2,600 research outputs found
Mass along the Line of Sight to the Gravitational Lens B1608+656: Galaxy Groups and Implications for H_0
We report the discovery of four groups of galaxies along the line of sight to the B1608+656 gravitational lens system. One group is at the redshift of the primary lensing galaxy (z = 0.631) and appears to have a low mass, with eight spectroscopically confirmed members and an estimated velocity dispersion of 150 ± 60 km s^(-1). The three other groups are in the foreground of the lens. These groups contain ~10 confirmed members each and are located at redshifts of 0.265, 0.426, and 0.52. Two of the three additional groups are centered roughly on the lens system, while the third is centered ~1' south of the lens. We investigate the effect of each of the four groups on the gravitational lensing potential of the B1608+656 system, with a particular focus on the implications for the value of H_0 derived from this system. We find that each group provides an external convergence of ~0.005-0.060, depending on the assumptions made in the calculation. For the B1608+656 system, the stellar velocity dispersion of the lensing galaxy has been measured, thus breaking the mass sheet degeneracy due to the group that is physically associated with the lens. The effect of the other groups along the line of sight can be folded into the overall uncertainties due to large-scale structure (LSS) along the line of sight. Because B1608+656 appears to lie along an overdense line of sight, the LSS will cause the measurement of H_0 to be biased high for this system. This effect could be 5% or greater
Probing dark matter substructure in the gravitational lens HE0435-1223 with the WFC3 grism
Strong gravitational lensing provides a powerful test of Cold Dark Matter
(CDM) as it enables the detection and mass measurement of low mass haloes even
if they do not contain baryons. Compact lensed sources such as Active Galactic
Nuclei (AGN) are particularly sensitive to perturbing subhalos, but their use
as a test of CDM has been limited by the small number of systems which have
significant radio emission which is extended enough avoid significant lensing
by stars in the plane of the lens galaxy, and red enough to be minimally
affected by differential dust extinction. Narrow-line emission is a promising
alternative as it is also extended and, unlike radio, detectable in virtually
all optically selected AGN lenses. We present first results from a WFC3 grism
narrow-line survey of lensed quasars, for the quadruply lensed AGN HE0435-1223.
Using a forward modelling pipeline which enables us to robustly account for
spatial blending, we measure the [OIII] 5007 \AA~ flux ratios of the four
images. We find that the [OIII] fluxes and positions are well fit by a simple
smooth mass model for the main lens. Our data rule out a NFW perturber projected within 1\farcs0 (0\farcs1)
arcseconds of each of the lensed images, where is the perturber mass
within its central 600 pc. The non-detection is broadly consistent with the
expectations of CDM for a single system. The sensitivity achieved
demonstrates that powerful limits on the nature of dark matter can be obtained
with the analysis of narrow-line lenses.Comment: Accepted for publication in MNRAS, 15 pages, 8 figure
Probing sub-galactic mass structure with the power spectrum of surface-brightness anomalies in high-resolution observations of galaxy–galaxy strong gravitational lenses. II. Observational constraints on the subgalactic matter power spectrum
Stringent observational constraints on the subgalactic matter power spectrum would allow one to distinguish between the concordance ΛCDM and the various alternative dark-matter models that predict significantly different properties of mass structure in galactic haloes. Galaxy–galaxy strong gravitational lensing provides a unique opportunity to probe the subgalactic mass structure in lens galaxies beyond the Local Group. Here, we demonstrate the first application of a novel methodology to observationally constrain the subgalactic matter power spectrum in the inner regions of massive elliptical lens galaxies on 1–10 kpc scales from the power spectrum of surface-brightness anomalies in highly magnified galaxy-scale Einstein rings and gravitational arcs. The pilot application of our approach to Hubble Space Telescope (HST/WFC3/F390W) observations of the SLACS lens system SDSS J0252+0039 allows us to place the following observational constraints (at the 99 per cent confidence level) on the dimensionless convergence power spectrum Δ2δκ and the standard deviation in the aperture mass σAM: Δ2δκ < 1 (σAM < 0.8 × 108 M⊙) on 0.5-kpc scale, Δ2δκ < 0.1 (σAM < 1 × 108 M⊙) on 1-kpc scale and Δ2δκ < 0.01 (σAM < 3 × 108 M⊙) on 3-kpc scale. These first upper-limit constraints still considerably exceed the estimated effect of CDM subhaloes. However, future analysis of a larger sample of galaxy–galaxy strong lens systems can substantially narrow down these limits and possibly rule out dark-matter models that predict a significantly higher level of density fluctuations on the critical subgalactic scales.</p
Probing sub-galactic mass structure with the power spectrum of surface-brightness anomalies in high-resolution observations of galaxy-galaxy strong gravitational lenses – I. Power-spectrum measurement and feasibility study
While the direct detection of the dark-matter particle remains very challenging, the nature of dark matter could be possibly constrained by comparing the observed abundance and properties of small-scale sub-galactic mass structures with predictions from the phenomenological dark-matter models, such as cold, warm, or hot dark matter. Galaxy-galaxy strong gravitational lensing provides a unique opportunity to search for tiny surface-brightness anomalies in the extended lensed images (i.e. Einstein rings or gravitational arcs), induced by possible small-scale mass structures in the foreground lens galaxy. In this paper, the first in a series, we introduce and test a methodology to measure the power spectrum of such surface-brightness anomalies from high-resolution Hubble Space Telescope (HST) imaging. In particular, we focus on the observational aspects of this statistical approach, such as the most suitable observational strategy and sample selection, the choice of modelling techniques, and the noise correction. We test the feasibility of the power-spectrum measurement by applying it to a sample of galaxy-galaxy strong gravitational lens systems from the Sloan Lens ACS Survey, with the most extended, bright, high-signal-to-noise-ratio lensed images, observed in the rest-frame ultraviolet. In the companion paper, we present the methodology to relate the measured power spectrum to the statistical properties of the underlying small-scale mass structures in the lens galaxy and infer the first observational constraints on the sub-galactic matter power spectrum in a massive elliptical (lens) galaxy.</p
The central image of a gravitationally lensed quasar
A galaxy can act as a gravitational lens, producing multiple images of a
background object. Theory predicts there should be an odd number of images but,
paradoxically, almost all observed lenses have 2 or 4 images. The missing image
should be faint and appear near the galaxy's center. These ``central images''
have long been sought as probes of galactic cores too distant to resolve with
ordinary observations. There are five candidates, but in one case the third
image is not necessarily a central image, and in the others, the central
component might be a foreground source rather than a lensed image. Here we
report the most secure identification of a central image, based on radio
observations of PMN J1632-0033, one of the latter candidates. Lens models
incorporating the central image show that the mass of the lens galaxy's central
black hole is less than 2 x 10^8 M_sun, and the galaxy's surface density at the
location of the central image is more than 20,000 M_sun per square parsec, in
agreement with expectations based on observations of galaxies hundreds of times
closer to the Earth.Comment: Nature, in press [7 pp, 2 figs]. Standard media embargo applies
before publicatio
Sub-kiloparsec Imaging of Cool Molecular Gas in Two Strongly Lensed Dusty, Star-Forming Galaxies
We present spatially-resolved imaging obtained with the Australia Telescope
Compact Array (ATCA) of three CO lines in two high-redshift gravitationally
lensed dusty star-forming galaxies, discovered by the South Pole Telescope.
Strong lensing allows us to probe the structure and dynamics of the molecular
gas in these two objects, at z=2.78 and z=5.66, with effective source-plane
resolution of less than 1kpc. We model the lensed emission from multiple CO
transitions and the dust continuum in a consistent manner, finding that the
cold molecular gas as traced by low-J CO always has a larger half-light radius
than the 870um dust continuum emission. This size difference leads to up to 50%
differences in the magnification factor for the cold gas compared to dust. In
the z=2.78 galaxy, these CO observations confirm that the background source is
undergoing a major merger, while the velocity field of the other source is more
complex. We use the ATCA CO observations and comparable resolution Atacama
Large Millimeter/submillimeter Array dust continuum imaging of the same objects
to constrain the CO-H_2 conversion factor with three different procedures,
finding good agreement between the methods and values consistent with those
found for rapidly star-forming systems. We discuss these galaxies in the
context of the star formation - gas mass surface density relation, noting that
the change in emitting area with observed CO transition must be accounted for
when comparing high-redshift galaxies to their lower redshift counterparts.Comment: 14 pages, 7 figures; accepted for publication in Ap
COSMOGRAIL XVIII: time delays of the quadruply lensed quasar WFI2033-4723
We present new measurements of the time delays of WFI2033-4723. The data sets
used in this work include 14 years of data taken at the 1.2m Leonhard Euler
Swiss telescope, 13 years of data from the SMARTS 1.3m telescope at Las
Campanas Observatory and a single year of high-cadence and high-precision
monitoring at the MPIA 2.2m telescope. The time delays measured from these
different data sets, all taken in the R-band, are in good agreement with each
other and with previous measurements from the literature. Combining all the
time-delay estimates from our data sets results in Dt_AB = 36.2-0.8+0.7 days
(2.1% precision), Dt_AC = -23.3-1.4+1.2 days (5.6%) and Dt_BC = -59.4-1.3+1.3
days (2.2%). In addition, the close image pair A1-A2 of the lensed quasars can
be resolved in the MPIA 2.2m data. We measure a time delay consistent with zero
in this pair of images. We also explore the prior distributions of microlensing
time-delay potentially affecting the cosmological time-delay measurements of
WFI2033-4723. There is however no strong indication in our measurements that
microlensing time delay is neither present nor absent. This work is part of a
H0LiCOW series focusing on measuring the Hubble constant from WFI2033-4723.Comment: Submitted to Astronomy and Astrophysic
B0850+054: a new gravitational lens system from CLASS
We report the discovery of a new gravitational lens system from the CLASS
survey. Radio observations with the VLA, the WSRT and MERLIN show that the
radio source B0850+054 is comprised of two compact components with identical
spectra, a separation of 0.7 arcsec and a flux density ratio of 6:1. VLBA
observations at 5 GHz reveal structures that are consistent with the
gravitational lens hypothesis. The brighter of the two images is resolved into
a linear string of at least six sub-components whilst the weaker image is
radially stretched towards the lens galaxy. UKIRT K-band imaging detects an
18.7 mag extended object, but the resolution of the observations is not
sufficient to resolve the lensed images and the lens galaxy. Mass modelling has
not been possible with the present data and the acquisition of high-resolution
optical data is a priority for this system.Comment: 5 pages, 4 figures, accepted for publication in MNRA
IFC (incl. Editorial board)
We present a weak gravitational lensing measurement of the external
convergence along the line of sight to the quadruply lensed quasar
HE04351223. Using deep r-band images from Subaru-Suprime-Cam we observe
galaxies down to a 3 limiting magnitude of mags resulting in
a source galaxy density of 14 galaxies / arcmin after redshift-based cuts.
Using an inpainting technique and Multi-Scale Entropy filtering algorithm, we
find that the region in close proximity to the lens has an estimated external
convergence of and is hence marginally
under-dense. We also rule out the presence of any halo with a mass greater than
(68 confidence limit). Our
results, consistent with previous studies of this lens, confirm that the
intervening mass along the line of sight to HE04351223 does not affect
significantly the cosmological results inferred from the time delay
measurements of that specific object.Comment: 14 pages, 8 figures, 2 table
Small scale spatial variability of snow density and depth over complex alpine terrain: Implications for estimating snow water equivalent
This study analyzes spatial variability of snow depth and density from measurements made in February and April of 2010 and 2011 in three 1–2 km2 areas within a valley of the central Spanish Pyrenees. Snow density was correlated with snow depth and different terrain characteristics. Regression models were used to predict the spatial variability of snow density, and to assess how the error in computed densities might influence estimates of snow water equivalent (SWE). The variability in snow depth was much greater than that of snow density. The average snow density was much greater in April than in February. The correlations between snow depth and density were generally statistically significant but typically not very high, and their magnitudes and signs were highly variable among sites and surveys. The correlation with other topographic variables showed the same variability in magnitude and sign, and consequently the resulting regression models were very inconsistent, and in general explained little of the variance. Antecedent climatic and snow conditions prior to each survey help highlight the main causes of the contrasting relation shown between snow depth, density and terrain. As a consequence of the moderate spatial variability of snow density relative to snow depth, the absolute error in the SWE estimated from computed densities using the regression models was generally less than 15%. The error was similar to that obtained by relating snow density measurements directly to adjacent snow depths.This work was supported by research projects CGL2011-27536/HID: “Hidrologia nival en el Pirineo central español: variabilidad espacial, importancia hidrológica y su respuesta a la variabilidad y cambio climático”, financed by the Spanish Commission of Science and Technology, and FEDER; ACQWA (FP7-ENV- 2008-1-212250); the projects “La nieve en el Pirineo aragonés: Distribución especial y su respuesta a las condiciones climáticas” and “Efecto de los escenarios de cambio climático sobre la hidrología superficial y la gestión de embalses del Pirineo Aragonés”, financed by “Obra Social La Caixa”; and “Influencia del cambio climático en el turismo de nieve-CTTP1/10”, financed by the Comunidad de Trabajo de los Pirineos, CTP.Peer Reviewe
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