ABSTRACT The mass distribution in massive elliptical galaxies encodes their evolutionary history, thus providing an avenue to constrain the baryonic astrophysics in their evolution. The power-law ...assumption for the radial mass profile in ellipticals has been sufficient to describe several observables to the noise level, including strong lensing and stellar dynamics. In this paper, we quantitatively constrained any deviation, or the lack thereof, from the power-law mass profile in massive ellipticals through joint lensing–dynamics analysis of a large statistical sample with 77 galaxy–galaxy lens systems. We performed an improved and uniform lens modelling of these systems from archival Hubble Space Telescope imaging using the automated lens modelling pipeline dolphin. We combined the lens model posteriors with the stellar dynamics to constrain the deviation from the power law after accounting for the line-of-sight lensing effects, a first for analyses on galaxy–galaxy lenses. We find that the Sloan Lens ACS Survey lens galaxies with a mean redshift of 0.2 are consistent with the power-law profile within 1.1σ (2.8σ) and the Strong Lensing Legacy Survey lens galaxies with a mean redshift of 0.6 are consistent within 0.8σ (2.1σ), for a spatially constant (Osipkov–Merritt) stellar anisotropy profile. We adopted the spatially constant anisotropy profile as our baseline choice based on previous dynamical observables of local ellipticals. However, spatially resolved stellar kinematics of lens galaxies are necessary to differentiate between the two anisotropy models. Future studies will use our lens models to constrain the mass distribution individually in the dark matter and baryonic components.
We report on the serendipitous discovery of the brightest Lyman break galaxy (LBG) currently known, a galaxy at z = 2.73 that is being strongly lensed by the z =0.38 luminous red galaxy (LRG) SDSS ...J002240.91+143110.4. The arc of this gravitational lens system, which we have dubbed the "8 o'clock arc" due to its time of discovery, was initially Identified in the imaging data of the Sloan Digital Sky Survey Data Release 4; followup observations on the Astrophysical Research Consortium (ARC) 3.5 m telescope at Apache Point Observatory confirmed the lensing nature of this system and led to the identification of the arc's spectrum as that of an LBG. The arc has a spectrum and a redshift remarkably similar to those of the previous record-holder for brightest LBG (MS 1512-cB58, also known as cB58), but, with an estimated total magnitude of (g.r.i) = (20.0, 19.2, 19.0) and surface brightness of ( mu sub(g), mu sub(r), mu sub(i)) = (23.3, 22.5, 22.3) mag arcsec super(-2), the 8 o'clock arc is thrice as bright. The 8 o'clock arc, which consists of three lensed images of the LBG, is 162 degree (9.6 double prime ) long and has a length-to-width ratio of 6:1. A fourth image of the LBG--a counterimage--can also be identified in the ARC 3.5 m g-band images. A simple lens model for the system assuming a singular isothermal ellipsoid yields an Einstein radius of theta unk = 3.32" plus or minus 0.16 double prime , a total mass for the lensing LRG (within the 12.1 plus or minus 0.0h super(-1) kpc enclosed by the Einstein radius) of 1.35 x 10 super(12)h super(-1) M sub( )unk, and a magnification factor for the LBG of 12.3 sub(-3.0). The LBG itself is intrinsically quite luminous unk and shows indications of massive recent star formation, perhaps as high as 160h super(-1) M sub( )unkyr super(-1).
We report the discovery of four very bright, strongly lensed galaxies found via systematic searches for arcs in Sloan Digital Sky Survey Data Release 5 and 6. These were followed up with spectroscopy ...and imaging data from the Astrophysical Research Consortium 3.5 m telescope at Apache Point Observatory and found to have redshift z > 2.0. With isophotal magnitudes r = 19.2-20.4 and 3'' diameter magnitudes r = 20.0-20.6, these systems are some of the brightest and highest surface brightness lensed galaxies known in this redshift range. In addition to the magnitudes and redshifts, we present estimates of the Einstein radii, which range from 50 to 127, and use those to derive the enclosed masses of the lensing galaxies.
We describe 10 strong lensing galaxy clusters of redshift 0.26 < or =, slant z < or =, slant 0.56 that were found in the Sloan Digital Sky Survey. We present measurements of richness (N sub(200)), ...mass (M sub(200)), and velocity dispersion for the clusters. We find that in order to use the mass-richness relation from Johnston et al., which was established at mean redshift of 0.25, it is necessary to scale measured richness values up by 1.47. Using this scaling, we find richness values for these clusters to be in the range of 22 < or =, slant N sub(200) < or =, slant 317 and mass values to be in the range of 1 x 10 super(14)/h super(-1) M sub(middot in circle) < or =, slant M sub(200) < or =, slant 30 x 10 super(14) h super(-1) M sub(middot in circle). We also present measurements of Einstein radius, mass, and velocity dispersion for the lensing systems. The Einstein radii (thetaE) are all relatively small, with 5".4 < or =, slant thetaE < or =, slant 13". Finally, we consider if there is evidence that our clusters are more concentrated than LambdaCDM would predict. We find that six of our clusters do not show evidence of overconcentration, while four of our clusters do. We note a correlation between overconcentration and mass, as the four clusters showing evidence of overconcentration are all lower-mass clusters. For the four lowest mass clusters the average value of the concentration parameter c sub(200) is 11.6, while for the six higher-mass clusters the average value of c sub(200) is 4.4. LambdaCDM would place c sub(200) between 3.4 and 5.7.
We present new results of our program to systematically search for strongly lensed galaxies in the Sloan Digital Sky Survey (SDSS) imaging data. In this study six strong lens systems are presented ...which we have confirmed with follow-up spectroscopy and imaging using the 3.5 m telescope at the Apache Point Observatory. Preliminary mass models indicate that the lenses are group-scale systems with velocity dispersions ranging from 464 to 882 km s-1 at z = 0.17 - 0.45 which are strongly lensing source galaxies at z = 0.4 - 1.4. Galaxy groups are a relatively new mass scale just beginning to be probed with strong lensing. Our sample of lenses roughly doubles the confirmed number of group-scale lenses in the SDSS and complements ongoing strong lens searches in other imaging surveys. As our arcs were discovered in the SDSS imaging data they are all bright (r 22), making them ideally suited for detailed follow-up studies.
We report the discovery of seven new, very bright gravitational lens systems from our ongoing gravitational lens search, the Sloan Bright Arcs Survey (SBAS). Two of the systems are confirmed to have ...high source redshifts z = 2.19 and z = 2.94. Three other systems lie at intermediate redshift with z = 1.33, 1.82, 1.93 and two systems are at low redshift z = 0.6,0.86. The lensed source galaxies in all of these systems are bright, with i-band magnitudes ranging from 19.73 to 22.06. We present the spectrum of each of the source galaxies in these systems along with estimates of the Einstein radius for each system. The foreground lens in most systems is identified by a red sequence based cluster finder as a galaxy group; one system is identified as a moderately rich cluster. In total, SBAS has now discovered 19 strong lens systems in the SDSS imaging data, 8 of which are among the highest surface brightness z 2-3 galaxies known.
We present the discovery and preliminary characterization of a gravitationally lensed quasar with a source redshift z sub( s) = 2.74 and image separation of 2.9 arcsec lensed by a foreground z sub( ...l) = 0.40 elliptical galaxy. Since optical observations of gravitationally lensed quasars show the lens system as a superposition of multiple point sources and a foreground lensing galaxy, we have developed a morphology-independent multi-wavelength approach to the photometric selection of lensed quasar candidates based on Gaussian Mixture Models (GMM) supervised machine learning. Using this technique and gi multicolour photometric observations from the Dark Energy Survey (DES), near-IR JK photometry from the VISTA Hemisphere Survey (VHS) and WISE mid-IR photometry, we have identified a candidate system with two catalogue components with i sub( AB) = 18.61 and i sub( AB) = 20.44 comprising an elliptical galaxy and two blue point sources. Spectroscopic follow-up with NTT and the use of an archival AAT spectrum show that the point sources can be identified as a lensed quasar with an emission line redshift of z = 2.739 plus or minus 0.003 and a foreground early-type galaxy with z = 0.400 plus or minus 0.002. We model the system as a single isothermal ellipsoid and find the Einstein radius thetas sub( E) ~ 1.47 arcsec, enclosed mass M sub( enc) ~ 4 x 10 super( 11) M... and a time delay of ~52 d. The relatively wide separation, month scale time delay duration and high redshift make this an ideal system for constraining the expansion rate beyond a redshift of 1. (ProQuest: ... denotes formulae/symbols omitted.)
Time-delay cosmography is a powerful technique to constrain cosmological parameters, particularly the Hubble constant ($H_ $). The TDCOSMO collaboration is performing an ongoing analysis of lensed ...quasars to constrain cosmology using this method. In this work, we obtain constraints from the lensed quasar using new time-delay measurements and previous mass models by TDCOSMO. This is the first TDCOSMO lens to incorporate multiple lens modeling codes and the full time-delay covariance matrix into the cosmological inference. The models are fixed before the time delay is measured, and the analysis is performed blinded with respect to the cosmological parameters to prevent unconscious experimenter bias. We obtain $ Gpc using two families of mass models, a power-law describing the total mass distribution, and a composite model of baryons and dark matter, although the composite model is disfavored due to kinematics constraints. In a flat cosmology, we constrain the Hubble constant to be The dominant source of uncertainty comes from the time delays, due to the low variability of the quasar. Future long-term monitoring, especially in the era of the Vera C. Rubin Observatory's Legacy Survey of Space and Time, could catch stronger quasar variability and further reduce the uncertainties. This system will be incorporated into an upcoming hierarchical analysis of the entire TDCOSMO sample, and improved time delays and spatially-resolved stellar kinematics could strengthen the constraints from this system in the future.
Abstract
Imaging data is the principal observable required to use galaxy-scale strong lensing in a multitude of applications in extragalactic astrophysics and cosmology. In this paper, we develop ...Lensing Exposure Time Calculator (L
ensing
ETC;
https://github.com/ajshajib/LensingETC
) to optimize the efficiency of telescope-time usage when planning multifilter imaging campaigns for galaxy-scale strong lenses. This tool simulates realistic data tailored to specified instrument characteristics and then automatically models them to assess the power of the data in constraining lens model parameters. We demonstrate a use case of this tool by optimizing a two-filter observing strategy (in the IR and ultraviolet-visual (UVIS)) within the limited exposure time per system allowed by a Hubble Space Telescope (HST) Snapshot program. We find that higher resolution is more advantageous to gain constraining power on the lensing observables, when there is a trade-off between signal-to-noise ratio and resolution; for example, between the UVIS and IR filters of the HST. We also find that, whereas a point-spread function (PSF) with sub-Nyquist sampling allows the sample mean for a model parameter to be robustly recovered for both galaxy–galaxy and point-source lensing systems, a sub-Nyquist-sampled PSF introduces a larger scatter than a Nyquist-sampled one in the deviation from the ground truth for point-source lens systems.
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