Tuesday.
1406.1799
Co-orbiting satellite galaxy structures are still in conflict with the distribution of primordial dwarf galaxies
Pawlowski, .. Kroupa, ... et al
Both major galaxies in the Local Group host planar distributions of co-orbiting satellite galaxies, the Vast Polar Structure (VPOS) of the MW and the Great Plane of Andromeda (GPoA). The LCDM cosmological model did not predict these features. However, according to 3 recent studies the properties of GPoA and the flattening of the VPOS are common features among sub-halo based LCDM satellite systems, and the GPoA can be naturally explained by satellites being acquired along cold gas streams. Point out some methodological issues in these studies: either the selection of model satellites is different from that of the observed ones, or an incomplete set of observational constraints has been considered, or the observed satellite distribution is inconsistent with basic assumptions. Once these issues have been addressed, the conclusions are different: features like the VPOS and GPoA are very rare (each with probability <1e03, and combined probability <1e-5) if satellites are selected from a LCDM simulation combined with SAM, and accretion along cold streams is no natural explanation of the GPoA. The origin of planar dwarf galaxy structures remains unexplained in the standard paradigm of galaxy formation. [Do they understand how SAM works?]
1406.1800
Toward optimal cluster power spectrum analysis
Smith, Marian
The PS of galaxy clusters is an important probe of the cosmological model. Determine the optimal weighting scheme for maximizing the signal-to-noise ratio for such measurements. Find a closed form analytic expression for the optimal weights. Expression takes into account: cluster mass, finite survey volume effects, survey masking, and a flux limit. The implementation of this weighting scheme requires knowledge of the measured cluster masses, and analytic models for the bias and space-density of clusters as a function of mass and redshift. Recent studies have suggested that theo primal method for reconstruction of the matter density field from a set of clusters is mass-weighting (Seljak+2009, Hamaus+2010, Cai+2011). Compare optimal weighting scheme with this approach and also with the original PS scheme of Feldman+1994. Show that the optimal weighting scheme outperforms these approaches for both volume- and flux-limited cluster surveys. Finally, present an expression for the Fisher information matrix for cluster PS analysis. Expressiong shows that for an optimally weighted cluster survey the cosmological information content is boosted, relative to the standard approach of Tegmark (1997).
1406.2020
Earthshine on a Young Moon: Explaining the Lunar Farside Highlands
Roy, Wright, Sigurdsson
The lunar far side highlands problem refers to the curious and unexplained fact that the far side lunar crust is thicker, on average, than the nearside crust. Recognize the crucial influence of Earthshine, and propose that it naturally explains this hemispheric dichotomy. Since the accreting Moon rapidly achieved synchronous rotation, a surface and atmospheric thermal gradient was imposed by the proximity of the hot, post-Giant-impact Earth. This gradient guided condensation of atmospheric and accreting material, preferentially depositing crust-forming refractories on the cooler far side, resulting in a primordial bulk chemical inhomogeneity that seeded the crustal asymmetry. The model provides a causal solution to the lunar highlands problem: the thermal gradient created by Earthshine produce the chemical gradient responsible for the crust thickness dichotomy that defines the lunar highlands.
1406.2037
Resolving the origin of the diffuse soft X-ray background
Smith et al
The ubiquitous diffuse soft (1/4 keV) X-ray BG emission may arise from charge exchange between solar wind ions and neutral atoms in the heliosphere, but no detailed models have been fit to the available data. Report on a new model for charge exchange in the solar wind, which when combined with a diffuse hot plasma component filling the Local Cavity provides a good fit to the only available high-resolution soft X-ray and extreme ultraviolet (EUV) spectra using plausible parameters for the solar wind. The implied hot plasma component is in pressure equilibrium with the local cloud that surrounds the solar system, creating for the first time a self-consistent picture of the local ISM.
1406.2160
Pinpointing extragalactic neutrino sources in light of recent IceCube observations
Ahlers, Halzen
The IceCube collaboration has recently reported the observation of a flux of high-energy astrophysical neutrinos. The angular distribution of events is consistent with an isotropic arrival direction of neutrinos which is expected for an extragalactic origin. Estimate the prospects of detecting individual neutrino sources from a quasi-diffuse superposition of many extragalactic sources at the level of the IceCube observation. Analysis takes into account ensemble variations for the source distribution as well as the even statistics of individual sources. Show that IceCube in its present configuration is sensitive to rare <1e-8 /Mpc^3/yr transient source classes within 5 years of operation via the observation of multiplets. Identification of time-independent sources is more challenging due to larger backgrounds. Estimate that during the same period IceCube is sensitive to sparse sources with densities of <1e-6 /Mpc^3 via association of events with the closest 100 sources of an ensemble. Show that a next-generation neutrino observatory with 5 times the effective area of IceCube and otherwise similar detector performance would increase the sensitivity to source densities and rates by about two orders of magnitude.
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