107 research outputs found
Detection of a spiral lens galaxy and optical variability in the gravitational lens system B1600+434
The gravitationally lensed quasar B1600+434 (z=1.61, mV=21.6) has been
observed at the 2.56m Nordic Optical Telescope (NOT). In this Letter we report
the discovery of an edge-on late-type galaxy located between the two lensed
components (separation 1\farcs4), close to the fainter image. The galaxy
photometry indicates that its redshift is approximately 0.4. We detect a large
colour difference between the two images due to significant obscuration of the
faint image. The estimated amount of absorption as a function of colour
indicates that the extinction may be due to dust in the lensing galaxy. We also
present evidence of flux variability in B1600+434 with a detected change of
0.25mag in one year. The theoretically expected time delay is of the order of
one month and so the system may be an interesting object for determining the
Hubble constant.Comment: 4 pages, 3 postscript figures, accepted for publication in A&A
Letter
Discovery of a high-redshift Einstein ring
We report the discovery of a partial Einstein ring of radius 1.48arcsec
produced by a massive (and seemingly isolated) elliptical galaxy. The
spectroscopic follow-up at the VLT reveals a 2L* galaxy at z=0.986, which is
lensing a post-starburst galaxy at z=3.773. This unique configuration yields a
very precise measure of the mass of the lens within the Einstein radius,
(8.3e11 +- 0.4)/h70 Msolar. The fundamental plane relation indicates an
evolution rate of d [log (M/L)B] / dz = -0.57+-0.04, similar to other massive
ellipticals at this redshift. The source galaxy shows strong interstellar
absorption lines indicative of large gas-phase metallicities, with fading
stellar populations after a burst. Higher resolution spectra and imaging will
allow the detailed study of an unbiased representative of the galaxy population
when the universe was just 12% of its current age.Comment: 5 pages, 3 figures, accepted in A&A Le
Spectroscopic confirmation of a cluster of galaxies at z=1 in the field of the gravitational lens MG2016+112
We present new optical data on the cluster AX J2019+1127 identified by the
X-ray satellite ASCA at z\sim 1 (Hattori et al. 1997). The data suggest the
presence of a high-redshift cluster of galaxies responsible for the large
separation triple quasar MG2016+112. Our deep photometry reveals an excess of
z\sim 1 galaxy candidates, as already suspected by Benitez et al. (1999). Our
spectroscopic survey of 44 objects in the field shows an excess of 6 red
galaxies securely identified at z \sim 1, with a mean redshift of z =1.005 +/-
0.002. We estimate a velocity dispersion of \sigma = 771 (+430/-160) km s(-1)
based on these 6 galaxies and a V-band mass-to-light ratio of 215 (+308/-77)
h_50 M/L_sol. Our observations thus confirm the existence of a massive
structure acting as the lens, which explains the unusual configuration of the
triple quasar. Hence, there is no more need to invoke the existence of a ``dark
cluster'' to understand this lens system.Comment: 8 pages, 4 figures, uses aa.cls, accepted to Astronomy and
Astrophysics with minor change
Gamma-ray burst host galaxies and the link to star-formation
We briefly review the current status of the study of long-duration gamma-ray
burst (GRB) host galaxies. GRB host galaxies are mainly interesting to study
for two reasons: 1) they may help us understand where and when massive stars
were formed throughout cosmic history, and 2) the properties of host galaxies
and the localisation within the hosts where GRBs are formed may give essential
clues to the precise nature of the progenitors. The main current problem is to
understand to what degree GRBs are biased tracers of star formation. If GRBs
are only formed by low-metallicity stars, then their host galaxies will not
give a representative view of where stars are formed in the Universe (at least
not a low redshifts). On the other hand, if there is no dependency on
metallicity then the nature of the host galaxies leads to the perhaps
surprising conclusion that most stars are formed in dwarf galaxies. In order to
resolve this issue and to fully exploit the potential of GRBs as probes of
star-forming galaxies throughout the observable universe it is mandatory that a
complete sample of bursts with redshifts and host galaxy detections is built.Comment: 9 pages, 3 figures. To appear in the proceedings of the Eleventh
Marcel Grossmann Meeting on General Relativity, eds. H. Kleinert, R. T.
Jantzen & R. Ruffini, World Scientific, Singapore, 200
Breaking the Disk/Halo Degeneracy with Gravitational Lensing
The degeneracy between the disk and the dark matter contribution to galaxy
rotation curves remains an important uncertainty in our understanding of disk
galaxies. Here we discuss a new method for breaking this degeneracy using
gravitational lensing by spiral galaxies, and apply this method to the spiral
lens B1600+434 as an example. The combined image and lens photometry
constraints allow models for B1600+434 with either a nearly singular dark
matter halo, or a halo with a sizable core. A maximum disk model is ruled out
with high confidence. Further information, such as the circular velocity of
this galaxy, will help break the degeneracies. Future studies of spiral galaxy
lenses will be able to determine the relative contribution of disk, bulge, and
halo to the mass in the inner parts of galaxies.Comment: Replaced with minor revisions, a typo fixed, and reference added; 21
pages, 8 figures, ApJ accepte
Mass and dust in the disk of a spiral lens galaxy
Gravitational lensing is a potentially important probe of spiral galaxy
structure, but only a few cases of lensing by spiral galaxies are known. We
present Hubble Space Telescope and Magellan observations of the two-image
quasar PMN J2004-1349, revealing that the lens galaxy is a spiral galaxy. One
of the quasar images passes through a spiral arm of the galaxy and suffers 3
magnitudes of V-band extinction. Using simple lens models, we show that the
mass quadrupole is well-aligned with the observed galaxy disk. A more detailed
model with components representing the bulge and disk gives a bulge-to-disk
mass ratio of 0.16 +/- 0.05. The addition of a spherical dark halo, tailored to
produce an overall flat rotation curve, does not change this conclusion.Comment: ApJ, in press [9pp, 7 figs
Gravitational lensing statistical properties in general FRW cosmologies with dark energy component(s): analytic results
Various astronomical observations have been consistently making a strong case
for the existence of a component of dark energy with negative pressure in the
universe. It is now necessary to take the dark energy component(s) into account
in gravitational lensing statistics and other cosmological tests. By using the
comoving distance we derive analytic but simple expressions for the optical
depth of multiple image, the expected value of image separation and the
probability distribution of image separation caused by an assemble of singular
isothermal spheres in general FRW cosmological models with dark energy
component(s). We also present the kinematical and dynamical properties of these
kinds of cosmological models and calculate the age of the universe and the
distance measures, which are often used in classical cosmological tests. In
some cases we are able to give formulae that are simpler than those found
elsewhere in the literature, which could make the cosmological tests for dark
energy component(s) more convenient.Comment: 14 pages, no figure, Latex fil
Keck Spectroscopy of Three Gravitational Lens Systems Discovered in the JVAS and CLASS Surveys
We present spectra of three gravitational lens systems taken with the Low
Resolution Imaging Spectrograph on the W. M. Keck Telescopes. All of the
systems were discovered in the JVAS and CLASS radio surveys, which were
designed to find lenses suitable for measuring . Previous spectra of these
systems had low signal-to-noise ratios, and only one of the source redshifts
was secure. Our observations give unambiguous lens and source redshifts for all
of the systems, with (, ) = (0.4060,1.339), (0.5990,1.535) and
(0.4144,1.589) for B0712+472, B1030+074 and B1600+434, respectively. The
observed image splittings in the systems imply that the masses of the lensing
galaxies within their Einstein rings are 5.4, 1.2, and 6.3\times 10^{10} h^{-1} M_{\sun}. The resulting V-band
mass-to-light ratios for B0712+472 and B1030+074, measured inside their
Einstein ring radii, are \sim 10h (M/L)_{\sun, V}, slightly higher than
values observed in nearby ellipticals. For B1600+434, the mass-to-light ratio
is 48h (M/L)_{\sun, V}. This high value can be explained, at least in part,
by the prominent dust lane running through the galaxy. Two of the three lens
systems show evidence of variability, so monitoring may yield a time delay and
thus a measurement of .Comment: 8 pages, 5 Postscript Figures, uses aastex. To appear in A.
The geometry of the quadruply imaged quasar PG 1115+080; implications for Ho
Time delay measurements have recently been reported for the lensed quasar PG
1115+080. These measurements can be used to derive Ho, but only if we can
constrain the lensing potential. We have applied a recently developed
deconvolution technique to analyse sub-arcsecond I band images of PG 1115+080,
obtained at the Nordic Optical Telescope (NOT) and the Canada France Hawaii
Telescope (CFHT). The high performance of the deconvolution code allows us to
derive precise positions and magnitudes for the four lensed images of the
quasar, as well as for the lensing galaxy. The new measurement of the galaxy
position improves its precision by a factor of 3 and thus strengthens the
constraints on the lensing potential. With the new data, a range of models
incorporating some of the plausible systematic uncertainties yields Ho = 53
(+10/-7) km/s/mpc.Comment: 4 pages, LaTex file + postscript figures, Accepted for publication in
AA Letter
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