2,821 research outputs found
A determination of H_0 with the CLASS gravitational lens B1608+656: II. Mass models and the Hubble constant from lensing
EDITED FROM PAPER: We present mass models of the four-image gravitational
lens system B1608+656. A mass model for the lens galaxies has been determined
that reproduces the image positions, two out of three flux-density ratios and
the model time delays.
Using the time delays determined by Fassnacht et al. (1999a), we find that
the best isothermal mass model gives H_0=59^{+7}_{-6} km/s/Mpc for Omega_m=1
and Omega_l=0.0, or H_0=(65-63)^{+7}_{-6} km/s/Mpc for Omega_m=0.3 and Omega_l
= 0.0-0.7 (95.4% statistical confidence). A systematic error of +/-15 km/s/Mpc
is estimated.
This cosmological determination of H_0 agrees well with determinations from
three other gravitational lens systems (i.e. B0218+357, Q0957+561 and
PKS1830-211), SNe Ia, the S-Z effect and local determinations. The current
agreement on H_0 from four out of five gravitational lens systems (i)
emphasizes the reliability of its determination from isolated gravitational
lens systems and (ii) suggests that a close-to-isothermal mass profile can
describe disk galaxies, ellipticals and central cluster ellipticals.
The average of H_0 from B0218+357, Q0957+561, B1608+656 and PKS1830-211,
gives H_0(GL)=69 +/-7 km/s/Mpc for a flat universe with Omega_m=1 or H_0(GL)=74
+/-8 km/s/Mpc for Omega_m=0.3 and Omega_l=0.0-0.7. When including PG1115+080,
these values decrease to 64 +/-11 km/s/Mpc and 68 +/-13 km/s/Mpc (2-sigma
errors), respectively.Comment: Accepted for publication in ApJ. 34 pages, 4 figure
What drives basin scale spatial variability of snowpack properties in northern Colorado?
This study uses a combination of field measurements and Natural Resource
Conservation Service (NRCS) operational snow data to understand the drivers
of snow density and snow water equivalent (SWE) variability at the basin
scale (100s to 1000s km<sup>2</sup>). Historic snow course snowpack density
observations were analyzed within a multiple linear regression snow density
model to estimate SWE directly from snow depth measurements. Snow surveys
were completed on or about 1 April 2011 and 2012 and combined with NRCS
operational measurements to investigate the spatial variability of SWE near
peak snow accumulation. Bivariate relations and multiple linear regression
models were developed to understand the relation of snow density and SWE
with terrain variables (derived using a geographic information system
(GIS)). Snow density variability was best explained by day of year, snow
depth, UTM Easting, and elevation. Calculation of SWE directly from snow
depth measurement using the snow density model has strong statistical
performance, and model validation suggests the model is transferable to
independent data within the bounds of the original data set. This pathway of
estimating SWE directly from snow depth measurement is useful when
evaluating snowpack properties at the basin scale, where many time-consuming
measurements of SWE are often not feasible. A comparison with a previously
developed snow density model shows that calibrating a snow density model to
a specific basin can provide improvement of SWE estimation at this scale, and
should be considered for future basin scale analyses. During both water year
(WY) 2011 and 2012, elevation and location (UTM Easting and/or UTM Northing)
were the most important SWE model variables, suggesting that orographic
precipitation and storm track patterns are likely driving basin scale SWE
variability. Terrain curvature was also shown to be an important variable,
but to a lesser extent at the scale of interest
Snow depth measurement via time lapse photography and automated image recognition
January 2019.Includes bibliographical references.Seasonal snow is a crucial component of water supply in Colorado and the western United States. Measurement of snow accumulation through the winter and spring allows water managers to forecast water supply for the growing season and take actions to ease flooding and drought. The Natural Resources Conservation Service’s (NRCS) snow telemetry (SNOTEL) network provides real-time data at a high cost per station and at single points. An evaluation of existing field measurements of snow depth taken in 2009 and 2010 was undertaken to determine if fine resolution depth measurements are justified. Fassnacht et al. (in press) showed that the snow depth variability can be substantial even at fine resolution. However, these data required extensive labor to collect and only represented one measurement in time. A low-cost method to measure snow variability around these stations or in underrepresented areas could improve snow forecasts by quantifying the representativeness of data from the current network. To this end, we trialed a method combining time lapse photography and computer vision techniques to find snow depth at five sites in Colorado during water year 2018. Different site configurations were trialed, and a best operating procedure was determined. The data gathered were not more accurate than current ultrasonic or laser snow depth measurement technologies. However, the low cost and versatility of this method may make it more applicable in certain situations
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
Dissecting the Gravitational Lens B1608+656. II. Precision Measurements of the Hubble Constant, Spatial Curvature, and the Dark Energy Equation of State
Strong gravitational lens systems with measured time delays between the
multiple images provide a method for measuring the "time-delay distance" to the
lens, and thus the Hubble constant. We present a Bayesian analysis of the
strong gravitational lens system B1608+656, incorporating (i) new, deep Hubble
Space Telescope (HST) observations, (ii) a new velocity dispersion measurement
of 260+/-15 km/s for the primary lens galaxy, and (iii) an updated study of the
lens' environment. When modeling the stellar dynamics of the primary lens
galaxy, the lensing effect, and the environment of the lens, we explicitly
include the total mass distribution profile logarithmic slope gamma' and the
external convergence kappa_ext; we marginalize over these parameters, assigning
well-motivated priors for them, and so turn the major systematic errors into
statistical ones. The HST images provide one such prior, constraining the lens
mass density profile logarithmic slope to be gamma'=2.08+/-0.03; a combination
of numerical simulations and photometric observations of the B1608+656 field
provides an estimate of the prior for kappa_ext: 0.10 +0.08/-0.05. This latter
distribution dominates the final uncertainty on H_0. Compared with previous
work on this system, the new data provide an increase in precision of more than
a factor of two. In combination with the WMAP 5-year data set, we find that the
B1608+656 data set constrains the curvature parameter to be -0.031 < Omega_k <
0.009 (95% CL), a level of precision comparable to that afforded by the current
Type Ia SNe sample. Asserting a flat spatial geometry, we find that, in
combination with WMAP, H_0 = 69.7 +4.9/-5.0 km/s/Mpc and w=-0.94 +0.17/-0.19
(68% CL), suggesting that the observations of B1608+656 constrain w as tightly
as do the current Baryon Acoustic Oscillation data. (abridged)Comment: 24 pages, 8 figures, revisions based on referee's comments, accepted
for publication in Ap
The Hubble Constant from the Gravitational Lens B1608+656
We present a refined gravitational lens model of the four-image lens system
B1608+656 based on new and improved observational constraints: (i) the three
independent time-delays and flux-ratios from VLA observations, (ii) the
radio-image positions from VLBA observations, (iii) the shape of the
deconvolved Einstein Ring from optical and infrared HST images, (iv) the
extinction-corrected lens-galaxy centroids and structural parameters, and (v) a
stellar velocity dispersion, sigma_ap=247+-35 km/s, of the primary lens galaxy
(G1), obtained from an echelle spectrum taken with the Keck--II telescope. The
lens mass model consists of two elliptical mass distributions with power-law
density profiles and an external shear, totaling 22 free parameters, including
the density slopes which are the key parameters to determine the value of H_0
from lens time delays. This has required the development of a new lens code
that is highly optimized for speed. The minimum-chi^2 model reproduces all
observations very well, including the stellar velocity dispersion and the shape
of the Einstein Ring. A combined gravitational-lens and stellar dynamical
analysis leads to a value of the Hubble Constant of H_0=75(+7/-6) km/s/Mpc (68
percent CL; Omega_m=0.3, Omega_Lambda=0.7. The non-linear error analysis
includes correlations between all free parameters, in particular the density
slopes of G1 and G2, yielding an accurate determination of the random error on
H_0. The lens galaxy G1 is ~5 times more massive than the secondary lens galaxy
(G2), and has a mass density slope of gamma_G1=2.03(+0.14/-0.14) +- 0.03 (68
percent CL) for rho~r^-gamma', very close to isothermal (gamma'=2). (Abridged)Comment: 17 pages, 6 figures, 5 tables; revised version with correct fig.6 and
clarified text based on referee report; conclusions unchange
Flow modelling to estimate suspended sediment travel times for two Canadian Deltas
International audienceThe approximate travel times for suspended sediment transport through two multi-channel networks are estimated using flow modelling. The focus is on the movement of high sediment concentrations that travel rapidly downstream. Since suspended sediment transport through river confluences and bifurcation movement is poorly understood, it is assumed that the sediment moves at approximately the average channel velocity during periods of high sediment load movement. Calibration of the flow model is discussed, with an emphasis on the incorporation of cross-section data, that are not referenced to a datum, using a continuous water surface profile. Various flow regimes are examined for the Mackenzie and the Slave River Deltas in the Northwest Territories, Canada, and a significant variation in travel times is illustrated. One set of continuous daily sediment measurements throughout the Mackenzie Delta is used to demonstrate that the travel time estimates are reasonable. Keywords: suspended sediment; multi-channel river systems; flow modelling; sediment transport</p
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.
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
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