Day 623

Tuesday.
1404.1372
The dynamics and star-forming potential of the massive galactic centre cloud G0.253+0.016
Johnston et al

The massive IR dark cloud projected 45pc from the Galactic centre contains ~1e5 Msun of dense gas whilst being mostly devoid of observed SF tracers.  To scrutinize the physical properties, dynamics and structure of this cloud with reference to its SF potential, carry out a concerted SMA and IRAM 30m study of this cloud in dust continuum, CO isotopologues, shock tracing molecules, as well as H2CO to trace the gas temperature.  Detect and characterize the dust cores within G0.253+0.016 at ~1.3mm and find that the kinetic temperature of the gas is >320K on size-scales of ~0.15 pc.  Analysis of the position-velocity diagrams of observed lines show broad line widths and strong shock emission in the south of the cloud, indicating that the cloud is colliding with another cloud at v(LSR)~70 km/s.  Confirm via an analysis of the observed dynamics in the CMZ that it is an elongated structure orientated with Sgr B2 closer to the Sun, however the results suggest that the actual geometry may be more complex than an elliptical ring.  Find that the column density PDF of G0.253+0.016 is log-normal with no discernible power-law tail, consistent with little star formation, and that its width can be explained in the framework of theory predicting the density structure of clouds created by supersonic, magnetized turbulence.  Present the delta-variance spectrum of this region, and show that it is consistent with that expected for clouds with no star formation.  Using G0.253+0.016 as a test-bed of the conditions required for SF in a different physical environment to that of nearby clouds, also conclude that there is not one column density threshold for SF, but instead this value is dependent on the local physical conditions.

1404.1375
CLASH: weak-lensing shear-and-magnification analysis of 20 galaxy clusters
Umetsu et al

Present a joint shear-and-magnification WL analysis of a sample of 16 X-ray regular and 4 high-magnification galaxy clusters at 0.19<z<0.69 selected from CLASH.  Analysis uses wide-field multi-color imaging, taken primarily with Suprime-cam on Subaru.  From a stacked shear-only analysis of the X-ray selected subsample, detect the ensemble-averaged lensing signal with a total signal-to-noise ratio of ~25 in the radial range of 200 to 3500 kpc/h.  The stacked tangential-shear signal is well described by a family of standard density profiles predicted for DM-dominated halos in gravitational equilibrium, namely the NFW, truncated variants of NFW, and Einasto models.  For the NFW model, measure a mean concentration of c_200c=4.0 at M_200c=1.3e15Msun.  Show this is in excellent agreement with LCDM predictions when the CLASH X-ray selection function and projection effects are taken into account.  The best-fit Einasto shape parameter is alpha_E=0.191, which is consistent with the NFW-equivalent Einasto parameter of ~0.18.  Reconstruct projected mass density profiles of all CLASH clusters from a joint likelihood analysis of shear-and-magnification data, and measure cluster masses at several characteristic radii assuming an NFW density profile.  Also derive an ensemble-averaged total projected mass profile of the X-ray selected subsample by stacking their individual mass profiles.  The stacked total mass profile, constrained by the shear+magnification data, is shown to be consistent with the shear-based halo-model predictions including the effects of surrounding large-scale structure as a two-halo term, establishing further consistency in the context of the LCDM model.

1404.1376
CLASH: the concentration-mass relation of galaxy clusters
Merten et al

A new determination of the c-M relation for galaxy clusters based on comprehensive lensing analysis of 19 X-ray selected closers from CLASH.  Sample spans 0.19<z<0.89.  Combine WL from HST and from ground-based whide field data with SL constraints from HST.  THe result are reconstructions of the surface-mass density for all CLASH clusters on multi-scale grids.  Derivation of NFW parameters yields virial masses between 0.53e15 and 1.76e15 Msun/h and the halo concentrations are distributed around c_200c~3.7 with a 1-sigma significant negative trend with cluster mass.  Find an excellent 4% agreement between measured concentrations and the expectation from numerical simulations after accounting for the CLASH selection function based on X-ray morphology.  The simulations are analyzed in 2d to account for possible biases in the lensing reconstructions due to projection effects.  The theoretical c-M relation from X-ray selected set of simulated clusters and the c-M relation derived directly from the CLASH data free at the 90% CL.

1404.1384
The MUSIC of CLASH: predictions on the concentration-mass relation
Meneghetti, et al

Results of a numerical study based on the analysis of the MUSIC-2 simulations, aimed at estimating the expected c-M relation for CLASH.  Study nearly 1400 halos simulated at high spatial and mass resolution, projected along many LoS each.  Study the shape of both their density and surface-density profiles and fit them with a variety of radial functions, including the NFW, the generalized NFW, and the Einasto density profiles.  Derive concentrations and masses from these fits and investigate their distributions as a function of z and halo relaxation.  Use the X-ray image simulator X-MAS to produce simulated Chandra observations of the halos and use them to identify objects resembling the X-ray morphologies and masses of the clusters in the CLASH X-ray selected sample.  Also derive a c-M relation for SL clusters.  Find that the sample of simulated haloes which resemble of X-ray morphology of the CLASH clusters is composed mainly by relaxed haloes, but it also contains a significant fraction of un-relaxed systems.  For such a sample, measure an average 2d concentration which is ~11% higher than found for the full sample of simulated haloes.  After accounting for projection and select effects, the average NFW concentrations of CLASH clusters are expected to be intermediate between those predicted in 3d for relaxed and super-relaxed haloes.  Matching the simulations to the individual CLASH clusters on the basis of the X-ray morphology, expect that the NFW concentrations recovered from the lensing analysis of the CLASH clusters are in the range [3-6], with and average value of 3.87 and a standard deviation of 0.61.  Simulated haloes with X-ray morphologies similar to those of the CLASH clusters are affected by a modest orientation bias.

1404.1593
The GREAT3 challenge
Miyatake, Mandelbaum, Rowe for GREAT3 collaboration

It is an image analysis competition that aims to test algorithms to measure WL from astronomical images.  Start: 2013/10, end 2014/4.  The challenge focuses on testing the impact of WL measurements of realistically complex galaxy morphologies, realistic PSF, and combination of multiple different exposures.  It includes simulated ground- and space-based data.

1404.1644
Gravitational lensing in WDM cosmologies: the cross section for giant arcs
Mahdi et al

The nature of the dark sector of the Universe remains one of the outstanding problems in modern cosmology, with the search for new observational probes guiding the development of the next generation of observational facilities.  Clues come from tension between LCDM and observations of gravitationally lensed galaxies.  PRevious studies showed that galaxy clusters in the LCDM are not strong enough to reproduce the observed number of lensed arcs.  THis work aims to constrain the WDM cosmologies by means of the lensing efficiency of galaxy clusters drown from these alternative models.  The lensing characteristics of two samples of simulated clusters in the WDM and LCDM cosmologies have been studied.  The results show that even thug the CDM clusters are more centrally concentrated and contain more substructures, the WDM clusters have slightly higher lensing efficiency than their CDM counterparts.  The key difference is that WDM clusters have more extended and more massive sub haloes than CDM analogues.  These massive substructures significantly stretch the critical lines and caustics and hence they boost the lensing efficiency of the host halo.  Despite the increase in the lensing efficiency due to the contribution of massive substructures in the WDM clusters, this is not enough to resolve the arc statistic problem.

1404.1650
Hierarchical formation of dark matter haloes and the free streaming scale
Ishiyama

The smallest DM haloes are formed first in the early universe.  According to recent studies, the central density cusp is much steeper in these haloes than in larger haloes and scales as rho propto r^{-(1.5~1.3)}.  Present results of very large cosmological N-body simulations of the hierarchical formation and evolution of haloes over a wide mass range, beginning from the formation of the smallest haloes.  Confirmed early studies that the inner density cusps are steeper in haloes at the free streaming scale.  The cusps slope gradually becomes shallower as the halos mass increases.  The slope of haloes 50x more massive than the smallest halo is approximately -1.3.  No strong correlation exists between inner slope and the collapse epoch.  The cusp slope of haloes above the free streaming scale seems to be reduced primarily due to major merger processes.  The concentration, estimated at the present universe, is predicted to be 60-70, consistent with theoretical models and earlier simulations, and ruling out simple power law mass-concentraion relations.  Microhaloes could still exist in the present universe with the same steep density profiles.

1404.1834
Lensing measurements of the mass distribution in SDSS voids
Clampitt, Jain

Measure WL profiles of voids from LRGs in SDSS.  Find voids using an algorithm designed to maximize the lensing signal by dividing the survey volume into 2d slices, and then finding holes in the 2d distribution of LRGs.  Perform a stacked shear measurement on about 20k voids with radii between 15-40 Mpc/h and 0.16<z<0.37.  Detect the characteristic radial shear signal of voids with a statistical significance >13 sigma.  The mass profile corresponds to a fractional under density of about -0.4 inside the void radius and a slow approach to the mean density indicating a partially compensated void structure.  Compare measured shape and amplitude with the predictions of Krause+2013.  Voids in the galaxy distribution have been extensively modeled using simulations and measured in the SDSS.  Discuss how the addition of void mass profiles can enable studies of galaxy formation and cosmology.