525 research outputs found
The GL bibliography and an interactive database
It is now possible to directly access, via the Internet, a bibliographical
database on Gravitational Lensing (GL) literature. The Interactive
Gravitational Lensing Bibliography (IGLB) totalizes more than 2400 titles of
published articles in scientific journals and meeting proceedings (except those
fully dedicated to Gravitational Lenses) as well as papers submitted to the
e-Print archive. This database is a product from the Gravitational Lensing
Bibliography first presented in 1993 (Proceedings of the 31st Liege
International Astrophysical Colloquium). It is easy to do field based searches
for title keywords, authors (using boolean operators), year and journal (a
pull-down list of the most cited journals is available). Access to the original
version of published articles as well as to preprints submitted to the e-Print
archive at the URL address http://xxx.lanl.gov/ is also provided. This database
is updated approximately every two months. The "complete" bibliography of
published articles is also available in the form of Latex and PostScript files.
The IGLB can be accessed at the URL: http://vela.astro.ulg.ac.be/grav_lensComment: 2 pages, 2 figures, uses paspconf.sty. Poster contribution to
"Gravitational Lensing: Recent Progress and Future Goals", Boston University
1999, eds. T. G. Brainerd and C. S. Kochane
Redshift estimate of a gravitational lens from the observed reddening of a multiply imaged quasar
Light rays from a multiply imaged quasar usually sample different path
lengths across the deflector. Extinction in the lensing galaxy may thus lead to
a differential obscuration and reddening between the observed macro-lensed QSO
images. These effects naturally depend on the precise shape of the extinction
law and on the redshift of the lens. By means of numerical Monte-Carlo
simulations, using a least-squares fitting method and assuming an extinction
law similar to that observed in the Galaxy, we show how accurate photometric
observations of multiply imaged quasars obtained in several spectral bands
could lead to the estimate of the lens redshift, irrespective of the visibility
of the deflector. Observational requirements necessary to apply this method to
real cases are thoroughly discussed. If extinction laws turn out to be too
different from galaxy to galaxy, we find out that more promising observations
should consist in getting high signal-to-noise low resolution spectra of at
least three distinct images of a lensed quasar, over a spectral range as wide
as possible, from which it should be straightforward to extract the precise
shape of the redshifted extinction law. Very high signal-to-noise, low spectral
resolution, VLT observations of H1413+117 and MG 0414+0534 should enable one to
derive such a redshifted extinction law.Comment: 7 pages, 11 figures, to appear in Astronomy and Astrophysics (also
available at http://vela.astro.ulg.ac.be/preprint/
Search for gravitational lens candidates in the XMM-LSS/CFHTLS common field
Our aim was to identify gravitational lens candidates among some 5500 optical
counterparts of the X-ray point-like sources in the medium-deep ~11 sq. deg.
XMM-LSS survey. We have visually inspected the optical counterparts of each
QSOs/AGN using CFHTLS T006 images. We have selected compact pairs and groups of
sources which could be multiply imaged QSO/AGN. We have measured the colors and
characterized the morphological types of the selected sources using the
multiple PSF fitting technique. We found three good gravitational lens
candidates: J021511.4-034306, J022234.3-031616 and J022607.0-040301 which
consist of pairs of point-like sources having similar colors. On the basis of a
color-color diagram and X-ray properties we could verify that all these sources
are good QSO/AGN candidates rather than stars. Additional secondary
gravitational lens candidates are also reported.Comment: 6 pages, 3 figures, 1 table, Accepted for publication in MNRA
2MASS Reveals a Large Intrinsic Fraction of BALQSOs
The intrinsic fraction of broad absorption line quasars (BALQSOs) is
important in constraining geometric and evolutionary models of quasars. We
present the fraction of BALQSOs in 2MASS detected quasars within the SDSS DR3
sample in the redshift range of 1.7 < z < 4.38. The fraction of BALQSOs is
40.4^{+3.4}_{-3.3}% in the 2MASS 99% database K_s band completeness sample, and
38.5^{+1.7}_{-1.7}% in the larger 2MASS sample extending below the completeness
limit. These fractions are significantly higher than the 26% reported in the
optical bands for the same parent sample. We also present the fraction of
BALQSOs as functions of apparent magnitudes, absolute magnitudes, and redshift
in the 2MASS and SDSS bands. The 2MASS fractions are consistently higher than
the SDSS fractions in every comparison, and the BALQSO fractions steadily
increase with wavelength from the SDSS u to the 2MASS K_s bands. Furthermore,
the i - K_s color distributions of BALQSOs and non-BALQSOs indicate that
BALQSOs are redder than non-BALQSOs, with a K-S test probability of 2e-12.
These results are consistent with the spectral difference between BALQSOs and
non-BALQSOs including both the absorption troughs and dust extinction in
BALQSOs, which leads to significant selection biases against BALQSOs in the
optical bands. Using a simple simulation incorporating the luminosity function
of quasars and the amount of obscuration for BALQSOs, we simultaneously fit the
BALQSO fractions in the SDSS and 2MASS bands. We obtain a true BALQSO fraction
of 43\pm2% for luminous quasars (M_{K_s} \lesssim -30.1 mag).Comment: 20 pages, 6 figures, accepted by Ap
The Butcher--Oemler effect at z~0.35: a change in perspective
The present paper focuses on the much debated Butcher-Oemler effect: the
increase with redshift of the fraction of blue galaxies in clusters.
Considering a representative cluster sample made of seven group/clusters at
z~0.35, we have measured the blue fraction from the cluster core to the cluster
outskirts and the field mainly using wide field CTIO images. This sample
represents a random selection of a volume complete x-ray selected cluster
sample, selected so that there is no physical connection with the studied
quantity (blue fraction), to minimize observational biases. In order to
statistically assess the significance of the Butcher-Oemler effect, we
introduce the tools of Bayesian inference. Furthermore, we modified the blue
fraction definition in order to take into account the reduced age of the
universe at higher redshifts, because we should no longer attempt to reject an
unphysical universe in which the age of the Universe does depend on redshift,
whereas the age of its content does not. We measured the blue fraction from the
cluster center to the field and we find that the cluster affects the properties
of the galaxies up to two virial radii at z~0.35. Data suggest that during the
last 3 Gyrs no evolution of the blue fraction, from the cluster core to the
field value, is seen beyond the one needed to account for the varying age with
redshift of the Universe and of its content. The agreement of the radial
profiles of the blue fraction at z=0 and z~0.35 implies that the pattern infall
did not change over the last 3 Gyr, or, at least, its variation has no
observational effect on the studied quantity.Comment: MNRAS, in pres
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