of high resolution radio and optical observations of the
CLASS gravitational lens system B1152+199 obtained with the Multi-Element
Radio-Linked Interferometer Network (MERLIN), Very Long Baseline Array (VLBA)
and Hubble Space Telescope (HST). Based on the milliarcsecond-scale
substructure of the lensed radio components and precise optical astrometry for
the lensing galaxy, we construct models for the system and place constraints on
the galaxy mass profile. For a single galaxy model with surface mass density
Sigma(r) propto r^-beta, we find that 0.95 < beta < 1.21 at 2-sigma confidence.
Including a second deflector to represent a possible satellite galaxy of the
primary lens leads to slightly steeper mass profiles.Comment: 7 pages, post-referee revision for MNRA
Optical monitoring of the gravitationally lensed quasar Q2237+0305 from APO between June 1995 and January 1998
We present a data set of images of the gravitationally lensed quasar
Q2237+0305, that was obtained at the Apache Point Observatory (APO) between
June 1995 and January 1998. Although the images were taken under variable,
often poor seeing conditions and with coarse pixel sampling, photometry is
possible for the two brighter quasar images A and B with the help of exact
quasar image positions from HST observations. We obtain a light curve with 73
data points for each of the images A and B. There is evidence for a long (>~
100 day) brightness peak in image A in 1996 with an amplitude of about 0.4 to
0.5 mag (relative to 1995), which indicates that microlensing has been taking
place in the lensing galaxy. Image B does not vary much over the course of the
observation period. The long, smooth variation of the light curve is similar to
the results from the OGLE monitoring of the system (Wozniak et al. 2000a).Comment: 8 pages, 5 figures; accepted for publication in A&
A Robust Determination of the Time Delay in 0957+561A,B and a Measurement of the Global Value of Hubble's Constant
Photometric monitoring of the gravitational lens system 0957+561A,B in the g
and r bands with the Apache Point Observatory (APO) 3.5 m telescope during 1996
shows a sharp g band event in the trailing (B) image light curve at the precise
time predicted from the observation of an event during 1995 in the leading (A)
image with a delay of 415 days. This success confirms the "short delay," and
the lack of any feature at a delay near 540 days rejects the "long delay" for
this system, resolving a long-standing controversy. A series of statistical
analyses of our light curve data yield a best fit delay of 417 +/- 3 days (95%
confidence interval). Recent improvements in the modeling of the lens system
(consisting of a galaxy and cluster) allow us to derive a value of the global
(at z = 0.36) value of Hubble's constant H_0 using Refsdal's method, a simple
and direct distance determination based on securely understood physics and
geometry. The result is H_0 = 63 +/- 12 km/s/Mpc (for Omega = 1) where this 95%
confidence interval is dominated by remaining lens model uncertainties.Comment: accepted by ApJ, AASTeX 4.0 preprint, 4 PostScript figure
Cosmological distance indicators
We review three distance measurement techniques beyond the local universe:
(1) gravitational lens time delays, (2) baryon acoustic oscillation (BAO), and
(3) HI intensity mapping. We describe the principles and theory behind each
method, the ingredients needed for measuring such distances, the current
observational results, and future prospects. Time delays from strongly lensed
quasars currently provide constraints on with < 4% uncertainty, and with
1% within reach from ongoing surveys and efforts. Recent exciting discoveries
of strongly lensed supernovae hold great promise for time-delay cosmography.
BAO features have been detected in redshift surveys up to z <~ 0.8 with
galaxies and z ~ 2 with Ly- forest, providing precise distance
measurements and with < 2% uncertainty in flat CDM. Future BAO
surveys will probe the distance scale with percent-level precision. HI
intensity mapping has great potential to map BAO distances at z ~ 0.8 and
beyond with precisions of a few percent. The next years ahead will be exciting
as various cosmological probes reach 1% uncertainty in determining , to
assess the current tension in measurements that could indicate new
physics.Comment: Review article accepted for publication in Space Science Reviews
(Springer), 45 pages, 10 figures. Chapter of a special collection resulting
from the May 2016 ISSI-BJ workshop on Astronomical Distance Determination in
the Space Ag
Gravitational Lensing in Astronomy
Deflection of light by gravity was predicted by General Relativity and
observationaly confirmed in 1919. In the following decades various aspects of
the gravitational lens effect were explored theoretically, among them the
possibility of multiple or ring-like images of background sources, the use of
lensing as a gravitational telescope on very faint and distant objects, and the
possibility to determine Hubble's constant with lensing. Only relatively
recently gravitational lensing became an observational science after the
discovery of the first doubly imaged quasar in 1979. Today lensing is a booming
part of astrophysics.
In addition to multiply-imaged quasars, a number of other aspects of lensing
have been discovered since, e.g. giant luminous arcs, quasar microlensing,
Einstein rings, galactic microlensing events, arclets, or weak gravitational
lensing. By now literally hundreds of individual gravitational lens phenomena
are known.
Although still in its childhood, lensing has established itself as a very
useful astrophysical tool with some remarkable successes. It has contributed
significant new results in areas as different as the cosmological distance
scale, the large scale matter distribution in the universe, mass and mass
distribution of galaxy clusters, physics of quasars, dark matter in galaxy
halos, or galaxy structure.Comment: Review article for "Living Reviews in Relativity", see
http://www.livingreviews.org . 41 pages, latex, 22 figures (partly in GIF
format due to size constraints). High quality postscript files can be
obtained electronically at http://www.aip.de:8080/~jkw/review_figures.htm
Class B1555+375: A new four-image gravitational lens system
We have discovered a new gravitational lens in the Cosmic Lens All-Sky Survey. The lens B1555 + 375 is a four-image system with a maximum separation of 0." 42. VLA and MERLIN radio observations show these images in a characteristic quadruple-lens configuration. Optical imaging with the Keck II Telescope at R band shows a faint extended object. We estimate the combined emission from the lens and background source to be R = 25 mag. Observations at H band with the William Herschel Telescope also detected this extended object. The combined lens and background source magnitude was measured to be H = 19 mag. Presently, redshifts for both the lensing galaxy and background source are undetermined. We conclude that one or more of the following are true: the lens galaxy is sub-L*, it has z > 0.5, or it is highly reddened. The observed MERLIN component positions and flux densities can be well described by a lens model based on a singular isothermal ellipsoid mass distribution. Our best-fit lens model has a reduced chi(2) Of 2.6. High-resolution VLA radio observations should help to constrain the lens model further