Day 745

Tuesday.

1409.3845
Scaling properties of a complete X-ray selected galaxy group sample
Lovisari, Reiprich, Schellenberger

Main goal of this work is to constrain the galaxy group scaling relations corrected for select effects, and to quantify the influence of non-graviataional physics and the low-mass regime.  Analyze XMM-Newton observations for a complete sample of galaxy groups selected from ROSAT All-Sky Survey and compare the derived scaling properties with a galaxy cluster sample.  To investigate the role played by the different non-gravitational processes, compare the observational data with the predictions of hydrodynamical simulations.  After applying the correction for selection effects, the L-M relation is steeper than the observed one.  Its slope is also steeper than the value obtained by using the more massive systems of the HIFLUGCS sample.  This behavior can be explained by a gradual change of the true L-M relation which should be taken into account when converting the observational parameters into masses.  The other observed scaling relations (not corrected for selection biases) do not show any break although the comparison with the simulations suggests that feedback processes play an important role in the formation and evolution of galaxy groups.  Thanks to the master sample of 82 objects spanning two order of magnitude in mass, tightly constrain the dependence of the gas mass fraction on the total mass, finding almost a factor of two difference between groups and clusters.

1409.3992
The rich complexity of 21-cm fluctuations produced by the first stars
Fialkov, Barkana

Explore the complete history of the 21-cm signal in z=7-40, including various epochs of cosmic evolution related to primordial SF, and should be accessible to existing or planned low-frequency radio telescopes.  Use semi-numerical computational methods to explore the fluctuation signal over wave numbers between 0.03 and 1 /Mpc, accounting for the homogeneous backgrounds of Ly-a, X-ray, Lyman-Werner and ionizing radiation.  Focus on the recently noted expectation of heating dominated by a hard X-ray spectrum from high-mass X-ray binaries.  Study the resulting delayed cosmic heating and suppression of gas temperature fluctuations, allowing for large variations in the minimum halo mass that contributes to star formation.  Show that the wave numbers at which the heating peak is detected in observations should tell us about the characteristic mean free path and spectrum of the emitted photons, thus giving key clues as to the character of the sources that heated the primordial Universe.  Also consider the LoS anisotropy, which allows additional information to be extracted from the 21-cm signal.  For example, the heating transition at which the cosmic gas is heated to the temperature of the CMB should be clearly marked by an especially isotropic PS.  More generally, an additional cross-power component Px directly probes which sources dominated 21-cm fluctuations.  In particular, during cosmic deionization (and after the just-mentioned heating transition), Px is negative on scales dominated by ionization fluctuations and positive on those dominated by temperature fluctuations.