Day 526

Thursday.

1310.2239
Mergers and mass accretion for infalling haloes both end well outside cluster virial radii
Behroozi, Wechsler, Lu, Hahn, Busha, Klypin, Primack

Find that infalling DM haloes (progenitors of satellite haloes) begin losing mass well outside the virial radius of their eventual host haloes.  The peak mass occurs at a range of clustercentric distances, with median and 68th percentile range of 1.8+2.3-1.0 Rvir for progenitors of z=0 satellites.  The peak circular velocity for infalling haloes occurs at significantly larger distances (3.7+3.3-2.2 Rvir at z=0).  This difference arises because different physical processes set peak circular velocity (typically ~1:5 and larger mergers which cause transient circular velocity spikes) and peak mass (typically, smooth accretion) for infalling haloes.  Find that infalling haloes also stop having significant mergers well before they enter the virial radius of their eventual hosts.  Mergers larger than a 1:40 ratio in halo mass end for infalling haloes at similar clustercentric distances (~1.9 Rvir) as the end of overall mass accretion.  However, mergers larger than 1:3 typically end for infalling haloes at more than 4 virial radial away from their eventual hosts.  This limits the ability of mergers to affect quenching and morphology changes in clusters.  Also note that the transient spikes which set peak circular velocity may lead to issues with abundance matching on that parameter, including unphysical galaxy stellar mass growth profiles near clusters; propose a simple observational test to check if a better halo proxy for galaxy stellar mass exists.
1310.2242
Thermal conduction and multiphase gas in cluster cores
Wagh, Sharma, McCourt

Examine the role of thermal conduction and magnetic fields in cores of galaxy clusters through global simulations of the ICM; study the influence of thermal conduction, both isotropic and anisotropic, on the condensation of multiphase gas in cluster cores.  Previous hydrodynamics simulations have shown that cold gas condenses out of the hot ICM in thermal balance only when the ratio of the cooling time and the free fall time is <~10.  Since thermal conduction is significant in the ICM and it suppresses local cooling at small scales, it is imperative to include thermal conduction in such studies.  Find that anisotropic (along local magnetic field lines) thermal conduction does not influence the condensation criterion for a general magnetic geometry, even if thermal conductivity is large.  However, with isotropic thermal conduction cold gas condenses only if conduction is suppressed (by a factor <~ 0.3) with respect to the Spitzer value.

1310.2243
Detecting dark matter substructures around the Milky Way
Feldmann, Spolyar

CDM predicts a large number of starless DM haloes surrounding the MW, but a clear observational evidence of these "dark" substructures remains elusive.  Here, present a detection method based on the small, but detectable, velocity changes that an orbiting substructure imposes on the stars in the MW disk.  Using high-res numerical simulations, estimate that the new space telescope Gaia should detect the kinematic signatures of a few starless substructures provided the CDM paradigm holds.  Such a measurement will provide unprecedented constraints on the primordial matter PS at low-mass scales and offer a new handle onto the particle physics properties of DM.  

1310.2251
Hubble constant and dark energy inferred from free-form determined time delay distances
Sereno, Paraficz

Time delays of multiple images of lensed sources can probe the geometry of the universe.  Propose a new method based on free-form modeling of gravitational lensing to estimate time-delay distances and, in turn, cosmological parameters.  Apply the method to 18 systems having time delay measurements and find H0=69pm6(stat)pm4(sys) km/s/Mpc.  In combination with WMAP9, the constraints on the DE are Omega_w=0.68pm0.05 and w=-0.86pm0.17 in a flat model with constant EoS.  

1310.2253
A budget and accounting of metals at z~0: results from the COS-Halos survey
Peeples, ... Prochaska, et al

Budget and accounting of metals in and around SF galaxies at z~0; use empirically derived SFHs and SNe and AGB yields and rates to estimate the total mass of metals produced by galaxies with present-day stellar mass of 1e9.3-11.6 Msun.  Show that a surprisingly constant 20-25% mass fraction of produced metals remain in galaxies' stars, interstellar gas and interstellar dust, with little dependence of this fraction on the galaxy stellar mass.  Thus, the bulk of metals are outside of galaxies, produced in the progenitors of today's L* galaxies.  From this, map the distribution of CGM metals as traced by both the highly ionized OVI ion and a suite of low-ionization species; combined with constraints on circumgalactic dust and hotter X-ray emitting gas out to similar impact parameters, show that ~40% of metals produced by M*~1e10.1 Msun galaxies can be easily accounted for out to150 kpc.  With the current data, cannot rule out a constant mass of metals within this fixed physical radius.  This census provides a crucial boundary conditions for the eventual fate of metals in galaxy evolution models.  

1310.2255
Halo-driven size and velocity dispersion evolution of early-type galaxies
Posti et al

ETGs are observed to be more compact, on average, at z>2 than at z~0, at fixed stellar mass.  Such evolution could be at least partly driven by an underlying evolution of the host DM haloes where the new galaxies form.  Explore this hypothesis by studying the distribution of halo central velocity dispersion and half-mass radius as functions of halo mass M and redshift z, in a cosmological LCDM N-body sim.  In 0<z<2.5, find sigma_0 proportional to M^0.31-0.37 and r_h proportional to M^0.28-0.32, close to the values expected for homologous virialized systems.  At fixed mass in the range 1e11 Msun<M<5.5e14 Msun, find sigma_0 proportional to (1+z)^0.35 and r_h proportional to (1+z)^-0.7.  Show that such evolution of the halo scaling laws is driven by individual haloes growing in mass following the evolutionary tracks sigma_0 proportional to M^0.2 and r_h proportional to M^0.6, consistent with simple dissipationless merging models in which the encounter orbital energy is accounted for.  Compare the N-body data with ETGs observed at 0<z<3 by populating the haloes with a stellar component under simple but justified assumptions: find that the resulting galaxies evolve consistently with the observed size evolution of ETGs up to z~2, but the model has difficulty reproducing the fast evolution observed at z>2.  Conclude that up to z~2 a substantial fraction of the size evolution of ETGs can be ascribed to that of the underlying halo population.  

1310.2295
Cluster magnification & the mass-richness relation in CFHTLenS
Ford, Hildebrandt, Van Waerbeke, Erben, Laigle, Milkeraitis, Morrison

Lensing magnification detected with 9.7 sigma significance on a large sample of galaxy clusters in CFHTLenS.  ~154 sq deg with >18k cluster candidates at 0.2<=z<=0.9, detected using 3d-matched filter cluster-finder of Milkeraitis+2010.  Fit composite-NFW models to the ensemble, accounting for cluster miscentering, source-lens redshift overlap, as well as nearby structure (the 2-halo term), and recover mass estimates of the cluster DM haloes in range of 1e13 Msun to 2e14 Msun.  Cluster richness is measured for the entire sample, and bin the clusters according to both richness and redshift.  A mass-richness relation M200=M0(N200/20)^beta is fit to the measurements.  For two different cluster miscentering models, find consistent results for the normalization and slope, M0=2.3pm0.2e13 Msun, beta=1.4pm0.1 and M)=2.2pm0.2e13Msun, beta=1.5pm0.1.  Find that accounting for the full z distribution of lenses and sources is important, since any overlap can have an impact on mass estimate inferred from flux magnification.