1210.1574
Detection of a virial shock around the Coma galaxy cluster
Keschet, Kushnir, Loeb, Waxman
Clusters are thought to grow by accreting mass from their surroundings through large-scale virial shocks. This should appear as gamma-ray, hard X-ray, and radio ring, elongated twoards the large-scale filmanets feeding the cluster, coincident with a cutoff in the thermal SZ signal. Report the discovery of ~5Mpc diameter gamma-ray ring around Coma, elongated towards the large scale filament connecting Coma and Abell 1367. The gamma-ray ring correlates both with a synchrotron signal and with the SZ cutoff. Signatures agree with analytic and numerical predictions, if shock deposits a few percent of the thermal energy in relativistic electrons over a Hubble time, and ~1% of the energy in B-fields. The implied inverse-Compton and synchrotron cumulative emission from similar shocks dominates the diffuse extragalactic gamma-ray and low frequency radio backgrounds. Results reveal the prolate structure of the hot gas in Coma, the feeding pattern of the cluster, and properties of the surrounding large scale voids and filaments. The anticipated detection of such shocks around other clusters would provide a powerful new cosmological probe [of what?].
1210.1576
Cosmic emulation: the concentration-mass relation for wCDM universes
Kwan, Bhattacharya, Heitmann, Habib
A cosmic emulator fo the c-M relation as a function of cosmological parameters for wCDM models, constructed from 37 individual models, with 3 nested N-body gravity-only simulations carried out for each model. Mass range: 2e12 Msun < M <1e15 Msun, with 0<z<1. Concentration varies from 2 to 8, distribution at fixed mass is Gaussian (sigma of ~1/3 of mean), almost independent of cosmology, mass and redshift over the ranges probed by the simulations. Compare results from emulator with previous analytic fits for c-M relation, and find that they underestimate the halo concentration at high masses. Sigma8 and omega_m influence the c-M relation considerably, and w has a substantial effect as well. Concentration of lower-mass haloes is more sensitive to changes in cosmological parameters are compared to cluster mass haloes.
1210.1644
The 3.3 micron PAH emission as a star formation rate indicator
Kim, et al
PAH emission features dominate the MIR spectra of SF galaxies, can be used to calibrate SFR and diagnise ionized stats of grains. The 3.3 micron PAH feature not studied as much as other PAH features, since it is weaker than others and reside outside of Spitzer capability. Use AKARI, compare sample with literature samples. Low res spectra of 20 flux-limited galaxies with mixed SED classes, 3/20 galaxies has 3.3 micron detection, which correlate with the IR luminosities of SF galaxies, but with larger scatter (1.5 dex). Correlation breaks down at the domain of ULIRGs.
1210.1802
High resolution studies of massive primordial haloes
Latif, Schleicher, Schmidt, Niemeyer
Atomic cooling haloes with T_vir > 1e4 K are the most plausible sites for the formation of the first galaxies. Study the implications of gravity driven turbulence in protogalactic haloes. High-res cosmological simulations using AMR Enzo with subgrid-scale turbulence model to study the role of unresolved turbulence. Even the highest resolution employed provides no convergence. Taking into account unresolved turbulence significantly influeneces the morphology of a halo; quantify the properties of the high-density clumps in the halo These clumps are gravitationally unbound with T>6000K and densities of 1e-12 g/cm^3. The clumps with SGS turbulence are denser and more massive compared with their counterparts in the standard simulation setup that ignores unresolved turbulence.
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