1212.2223
Lessons from cosmic history: the case for a linear star formation -- H2 relation
Feldmann
SF in galaxies closely correlated with abundance of H2. Modeling is however challenging from first principles, and many question regarding its properties remain open. Exact functional form or the relation, whether it applies to high z (z>4), where CO observations are sparse. Analyze how the shape of the SF-gas relation affects the cosmic SFH and global galaxy properties using an analytic model that follows the average evolution of galaxies in DM haloes across cosmic time. Show that a linear relation with an H2 depletion time of 2.5 Gyr, as found in studies of nearby galaxies, results in good agreement with current observations of galaxies both low and high redshift. These observations include the evolution of the cosmic SFR density, the 4<z<9 UV LF, the evolution of the mass-metallicity relation, the relation between stellar and halo mass, and the gas-to-stellar mass ratios of galaxies. In contrast, the short depletion times that result from adopting a highly super-linear SF - gas relation lead to large SFR, substantial metal enrihment (0.1 solar), and low gas-to-stellar mass ratios already at z~10, in disagreement with observations. These results can be understood in terms of an equilibrium picture of galaxy evolution in which gas inflows, outflows, and SF drive the metallicities and gas fractions toward equilibrium values that are determined by the ratio of the gas accretion time to the gas depletion time. IN this picture, the cosmic modulation of the accretion rate is the primary process that drives the evolution of stellar masses, gas masses, and metallicities of galaxies from high z until today.
1212.2239
Characterization of ICM temperature distributions of 62 galaxy clusters with XMM-Newton
Frank, et al
Measure ICM temperature distribution in HIFLUGCS (X-ray limited sample). Search for correlations between the width of the temperature distributions and other cluster properties, including median cluster temperature, luminosity, size, presence of a cool core, AGN activity, and dynamical state. Use a MCMC analysis which models the ICM as a collection of X-ray emitting smoothed particles of plasma. Each smoothed particle is given its own set of parameters, including temperature, spatial position, redshift, size and emission measure. Allows measurement of temperature distribution median temperature, total emission measure. Find that none of the clusters have a temperature width, sigma_kT, consistent with isothermally. Counterintuitively, also find that the temperature distribution widths of disturbed, non-cool-core, and AGN-free clusters tend to be wider than in other clusters [why counterintuitive? Shouldn't it be that way?]. A linear fit to sigma_kT-kT_med finds sigma ~ 0.20 kT_med + 1.08, with an estimated intrinsic scatter of ~0.55 keV, demonstrating a large range in ICM thermal histories.
1212.2288
Te ATLAS3D project - XXII. Low-efficiency star formation in early-type galaxies: hydrodnamic models and observations
Martig, ... Alatolo, Blitz, ... Dekel, ... et al
Early-type galaxies are offset from the spirals on the large-scale Kennicutt relation, and form stars 2-5x less efficiently; in agreement with results on morphological quenching: gas disks are more stable against SF when embedded in early-type galaxies due to the lower disc self-gravity and increased shear. These gas discs do not fragment into dense clumps and do not reach as high densities as in the spiral galaxies. Explains the overall lower SF efficiency. Analyze a sample of local early-type and spiral galaxies, measuring their CO and HI surface densities and their SFR as determined by their non-stellar 8um emission. As predicted by the simulations, we find that the early-type galaxies are offset from the Kennicutt relation compared to the spirals, with a twice lower efficiency. Finally, validate approach by performing a direct comparison between models and observations. Run a simulation designed to mimic the stellar and gaseous properties of NGC524, a lenticular galaxy, and find a gas disc structure and global SFR in good agreement with the observations. "Morphological quenching" thus seems to be a robust mechanism, and is also consistent with other observations of a reduced SFE in early-type galaxies in the COLD GASS survey. This lower efficiency of SF is not enough to explain the formation of the whole Red Sequence, but can contribute to the reddening of some galaxies.
1212.2295
Recurrent novae as progenitors of Type Ia supernovae
Kato, Hachisu
Recurrent novae are considered as cancidates of progenitors of Type Ia SNe. A natural SD scenario candidate.
1212.2624
Dynamical analysis of strong-lensing galaxy groups at intermediate redshift
Munoz et al
7 galaxy groups at 0.3<z<0.7. The groups were selected from the SL2S (Strong Lensing legacy Survey), a systematic SL search in CFHTLS. Velocity dispersions between 300 and 800 km/s, with 1e13-14 Msun mass. Isolated groups, but two showing evidence of an ongoing merger of two sub-structures. Find a good agreement between the velocity dispersions estimated from the analysis of the kinematics of group galaxies and the WL measurements, and conclude that the dynamics of baryonic matter is a good tracer of the total mass content in galaxy groups.
1212.2371
The effect of probe dynamics on galactic exploration timescales
Forgan, Papadogiannakis, Kitching
* Fermi's paradox: the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilization and humanity's lack of contact with, or evidence for, such civilizations. "Where is everybody?"
Previous assumptions assumed constant maximum velocity, but slingshot maneouvers can provide significant velocity boosts at little to no fuel cost. Investigate the effects of these techniques; present multiple realization of single probes exploring a small patch of the MW. Find that adding slingshot velocity boosts can decrease the travel type by up to 100x of magnitude over simple powered flight.
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