The mass distribution of a moderate redshift galaxy group and brightest group galaxy from gravitational lensing and kinematics

Abstract

The gravitational lens system CLASS B2108+213 has two radio-loud lensed images separated by 4.56 arcsec. The relatively large image separation implies that the lensing is caused by a group of galaxies. In this paper, new optical imaging and spectroscopic data for the lensing galaxies of B2108+213 and the surrounding field galaxies are presented. These data are used to investigate the mass and composition of the lensing structure. The redshift and stellar velocity dispersion of the main lensing galaxy (G1) are found to be z = 0.3648 +/- 0.0002 and sigma_v = 325 +/- 25 km/s, respectively. The optical spectrum of the lensed quasar shows no obvious emission or absorption features and is consistent with a BL Lac type radio source. However, the tentative detection of the G-band and Mg-b absorption lines, and a break in the spectrum of the host galaxy of the lensed quasar gives a likely source redshift of z = 0.67. Spectroscopy of the field around B2108+213 finds 51 galaxies at a similar redshift to G1, thus confirming that there is a much larger structure at z ~ 0.365 associated with this system. The width of the group velocity distribution is 694 +/- 93 km/s, but is non-Gaussian, implying that the structure is not yet viralized. The main lensing galaxy is also the brightest group member and has a surface brightness profile consistent with a typical cD galaxy. A lensing and dynamics analysis of the mass distribution, which also includes the newly found group members, finds that the logarithmic slope of the mass density profile is on average isothermal inside the Einstein radius, but steeper at the location of the Einstein radius. This apparent change in slope can be accounted for if an external convergence gradient, representing the underlying parent halo of the galaxy group, is included in the mass model.

18 pages, 14 figures, 5 tables, accepted for publication in MNRAS

References in corpus (29)

• A direct empirical proof of the existence of dark matter
• Galaxy Groups in the SDSS DR4: I. The Catalogue and Basic Properties
• A constant dark matter halo surface density in galaxies
• The Structure & Dynamics of Massive Early-type Galaxies: On Homology, Isothermality and Isotropy inside one Effective Radius
• Detection of a Dark Substructure through Gravitational Imaging
• Bayesian Strong Gravitational-Lens Modeling on Adaptive Grids: Objective Detection of Mass Substructure in Galaxies
• Strong and weak lensing united III: Measuring the mass distribution of the merging galaxy cluster 1E0657-56
• Revealing the properties of dark matter in the merging cluster MACSJ0025.4-1222
• Density profiles of galaxy groups and clusters from SDSS galaxy-galaxy weak lensing
• The luminosities, sizes and velocity dispersions of Brightest Cluster Galaxies: Implications for formation history
• Separating baryons and dark matter in cluster cores: a full 2-D lensing and dynamic analysis of Abell 383 and MS2137-23
• Two-dimensional kinematics of SLACS lenses: II. Combined lensing and dynamics analysis of early-type galaxies at z = 0.08 - 0.33
• High resolution imaging of the anomalous flux-ratio gravitational lens system CLASS B2045+265: Dark or luminous satellites?
• The survival of dark matter halos in the cluster Cl0024+16
• The Baryon Fractions and Mass-to-Light Ratios of Early-Type Galaxies
• The role of luminous substructure in the gravitational lens system MG 2016+112
• Two-dimensional kinematics of SLACS lenses: I. Phase-space analysis of the early-type galaxy SDSS J2321-097 at z=0.1
• Probing the truncation of galaxy dark matter halos in high density environments from hydrodynamical N-body simulations
• The Gravitational Lens -- Galaxy Group Connection. II. Groups Associated with B2319+051 and B1600+434
• X-ray Properties of Intermediate-Redshift Groups of Galaxies
• The sizes of galaxy halos in galaxy cluster Abell 1689
• Detection of a Companion Lens Galaxy using the Mid-infrared Flux Ratios of the Gravitationally Lensed Quasar H1413+117
• Lens Galaxy Properties of SBS1520+530: Insights from Keck Spectroscopy and AO Imaging
• The Sloan Bright Arcs Survey : Six Strongly Lensed Galaxies at z=0.4-1.4
• Two strong-lensing clusters confront universal dark-matter profiles
• Free-free absorption in the gravitational lens JVAS B0218+357
• Probing a massive radio galaxy with gravitational lensing
• Steepened inner density profiles of group galaxies via interactions: An N-body analysis
• The X-ray Properties of Moderate-redshift Galaxy Groups Selected by Association with Gravitational Lenses

Cited by in corpus (10)

• The Sloan Lens ACS Survey. XII. Extending Strong Lensing to Lower Masses
• The Effect of Environment on Shear in Strong Gravitational Lenses
• Galaxy Number Counts and Implications for Strong Lensing
• SHARP - V. Modelling gravitationally-lensed radio arcs imaged with global VLBI observations
• J0454-0309: Evidence for a strong lensing fossil group falling into a poor galaxy cluster
• Dynamical analysis of strong-lensing galaxy groups at intermediate redshift
• Dark matter distribution in galaxy groups from combined strong lensing and dynamics analysis
• Dark matter-rich early-type galaxies in the CASSOWARY 5 strong lensing system
• The double quasar Q2138-431: detection of a lensing galaxy
• The final candidate from the JVAS/CLASS search for 6 arcsec to 15 arcsec image separation lensing