1306.2948
The dark matter halo concentration and stellar initial mass function of a CASSOWARY group
Deason et al
Use galaxy group member dynamics with spectra (in addition to lensing and central dynamical constraints) to measure the group mass. 21 confirmed members found, calibrate an analytic tracer mass with cosmo simulations. The L weighted LoS velocity dispersion and the Einstein radius of the lens are used as mass probes in the inner regions of the galaxy. Constrain mass and concentration of DM independently, in addition to total stellar mass of the central galaxy. Find DM halo in good agreement with sims, and a stellar mass-to-light ratio which favors a Salpeter IMF. Measurement of a normal halo concentration suggests that there is no discrepancy between simulations and observations at the group mass scale. This is in contrast to the cluster mass scale for which a number of studies have claimed over-concentrated halos. [at least for this one group.] While the halo mass is robustly determined, and the halo concentration is not significantly affected by systematics, the resulting stellar mass-to-light ratio is sensitive to the choice of stellar parameters, such as density profile and velocity anisotropy.
1306.2950
UV-Continuum slopes of >4000 z~4-8 galaxies from the HUDF/XDF, XUDF09, ERS, CANDELS-South, and CANDELS-North fields
Bouwends et al
Previous studies suffer from small systematic in beta. After correction, z~4,5,6,7 galaxies is -2.03, -2.14, -2.24, and -2.33, respectively. New beta values are redder than reported in the past, but bluer than other recent results. Bluer beta's at lower luminosities, and evolution to bluer beta's at high z, confirmed. At z~7, the observed beta's suggest non-zero, but low dust extinction, and they agree well with values predicted in cosmo hydro sims.
1306.2955
The structure of cosmic voids in a LCDM universe
Ricciardelli et al
Eulerian cosmological codes are especially suited to properly describe the low density regions, excellent tools to study the formation and evolution of cosmic voids. Present results of Eulerian AMR hydro and N-body sim that has been designed to refine the computational grid in the underdense regions of the simulated volume; void regions are better described due to the combined effect of the Eulerian character of the numerical technique and the use of high numerical resolution from the AMR approach. To analyze the outcome of this simulation, construct a new void finder optimally suited to find the hierarchy of voids in AMR sims. The algorithm identifies voids starting from the cells with least density and highest velocity divergence and then expanding the underdense volume until reaching the void walls, defined from the steepness of the density gradient. At z=0, in a cosmological box of comoving side length 100 Mpc/h, identify hundreds of voids with sizes up to 17 Mpc/h and typical density contrast of ~0.8, which show a complex morphology and an intricate hierarchy of nested structures. The analysis of their mass density profile leads to the conclusion that a universal density profile can be applied to voids of any size, density, morphology and redshift.
1306.3035
Sparsely sampling the sky: regular vs random sampling
Paykari, Piers, Starck, Jaffe
Sparse sampling strategy could be a substitute for the contiguous observations; previous work showed the case for regular sparse sampling (observed patches regularly distributed on the sky). The regularity of the mask introduces a periodic patter in the window function, which induces periodic correlations at specific scales. Use the Bayesian experimental design to investigate a random sparse sampling, where the observed patches are randomly distributed over the total sparsely sampled area. Find that, as there is no preferred scale in the window function, the induced correlation is evenly distributed amongst all scales. This could be desirable if we are interested in specific scales in the galaxy power spectrum, such as BAO scales. However, for constraining the overall galaxy power spectrum and the cosmological parameters, there is no preferences over regular or random sampling. Hence any approach that is practically more suitable can be chosen and can relax the regular-grid condition for the distribution of the observed patches.
1306.3136
Galactic winds - how to launch galactic outflows in typical Lyman-break galaxies
von Glasow, Krause, Sommer-Larsen, Burkert
Hydro-sims of young galactic disc embedded in a hot gaseous halo using parameters typical for LBGs. Take into account the (static) gravitational potentials due to a DM halo, a stellar bulge and a disc of stars and gas. SF is treated by a local Kennicutt-Schmidt law. Simplify the structure of the interstellar medium by restricting the computational domain to a 25th of the full azimuthal angle, effectively assuming large-scale axisymmetry and neglecting any effects of spiral structure, and focus on the large-scale ISM drivers, the superbubbles. SNe are triggered randomly and have preset event sizes of several tens to hundreds. Further investigate different halo gas pressures and energy injection methods. Many of the simulated galaxies develop bipolar outflows. Characterise the strength of the outflow by mass and energy outflow rates, and investigate the effect of changes to the details of the model. Find that SNe are more effective if comprised into larger superbubbles . The weight and the pressure of the halo gas is able to quench galactic outflows. The wind emerges from a series of superbubbles in regions where a critical SF density is exceeded. The superbubbles expand into the gaseous halo at slightly supersonic speed, producing radiative shock waves with similar characteristics as the absorptions systems observed around LBGs.
1306.3165
On the origin and evolution of cluster scaling relations
Diemer, Kravtsov, More
Investigate whether the evolution of cluster scaling relations is affected by the spurious evolution of mass due to the evolving reference density with respect to which halo masses are defined (pseudo-evolution). Use the relation between mass, M, and velocity dispersion, sigma, as a test case, and find that the deviation from the M-sigma relation of cluster-sized haloes due to pseudo-evolution is smaller than 10% for a wide range of mass definitions. The reason for this small impact is a tight relation between the velocity dispersion and mass profiles, sigma(<r) = const * (GM(<r)/r)^(1/2), which holds across a large radial range. Show that such a relation is generically expected for a wide range of density profiles, as long as halos are in approximate Jeans equilibrium. Thus, as the outer "virial" radius used to define the halo mass, R, increases due to pseudo-evolution, haloes approximately preserve their M-sigma relation. This result explains why such relations are almost insensitive to the definition of the virial radius, and highlights the fact that tight scaling relations are the result of tight equilibrium relations between radial profiles of physical quantities, rather than a result of the virial theorem applied to the cluster as a whole within some unique boundary. Find exceptions at very small and very large radii, where the profiles deviate from the relations they exhibit at intermediate radii. Discuss the implications of these results for other cluster scaling relations, and argue that pseudo-evoltuion should have very small effects on most scaling relations, except for those which involve the stellar masses of galaxies. In particular, show that the relation between stellar mass fraction and total mass is affected by pseudo-evolution, and is largely shaped by it for halo masses smaller than 1e14 Msun.
1306.3209
Anisotropic cosmic ray diffusion and its implications for gamma ray astronomy
Giacinti, Kachelriess, Semikoz
Analysis for TeV-PeV CR diffusion around their sources usually assume either isotropic diffusion or anisotropic diffusion due to the regular Galactic B-field. Show that none of them is adequate on distances smaller than the maximal scale L_max~100pc of fluctuations in the turbulent interstellar B-field. As a result, predict anisotropic gamma-ray emissions around CR proton and electron sources, even for uniform densities of target gas. The centers of extended emission regions may have non-negligible offsets from their sources, leading to the risk of misidentifications. Gamma-rays from CR filaments have steeper energy spectra than those from surrounding regions. Point out that gamma-ray telescopes can be used in the future as a new way to probe and to deduce the parameters of the interstellar B-field.
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