We present the results of a gravitational lensing analysis of the bright $zs=2.957$ sub-millimeter galaxy (SMG), HERMES J105751.1+573027 found in {it Herschel}/SPIRE Science Demonstration Phase data from the Herschel Multi-tiered Extragalactic Survey
(HerMES) project. The high resolution imaging available in optical and Near-IR channels, along with CO emission obtained with the Plateau de Bure Interferometer, allow us to precisely estimate the intrinsic source extension and hence estimate the total lensing magnification to be $mu=10.9pm 0.7$. We measure the half-light radius $R_{rm eff}$ of the source in the rest-frame Near-UV and $V$ bands that characterize the unobscured light coming from stars and find $R_{rm eff,*}= [2.0 pm 0.1]$ kpc, in good agreement with recent studies on the Submillimeter Galaxy population. This lens model is also used to estimate the size of the gas distribution ($R_{rm eff,gas}= [1.1pm0.5]$) kpc by mapping back in the source plane the CO (J=5-4) transition line emission. The lens modeling yields a relatively large Einstein radius $R_{rm Ein}= 4farcs10 pm 0farcs02$, corresponding to a deflector velocity dispersion of [$483pm 16] ,kms$. This shows that HERMES J105751.1+573027 is lensed by a {it galaxy group-size} dark matter halo at redshift $zlsim 0.6$. The projected dark matter contribution largely dominates the mass budget within the Einstein radius with $f_{rm dm}(<R_{rm Ein})sim 80%$. This fraction reduces to $f_{rm dm}(<R_{rm eff,G1}simeq 4.5kpc)sim 47%$ within the effective radius of the main deflecting galaxy of stellar mass $M_{rm *,G1}=[8.5pm 1.6] times 10^{11}msun$. At this smaller scale the dark matter fraction is consistent with results already found for massive lensing ellipticals at $zsim0.2$ from the SLACS survey.
We use stellar dynamics, strong lensing, stellar population synthesis models, and weak lensing shear measurements to constrain the dark matter (DM) profile and stellar mass in a sample of 53 massive early-type galaxies. We explore three DM halo model
s (unperturbed Navarro Frenk & White [NFW] halos and the adiabatic contraction models of Blumenthal and Gnedin) and impose a model for the relationship between the stellar and virial mass (i.e., a relationship for the star-formation efficiency as a function of halo mass). We show that, given our model assumptions, the data clearly prefer a Salpeter-like initial mass function (IMF) over a lighter IMF (e.g., Chabrier or Kroupa), irrespective of the choice of DM halo. In addition, we find that the data prefer at most a moderate amount of adiabatic contraction (Blumenthal adiabatic contraction is strongly disfavored) and are only consistent with no adiabatic contraction (i.e., a NFW halo) if a mass-dependent IMF is assumed, in the sense of a more massive normalization of the IMF for more massive halos.
The existence of strong lensing systems with Einstein radii (Re) covering the full mass spectrum, from ~1-2 (produced by galaxy scale dark matter haloes) to >10 (produced by galaxy cluster scale haloes) have long been predicted. Many lenses with Re a
round 1-2 and above 10 have been reported but very few in between. In this article, we present a sample of 13 strong lensing systems with Re in the range 3- 8, i.e. systems produced by galaxy group scale dark matter haloes, spanning a redshift range from 0.3 to 0.8. This opens a new window of exploration in the mass spectrum, around 10^{13}- 10^{14} M_{sun}, which is a crucial range for understanding the transition between galaxies and galaxy clusters. Our analysis is based on multi-colour CFHTLS images complemented with HST imaging and ground based spectroscopy. Large scale properties are derived from both the light distribution of the elliptical galaxies group members and weak lensing of the faint background galaxy population. On small scales, the strong lensing analysis yields Einstein radii between 2.5 and 8. On larger scales, the strong lenses coincide with the peak of the light distribution, suggesting that mass is traced by light. Most of the luminosity maps have complicated shapes, indicating that these intermediate mass structures are dynamically young. Fitting the reduced shear with a Singular Isothermal Sphere, we find sigma ~ 500 km/s and an upper limit of ~900 km/s for the whole sample. The mass to light ratio for the sample is found to be M/L_i ~ 250 (solar units, corrected for evolution), with an upper limit of 500. This can be compared to mass to light ratios of small groups (with sigma ~ 300 km/s and galaxy clusters with sigma > 1000 km/s, thus bridging the gap between these mass scales.
We study the relation between the internal structure of early-type galaxies and their environment using 70 strong gravitational lenses from the Sloan ACS Lens Survey. The Sloan database is used to determine two measures of overdensity of galaxies aro
und each lens: the projected number density of galaxies inside the tenth nearest neighbor (Sigma_{10}) and within a cone of radius one h^{-1} Mpc (D_1). Our main results are: 1) The average overdensity is somewhat larger than unity, consistent with lenses preferring overdense environments as expected for massive early-type galaxies (12/70 lenses are in known groups/clusters). 2) The distribution of overdensities is indistinguishable from that of twin non-lens galaxies selected from SDSS to have the same redshift and stellar velocity dispersion sigma_*. Thus, within our errors, lens galaxies are an unbiased population, and the SLACS results can be generalized to the overall population of early-type galaxies. 3) Typical contributions from external mass distribution are no more than a few per cent, reaching 10-20% (~0.05-0.10 external convergence) only in the most extreme overdensities. 4) No significant correlation between overdensity and slope of the mass density profile of the lens is found. 5) Satellite galaxies (those with a more luminous companion) have marginally steeper mass density profiles than central galaxies (those without). This result suggests that tidal stripping may affect the mass structure of early-type galaxies down to kpc scales probed by strong lensing, when they fall into larger structures [ABRIDGED].
We have then searched for preferential orientations of faint galaxies in the Coma cluster (down I_Vega~-11.5). By applying a deconvolution method to deep u* and I band images of the Coma cluster, we were able to recover orientations down to faint mag
nitudes. No preferential orientations are found in more than 95% of the cluster, and the brighter the galaxies, the fewer preferential orientations. The minor axes of late type galaxies are radially oriented along a northeast -southwest direction and are oriented north-south in the western X-ray sub- structures. For early type galaxies, in the western regions showing significant preferential orientations, galaxy major axes are oriented perpendicularly to the north-south direction. In the eastern significant region and close to NGC 4889, galaxy major axes also point toward the 2 cluster dominant galaxies. In the southern significant regions, galaxy planes are tangential with respect to the clustercentric direction, except close to (alpha=194.8, delta=27.65) where the orientation is close to -15deg. Part of the orientations of the minor axes of late type galaxies and of the major axes of early type galaxies can be explained by a tidal torque model applied to cosmological filaments and local merging directions. Another part (close to NGC4889) can be accounted for by collimated infalls. For early type galaxies, the (alpha=194.8, delta=27.65) region shows orientations that probably result from processes involving induced star formation.
