349 research outputs found
Cosmography from two-image lens systems: overcoming the lens profile slope degeneracy
The time delays between the multiple images of a strong lens system, together
with a model of the lens mass distribution, allow a one-step measurement of a
cosmological distance, namely, the "time-delay distance" of the lens (D_dt)
that encodes cosmological information. The time-delay distance depends
sensitively on the radial profile slope of the lens mass distribution;
consequently, the lens slope must be accurately constrained for cosmological
studies. We show that the slope cannot be constrained in two-image systems with
single-component compact sources, whereas it can be constrained in systems with
two-component sources provided the separation between the image components can
be measured with milliarcsecond precisions, which is not feasible in most
systems. In contrast, we demonstrate that spatially extended images of the
source galaxy in two-image systems break the radial slope degeneracy and allow
D_dt to be measured with uncertainties of a few percent. Deep and
high-resolution imaging of the lens systems are needed to reveal the extended
arcs, and stable point spread functions are required for our lens modelling
technique. Two-image systems, no longer plagued by the radial profile slope
degeneracy, would augment the sample of useful time-delay lenses by a factor of
~6, providing substantial advances for cosmological studies.Comment: 14 pages, 9 figures, revisions based on referee's comments, accepted
for publication in MNRA
The inner dark matter distribution of the Cosmic Horseshoe (J1148+1930) with gravitational lensing and dynamics
We present a detailed analysis of the inner mass structure of the Cosmic
Horseshoe (J1148+1930) strong gravitational lens system observed with the
Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3). In addition to the
spectacular Einstein ring, this systems shows a radial arc. We obtained the
redshift of the radial arc counter image from
Gemini observations. To disentangle the dark and luminous matter, we consider
three different profiles for the dark matter distribution: a power-law profile,
the NFW, and a generalized version of the NFW profile. For the luminous matter
distribution, we base it on the observed light distribution that is fitted with
three components: a point mass for the central light component resembling an
active galactic nucleus, and the remaining two extended light components scaled
by a constant M/L. To constrain the model further, we include published
velocity dispersion measurements of the lens galaxy and perform a
self-consistent lensing and axisymmetric Jeans dynamical modeling. Our model
fits well to the observations including the radial arc, independent of the dark
matter profile. Depending on the dark matter profile, we get a dark matter
fraction between 60 % and 70 %. With our composite mass model we find that the
radial arc helps to constrain the inner dark matter distribution of the Cosmic
Hoseshoe independently of the dark matter profile.Comment: 19 pages, 14 figures, 8 tables, submitted to A&
A seven square degrees survey for galaxy-scale gravitational lenses with the HST imaging archive
We present the results of a visual search for galaxy-scale gravitational
lenses in nearly 7 square degrees of Hubble Space Telescope (HST) images. The
dataset comprises the whole imaging data ever taken with the Advanced Camera
for Surveys (ACS) in the filter F814W (I-band) up to August 31st, 2011, i.e.
6.03 square degrees excluding the field of the Cosmic Evolution Survey (COSMOS)
which has been the subject of a separate visual search. In addition, we have
searched for lenses in the whole Wide Field Camera 3 (WFC3) near-IR imaging
dataset in all filters (1.01 square degrees) up to the same date. Our primary
goal is to provide a sample of lenses with a broad range of different
morphologies and lens-source brightness contrast in order estimate a lower
limit to the number of galaxy-scale strong lenses in the future Euclid survey
in its VIS band. Our criteria to select lenses are purely morphological as we
do not use any colour or redshift information.The final candidate selection is
very conservative hence leading to a nearly pure but incomplete sample. We find
49 new lens candidates: 40 in the ACS images and 9 in the WFC3 images. Out of
these, 16 candidates are secure lenses owing to their striking morphology, 21
more are very good candidates, and 12 more have morphologies compatible with
gravitational lensing but also compatible with other astrophysical objects. It
is therefore insensitive to cosmic variance and allows to estimate the number
of galaxy-scale strong lenses on the sky for a putative survey depth, which is
the main result of the present work. Because of the incompleteness of the
sample, the estimated lensing rates should be taken as lower limits. Using
these, we anticipate that a 15 000 square degrees space survey such as Euclid
will find at least 60 000 galaxy-scale strong lenses down to a limiting AB
magnitude of I = 24.5 (10-sigma) or I = 25.8 (3-sigma).Comment: 13 pages, 12 figures, Accepted for publication in MNRA
The Hubble Constant determined through an inverse distance ladder including quasar time delays and Type Ia supernovae
Context. The precise determination of the present-day expansion rate of the
Universe, expressed through the Hubble constant , is one of the most
pressing challenges in modern cosmology. Assuming flat CDM,
inference at high redshift using cosmic-microwave-background data from Planck
disagrees at the 4.4 level with measurements based on the local
distance ladder made up of parallaxes, Cepheids and Type Ia supernovae (SNe
Ia), often referred to as "Hubble tension". Independent,
cosmological-model-insensitive ways to infer are of critical importance.
Aims. We apply an inverse-distance-ladder approach, combining strong-lensing
time-delay-distance measurements with SN Ia data. By themselves, SNe Ia are
merely good relative distance indicators, but by anchoring them to strong
gravitational lenses one can obtain an measurement that is relatively
insensitive to other cosmological parameters. Methods. A cosmological parameter
estimate is performed for different cosmological background models, both for
strong-lensing data alone and for the combined lensing + SNe Ia data sets.
Results. The cosmological-model dependence of strong-lensing measurements
is significantly mitigated through the inverse distance ladder. In combination
with SN Ia data, the inferred consistently lies around 73-74 km s
Mpc, regardless of the assumed cosmological background model. Our
results agree nicely with those from the local distance ladder, but there is a
>2 tension with Planck results, and a ~1.5 discrepancy with
results from an inverse distance ladder including Planck, Baryon Acoustic
Oscillations and SNe Ia. Future strong-lensing distance measurements will
reduce the uncertainties in from our inverse distance ladder.Comment: 5 pages, 3 figures, A&A letters accepted versio
The Halos of Satellite Galaxies: the Companion of the Massive Elliptical Lens SL2S J08544-0121
Strong gravitational lensing by groups or clusters of galaxies provides a
powerful technique to measure the dark matter properties of individual lens
galaxies. We study in detail the mass distribution of the satellite lens galaxy
in the group-scale lens SL2S J08544-0121 by modelling simultaneously the
spatially extended surface brightness distribution of the source galaxy and the
lens mass distribution using Markov chain Monte Carlo methods. In particular,
we measure the dark matter halo size of the satellite lens galaxy to be
6.0^{+2.9}_{-2.0} kpc with a fiducial velocity dispersion of 127^{+21}_{-12}
km/s. This is the first time the size of an individual galaxy halo in a galaxy
group has been measured using strong gravitational lensing without assumptions
of mass following light. We verify the robustness of our halo size measurement
using mock data resembling our lens system. Our measurement of the halo size is
compatible with the estimated tidal radius of the satellite galaxy, suggesting
that halos of galaxies in groups experience significant tidal stripping, a
process that has been previously observed on galaxies in clusters. Our mass
model of the satellite galaxy is elliptical with its major axis misaligned with
that of the light by ~50 deg. The major axis of the total matter distribution
is oriented more towards the centre of the host halo, exhibiting the radial
alignment found in N-body simulations and observational studies of satellite
galaxies. This misalignment between mass and light poses a significant
challenge to modified Newtonian dynamics.Comment: 13 pages, 10 figures, minor revisions based on referee's comments,
accepted for publication in A&
GLaD: Gravitational Lensing and Dynamics, combined analysis to unveil properties of high-redshift galaxies
Dynamical modelling of Integral-Field-Unit (IFU) stellar kinematics is a
powerful tool to unveil the dynamical structure and mass build-up of galaxies
in the local Universe, while gravitational lensing is nature's cosmic telescope
to explore the properties of galaxies beyond the local Universe. We present a
new approach which unifies dynamical modelling of galaxies with the
magnification power of strong gravitational lensing, to reconstruct the
structural and dynamical properties of high-redshift galaxies. By means of
axisymmetric Jeans modelling, we create a dynamical model of the source galaxy,
assuming a surface brightness and surface mass density profile. We then predict
how the source's surface brightness and kinematics would look like when lensed
by the foreground mass distribution and compare with the mock observed arcs of
strong gravitational lensing systems. For demonstration purposes, we create and
analyse mock data of the strong lensing system RX J1131-1231. By modelling both
the lens and source, we recover the dynamical mass within the effective radius
of strongly lensed high-redshift sources within 5% uncertainty, and we improve
the constraints on the lens mass parameters by up to 50%. This machinery is
particularly well suited for future observations from large segmented-mirror
telescopes, such as the James Webb Space Telescope, that will yield high
sensitivity and angular-resolution IFU data for studying distant and faint
galaxies.Comment: 16 pages, 13 figure
A new method to measure evolution of the galaxy luminosity function
We present a new efficient technique for measuring evolution of the galaxy
luminosity function. The method reconstructs the evolution over the
luminosity-redshift plane using any combination of three input dataset types:
1) number counts, 2) galaxy redshifts, 3) integrated background flux
measurements. The evolution is reconstructed in adaptively sized regions of the
plane according to the input data as determined by a Bayesian formalism. We
demonstrate the performance of the method using a range of different synthetic
input datasets. We also make predictions of the accuracy with which forthcoming
surveys conducted with SCUBA2 and the Herschel Space Satellite will be able to
measure evolution of the sub-millimetre luminosity function using the method.Comment: MNRAS in press. 14 pages, 7 figures
HOLISMOKES -- X. Comparison between neural network and semi-automated traditional modeling of strong lenses
Modeling of strongly gravitationally lensed galaxies is often required in
order to use them as astrophysical or cosmological probes. With current and
upcoming wide-field imaging surveys, the number of detected lenses is
increasing significantly such that automated and fast modeling procedures for
ground-based data are urgently needed. This is especially pertinent to
short-lived lensed transients in order to plan follow-up observations.
Therefore, we present in a companion paper (submitted) a neural network
predicting the parameter values with corresponding uncertainties of a Singular
Isothermal Ellipsoid (SIE) mass profile with external shear. In this work, we
present a newly-developed pipeline glee_auto.py to model consistently any
galaxy-scale lensing system. In contrast to previous automated modeling
pipelines that require high-resolution images, glee_auto.py is optimized for
ground-based images such as those from the Hyper-Suprime-Cam (HSC) or the
upcoming Rubin Observatory Legacy Survey of Space and Time. We further present
glee_tools.py, a flexible automation code for individual modeling that has no
direct decisions and assumptions implemented. Both pipelines, in addition to
our modeling network, minimize the user input time drastically and thus are
important for future modeling efforts. We apply the network to 31 real
galaxy-scale lenses of HSC and compare the results to the traditional models.
In the direct comparison, we find a very good match for the Einstein radius
especially for systems with ". The lens mass center and
ellipticity show reasonable agreement. The main discrepancies are on the
external shear as expected from our tests on mock systems. In general, our
study demonstrates that neural networks are a viable and ultra fast approach
for measuring the lens-galaxy masses from ground-based data in the upcoming era
with lenses expected.Comment: 17+28 pages, 7+31 figures, 2+5 tables, submitted to A&
Disentangling Baryons and Dark Matter in the Spiral Gravitational Lens B1933+503
Measuring the relative mass contributions of luminous and dark matter in
spiral galaxies is important for understanding their formation and evolution.
The combination of a galaxy rotation curve and strong lensing is a powerful way
to break the disk-halo degeneracy that is inherent in each of the methods
individually. We present an analysis of the 10-image radio spiral lens
B1933+503 at z_l=0.755, incorporating (1) new global VLBI observations, (2) new
adaptive-optics assisted K-band imaging, (3) new spectroscopic observations for
the lens galaxy rotation curve and the source redshift. We construct a
three-dimensionally axisymmetric mass distribution with 3 components: an
exponential profile for the disk, a point mass for the bulge, and an NFW
profile for the halo. The mass model is simultaneously fitted to the kinematics
and the lensing data. The NFW halo needs to be oblate with a flattening of
a/c=0.33^{+0.07}_{-0.05} to be consistent with the radio data. This suggests
that baryons are effective at making the halos oblate near the center. The
lensing and kinematics analysis probe the inner ~10 kpc of the galaxy, and we
obtain a lower limit on the halo scale radius of 16 kpc (95% CI). The dark
matter mass fraction inside a sphere with a radius of 2.2 disk scale lengths is
f_{DM,2.2}=0.43^{+0.10}_{-0.09}. The contribution of the disk to the total
circular velocity at 2.2 disk scale lengths is 0.76^{+0.05}_{-0.06}, suggesting
that the disk is marginally submaximal. The stellar mass of the disk from our
modeling is log_{10}(M_{*}/M_{sun}) = 11.06^{+0.09}_{-0.11} assuming that the
cold gas contributes ~20% to the total disk mass. In comparison to the stellar
masses estimated from stellar population synthesis models, the stellar initial
mass function of Chabrier is preferred to that of Salpeter by a probability
factor of 7.2.Comment: 16 pages, 13 figures, minor revisions based on referee's comments,
accepted for publication in Ap
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