Saturday. Will go running to the church, then in the afternoon go to the Art Exhibition Hall of the Federal Republic of Germany (Kunst- und Ausstellungshalle der Bundesrepublik Deutschland) to see the Anime as an Art Form exhibition. I think I'm slightly depressed. The sun is out today, so I hope that and exercise would help.
1109.1281
Moving mesh cosmology: numerical techniques and global statistics
Vogelsberger, Sijacki, Keres, Springel, Hernquist
Compare AREPO with GADGET. Both use identical Tree-PM gravity solver and same sub-resolution physics for the treatment of star formation, but employ a completely different method to solve the inviscid Euler equations; allows clean assessment of the impact of hydro-solver uncertainties on galaxy formation simulation studies. Prediction for global baryon statistics (cosmic SF rate density). Properties of individual galaxies and haloes examined by Keres+, while Sijacki+ uses idealised simulations to analyse differences between the hydro schemes. Global baryon statistics differ significantly between the two simulation approaches. AREPO shows higher SFR at late teims, lower mean temperatures, and different gas mass fractions in characteristic phases of the intergalacitic medium, in particular a reduced amount of hot gas. Differences originate through a higher heating rate with SPH in the outer parts of haloes, caused by viscous dissipation of SPH's inherent sonic velocity noise and SPH's efficient damping of subsonic turbulence injected in the halo infall region, and because of a higher efficiency of gas stripping in AREPO. These differences also produce more disk-like galaxy morphologies in the moving mesh calculations compared to SPH. Our results hence demonstrate that inacccuracies in hydrodynamic solvers can lead to comparatively large systematic differences even at the level of predictions for the global state of baryons.
* I guess they're implying that GADGET is less accurate in its hydrodynamic solvers.
1109.1285
Turbulent pressure support in the outer parts of galaxy clusters
Parrish, McCourt, Quataert, Sharma
Study turbulence due to the magnetothermal instability (MTI) in the interacluster medium (ICM) of galaxy clusters, with 3d MHD simulations with anisotropic thermal conduction. The MTI grows on timescales of ~1 Gyr and is capable of driving vigorous, sustained turbulence in the outer parts of galaxy clusters if temperature gradient is maintained despite the rapid thermal conduction. If so, MTI turbulence can provide up to 5-30% of the pressure support beyond r_500 in galaxy clusters. The turbulence driven by the MTI is generally additive to other sources of turbulence in the ICM, such as that produced by structure formation. This new source of non-thermal pressure support reduces the observed SZ signal and X-ray pressure gradient for a given cluster mass and introduces a cluster mass and temperature gradient-dependent bias in SZ and X-ray mass estimates of clusters. This additional physics may also need to be taken into account when estimating the matter power spectrum normalization, sigma-8, through simulation templates from the observed amplitude of the SZ power spectrum.
1109.1288
Do baryons alter the halos of low surface brightness galaxies?
de Naray, Spekkens
Simulations show that small haloes that host low surface brightness (LSB) galaxies should be triaxial, centrally-concentrated cuspy haloes, but the observations show these galaxies reside in round, roughly constant density cored haloes. What are the processes that alter the shape and density structure of the inner halo? Study plausibility that a previously higher baryonic mass content and feedback from SF can modify DM haloes of these galaxies. Compare to properties of bulgeless disk galaxies formed in simulations of LSB galaxy sample. Find: observational constraints on LSB galaxy SF histories, structure, and kinematics make it difficult for baryonic physics to sphericalize and decrease the central density of the DM haloes of LSB galaxies.
1109.1492
The galactic O-star spectroscopic (GOSSS) and northern massive dim stars (NoMaDS) surveys, the Galactic O-star catalog (GOSC), and Marxist Ghost Buster (MGB)
Apellaniz, et al
Several ongoing massive-star (mostly of spectral type O) surveys that are significantly increasing the quality and quantity of the spectroscopic information about these objects.
1109.1522
Improved models for cosmic infrared background anisotropies: New constraints on the IR galaxy population
Shang, Haiman, Knox, Oh
CIB anisotropies sensitive to the connection between SF and DM haloes over the entire cosmic SF history. Model that associates SF galaxies with DM haloes and subhaloes; parameterized relation between dust-processed IR luminosity and (sub)halo mass. With 3 params, can simultaneously fit the 4 frequence bands of the Planck measurement of the CIB anisotropy power spectrum. Find SF efficiency must peak on a halo mass scale of 5e12 Msun and the IR luminosity per unit mass must increase rapidly with redshift. Compare predictions with well-calibrated phenomenological model for shot noise, and with direct observation of source counts; show that the mean duty cycle of the underlying IR sources must be near unity, indicating that the CIB is dominated by long-lived quiescent SF, rather than intermittent short "star bursts". Despite the improved flexibility of the model, the best simultaneous fit to all four Planck channels remains relatively poor. Discuss possible further extensions to alleviate the remaining tension with the data. Model presents theoretical framework for a joint analysis of bout BG anisotropy and source count measurements.
1103.0303
Likelihood approach to the first DM results from XENON 100
XENON100 collaboration
Direct detection of DM: distinguish dominant BG from the expected weak signals, based on some measured discrimination parameter. Systematic detector uncertainties as well as astrophysical uncertainties included in the model. The statistical model can be used to either set and exclusion limit or to make a discovery claim; properly treats systematic and statistical uncertainties. Apply model to the first data release of XENON100; place stronger limits on the spin-independent elastic WIMP-nucleon scattering cross-section. Derive a single limit, including all relevant systematic uncertainties, with a minimum of 2.4e-44 cm^2 for WIMPs with a mass of 50 GeV/c^2.
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