43 research outputs found
COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses VII. Time delays and the Hubble constant from WFI J2033-4723
Gravitationally lensed quasars can be used to map the mass distribution in
lensing galaxies and to estimate the Hubble constant H0 by measuring the time
delays between the quasar images. Here we report the measurement of two
independent time delays in the quadruply imaged quasar WFI J2033-4723 (z =
1.66). Our data consist of R-band images obtained with the Swiss 1.2 m EULER
telescope located at La Silla and with the 1.3 m SMARTS telescope located at
Cerro Tololo. The light curves have 218 independent epochs spanning 3 full
years of monitoring between March 2004 and May 2007, with a mean temporal
sampling of one observation every 4th day. We measure the time delays using
three different techniques, and we obtain Dt(B-A) = 35.5 +- 1.4 days (3.8%) and
Dt(B-C) = 62.6 +4.1/-2.3 days (+6.5%/-3.7%), where A is a composite of the
close, merging image pair. After correcting for the time delays, we find R-band
flux ratios of F_A/F_B = 2.88 +- 0.04, F_A/F_C = 3.38 +- 0.06, and F_A1/F_A2 =
1.37 +- 0.05 with no evidence for microlensing variability over a time scale of
three years. However, these flux ratios do not agree with those measured in the
quasar emission lines, suggesting that longer term microlensing is present. Our
estimate of H0 agrees with the concordance value: non-parametric modeling of
the lensing galaxy predicts H0 = 67 +13/-10 km s-1 Mpc-1, while the Single
Isothermal Sphere model yields H0 = 63 +7/-3 km s-1 Mpc-1 (68% confidence
level). More complex lens models using a composite de Vaucouleurs plus NFW
galaxy mass profile show twisting of the mass isocontours in the lensing
galaxy, as do the non-parametric models. As all models also require a
significant external shear, this suggests that the lens is a member of the
group of galaxies seen in field of view of WFI J2033-4723.Comment: 14 pages, 12 figures, published in A&
A multimodal real-time MRI articulatory corpus of French for speech research
In this work we describe the creation of ArtSpeechMRIfr: a real-time as well as static magnetic resonance imaging (rtMRI, 3D MRI) database of the vocal tract. The database contains also processed data: denoised audio, its phonetically aligned annotation, articulatory contours, and vocal tract volume information , which provides a rich resource for speech research. The database is built on data from two male speakers of French. It covers a number of phonetic contexts in the controlled part, as well as spontaneous speech, 3D MRI scans of sustained vocalic articulations, and of the dental casts of the subjects. The corpus for rtMRI consists of 79 synthetic sentences constructed from a phonetized dictionary that makes possible to shorten the duration of acquisitions while keeping a very good coverage of the phonetic contexts which exist in French. The 3D MRI includes acquisitions for 12 French vowels and 10 consonants, each of which was pronounced in several vocalic contexts. Ar-ticulatory contours (tongue, jaw, epiglottis, larynx, velum, lips) as well as 3D volumes were manually drawn for a part of the images
COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses IX. Time delays, lens dynamics and baryonic fraction in HE 0435-1223
We present accurate time delays for the quadruply imaged quasar HE 0435-1223.
The delays were measured from 575 independent photometric points obtained in
the R-band between January 2004 and March 2010. With seven years of data, we
clearly show that quasar image A is affected by strong microlensing variations
and that the time delays are best expressed relative to quasar image B. We
measured Delta_t(BC) = 7.8+/-0.8 days, Delta_t(BD) = -6.5+/-0.7 days and
Delta_t_CD = -14.3+/-0.8 days. We spacially deconvolved HST NICMOS2 F160W
images to derive accurate astrometry of the quasar images and to infer the
light profile of the lensing galaxy. We combined these images with a stellar
population fitting of a deep VLT spectrum of the lensing galaxy to estimate the
baryonic fraction, , in the Einstein radius. We measured f_b =
0.65+0.13-0.10 if the lensing galaxy has a Salpeter IMF and f_b =
0.45+0.04-0.07 if it has a Kroupa IMF. The spectrum also allowed us to estimate
the velocity dispersion of the lensing galaxy, sigma_ap = 222+/-34 km/s. We
used f_b and sigma_ap to constrain an analytical model of the lensing galaxy
composed of an Hernquist plus generalized NFW profile. We solve the Jeans
equations numerically for the model and explored the parameter space under the
additional requirement that the model must predict the correct astrometry for
the quasar images. Given the current error bars on f_b and sigma_ap, we did not
constrain H0 yet with high accuracy, i.e., we found a broad range of models
with chi^2 < 1. However, narrowing this range is possible, provided a better
velocity dispersion measurement becomes available. In addition, increasing the
depth of the current HST imaging data of HE 0435-1223 will allow us to combine
our constraints with lens reconstruction techniques that make use of the full
Einstein ring that is visible in this object.Comment: 12 pages, 10 figures, final version accepted for publication by A&
COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses XIII: Time delays and 9-yr optical monitoring of the lensed quasar RX J1131-1231
We present the results from nine years of optically monitoring the
gravitationally lensed z=0.658 quasar RX J1131-1231. The R-band light curves of
the four individual images of the quasar were obtained using deconvolution
photometry for a total of 707 epochs. Several sharp quasar variability features
strongly constrain the time delays between the quasar images. Using three
different numerical techniques, we measure these delays for all possible pairs
of quasar images while always processing the four light curves simultaneously.
For all three methods, the delays between the three close images A, B, and C
are compatible with being 0, while we measure the delay of image D to be 91
days, with a fractional uncertainty of 1.5% (1 sigma), including systematic
errors. Our analysis of random and systematic errors accounts in a realistic
way for the observed quasar variability, fluctuating microlensing magnification
over a broad range of temporal scales, noise properties, and seasonal gaps.
Finally, we find that our time-delay measurement methods yield compatible
results when applied to subsets of the data.Comment: 11 pages, 9 figures, minor additions to the text only, techniques and
results remain unchanged, A&A in pres
Time delays for 11 gravitationally lensed quasars revisited
We test the robustness of published time delays for 11 lensed quasars by
using two techniques to measure time shifts in their light curves.
We chose to use two fundamentally different techniques to determine time
delays in gravitationally lensed quasars: a method based on fitting a numerical
model and another one derived from the minimum dispersion method introduced by
Pelt and collaborators. To analyse our sample in a homogeneous way and avoid
bias caused by the choice of the method used, we apply both methods to 11
different lensed systems for which delays have been published: JVAS B0218+357,
SBS 0909+523, RX J0911+0551, FBQS J0951+2635, HE 1104-1805, PG 1115+080, JVAS
B1422+231, SBS 1520+530, CLASS B1600+434, CLASS B1608+656, and HE 2149-2745
Time delays for three double lenses, JVAS B0218+357, HE 1104-1805, and CLASS
B1600+434, as well as the quadruply lensed quasar CLASS B1608+656 are confirmed
within the error bars. We correct the delay for SBS 1520+530. For PG 1115+080
and RX J0911+0551, the existence of a second solution on top of the published
delay is revealed. The time delays in four systems, SBS 0909+523, FBQS
J0951+2635, JVAS B1422+231, and HE 2149-2745 prove to be less reliable than
previously claimed.
If we wish to derive an estimate of H_0 based on time delays in
gravitationally lensed quasars, we need to obtain more robust light curves for
most of these systems in order to achieve a higher accuracy and robustness on
the time delays
COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses III. Redshift of the lensing galaxy in eight gravitationally lensed quasars
Aims: We measure the redshift of the lensing galaxy in eight gravitationally
lensed quasars in view of determining the Hubble parameter H_0 from the time
delay method.
Methods: Deep VLT/FORS1 spectra of lensed quasars are spatially deconvolved
in order to separate the spectrum of the lensing galaxies from the glare of the
much brighter quasar images. A new observing strategy is devised. It involves
observations in Multi-Object-Spectroscopy (MOS) which allows the simultaneous
observation of the target and of several PSF and flux calibration stars. The
advantage of this method over traditional long-slit observations is a much more
reliable extraction and flux calibration of the spectra.
Results: For the first time we measure the redshift of the lensing galaxy in
three multiply-imaged quasars: SDSS J1138+0314 (z=0.445), SDSS J1226-0006
(z=0.517), SDSS J1335+0118 (z=0.440), and we give a tentative estimate of the
redshift of the lensing galaxy in Q 1355-2257 (z=0.701). We confirm four
previously measured redshifts: HE 0047-1756 (z=0.407), HE 0230-2130 (z=0.523),
HE 0435-1223 (z=0.454) and WFI J2033-4723 (z=0.661). In addition, we determine
the redshift of the second lensing galaxy in HE 0230-2130 (z=0.526). The
spectra of all lens galaxies are typical for early-type galaxies, except for
the second lensing galaxy in HE 0230-2130 which displays prominent [OII]
emission.Comment: 9 pages, 19 figures, accepted for publication in A&
COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses VIII. Deconvolution of high resolution near-IR images and simple mass models for 7 gravitationally lensed quasars
We apply the iterative MCS deconvolution method (ISMCS) to near-IR HST
archives data of seven gravitationally lensed quasars currently monitored by
the COSMOGRAIL collaboration: HE 0047-1756, RX J1131-1231, SDSS J1138+0314,
SDSS J1155+6346, SDSS J1226-0006, WFI J2026-4536 and HS 2209+1914. In doing so,
we obtain relative positions for the lensed images and shape parameters for the
light distribution of the lensing galaxy in each system. The lensed image
positions are derived with 1-2 mas accuracy. To predict time delays and to test
the ability of simple mass models to reproduce the observed configuration,
isothermal and de Vaucouleurs mass models are calculated for the whole sample
using state-of-the-art modeling techniques. The effect of the lens environment
on the lens mass models is taken into account with a shear term. Doubly imaged
quasars are equally well fitted by each of these models. A large amount of
shear is necessary to reproduce SDSS J1155+6346 and SDSS J1226-006. In the
latter case, we identify a nearby galaxy as the dominant source of shear. The
quadruply imaged quasar SDSS J1138+0314 is well reproduced by simple lens
models, which is not the case for the two other quads, RX J1131-1231 and WFI
J2026-4536. This might be the signature of astrometric perturbations due to
massive substructures in the lensing galaxy unaccounted for by the models.
Other possible explanations are also presented.Comment: 14 pages, 1 figure (with 28 frames), 5 tables, accepted for
publication in Astronomy & Astrophysics (08/07/2010
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
Bayesian approach to gravitational lens model selection: constraining H_0 with a selected sample of strong lenses
Bayesian model selection methods provide a self-consistent probabilistic
framework to test the validity of competing scenarios given a set of data. We
present a case study application to strong gravitational lens parametric
models. Our goal is to select a homogeneous lens subsample suitable for
cosmological parameter inference. To this end we apply a Bayes factor analysis
to a synthetic catalog of 500 lenses with power-law potential and external
shear. For simplicity we focus on double-image lenses (the largest fraction of
lens in the simulated sample) and select a subsample for which astrometry and
time-delays provide strong evidence for a simple power-law model description.
Through a likelihood analysis we recover the input value of the Hubble constant
to within 3\sigma statistical uncertainty. We apply this methodology to a
sample of double image lensed quasars. In the case of B1600+434, SBS 1520+530
and SDSS J1650+4251 the Bayes' factor analysis favors a simple power-law model
description with high statistical significance. Assuming a flat \LambdaCDM
cosmology, the combined likelihood data analysis of such systems gives the
Hubble constant H_0=76+15-5 km/s/Mpc having marginalized over the lens model
parameters, the cosmic matter density and consistently propagated the
observational errors on the angular position of the images. The next generation
of cosmic structure surveys will provide larger lens datasets and the method
described here can be particularly useful to select homogeneous lens subsamples
adapted to perform unbiased cosmological parameter inferenceComment: 13 pages; 13 figures; includes Bayesian analysis of a synthetic lens
catalog generated with GRAVLENS, several additional results; matches MNRAS
accepted versio
COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses V. The time delay in SDSS J1650+4251
Aims: Our aim is to measure the time delay between the two gravitationally
lensed images of the z = 1.547 quasar SDSS J1650+4251, in order to estimate the
Hubble constant H_0.
Methods: Our measurement is based on R-band light curves with 57 epochs
obtained at Maidanak Observatory, in Uzbekistan, from May 2004 to September
2005. The photometry is performed using simultaneous deconvolution of the data,
which provides the individual light curves of the otherwise blended quasar
images. The time delay is determined from the light curves using two very
different numerical techniques, i.e., polynomial fitting and direct
cross-correlation. The time delay is converted into H_0 following analytical
modeling of the potential well.
Results: Our best estimate of the time delay is Dt = 49.5 +/- 1.9 days, i.e.,
we reach a 3.8% accuracy. The R-band flux ratio between the quasar images,
corrected for the time delay and for slow microlensing, is F_A /F_B = 6.2 +/-
5%.
Conclusions: The accuracy reached on the time delay allows us to discriminate
well between families of lens models. As for most other multiply imaged
quasars, only models of the lensing galaxy that have a de Vaucouleurs mass
profile plus external shear give a Hubble constant compatible with the current
most popular value (H_0 = 72 +/- 8 km s-1 Mpc-1). A more realistic singular
isothermal sphere model plus external shear gives H_0 = 51.7 +4.0 -3.0 km s-1
Mpc-1.Comment: 8 pages, 12 figures, accepted by A&