Thursday.
1210.0530
Best practices for scientific computing
Aruliah et al
As the title says. Worth mentioning in JC.
1210.0899
Observational limits on the gas mass of a z=4.9 galaxy
Livermore, ... Bower, ... Richard, et al
A 22x magnified galaxy, CO(5-4) emission targeted. Gas mass at 1e9Msun, gas fraction (gas/(gas+star)) = 0.6. Difficult to observe molecular gas in this epoch. Without lensing, it will be tough to get gas mass.
1210.0903
A general theory of turbulent fragmentation
Hopkins
An analytic framework to understand fragmentation in turbulent, self-gravitating media. Fully time-dependent gravo-turbulent fragmentation & collapse. Turbulent systems are always gravitationally unstable (probabilistically). Fragmentation mass spectra, size/mass relations, correlation functions, range of scales over which fragmentation occurs, and time-dependent rates of fragmentation are predictable; depends on bulk turbulent properties. Generalize to include rotation, complicated EoS, collapsing/expanding background, B-fields, intermittency, and non-normal statistics. Fragmentation is suppressed with 'stiffer' EoS or different driving mechanisms. Suppression appears at an 'effective sonic scale' where Mach(R,rho)~1. Gas becomes stable below this scale for polytropic gamma>4/3, but fragmentation still occurs on larger scales. The scale-free nature of turbulence and gravity generically drives mass spectra and correlation functions towards universal shapes, with weak dependence on many properties of the media. Correlated fluctuation structures, non-Gaussian density distributions, and intermittency have surprisingly small effects on the fragmentation process. This is because fragmentation cascades on small scales are 'frozen in' when large-scale modes push the 'parent' region above the collapse threshold; though they collapse, their statistics are only weakly modified by the collapse process. With thermal support, structure develops 'top-down' in time via fragmentation cascades; but strong rotational support reverses this to 'bottom-up' growth via mergers & introduces a maximal instability scale distinct from the Toomre scale.
1210.0932
Lunar accretion from a Roche-interior fluid disk
Salmon, Canup
Hybrid numerical approach to simulate the formation of the Moon from an impact-generated disk. Fluid model for the disk inside the Roche limit, and an N-body code to describe accretion outside the Roche limit. The inner disk spreads due to a thermally regulated viscosity, material is delivered across the Roche limit and accretes into moonlets that are added to the N-body sim. The final state of the Moon's growth is controlled by the slow spreading of the inner disk, resulting in a total lunar accretion timescale of ~100 years (not a few months, as in N-body only sims). Proposed: inner disk may compositionally equilibriate with the Earth through diffusive mixing, which offers a potential explanation for the identical oxygen isotope compositions of the Earth and Moon; but the mass fraction of the final Moon derived from the inner disk is limited by resonant torques bewteen the disk and exterior growing moons. Initial disks containing <2.5 lunar masses find final moon with mass >0.8 M_L contains <60% material derived from the inner disk, with this material preferentially delivered to the Moon at the end of its accretion.
1210.1025
The evolution of active galactic nuclei and their spins
Volonteri et al
Find: typical spin and radiative efficiency of MBHs decrease with cosmic time because of the higher incidence of stochastic processes in gas-rich galaxies and MBH-MBH mergers in gas-poor galaxies. At z=0 the spin distribution in gas-poor galaxies peaks at spins 0.4-0.8, and is not mass dependent. MBHs in gas-rich galaxies have a more complex evolution, with low-mass MBHs at low redshift having low spins, and spins increasing at larger masses and redshifts. Find: z>1 MBH spins are on average highest in high luminosity AGN, while at lower redshifts these differences disappear.
1210.1035
The evolving interstellar medium of star forming galaxies since z=2 as probed by their infrared spectral energy distributions
Magdis, et al
Derive Mdust from MIR to millimeter wavelength stacked ensembles at 0.5<z<2 in MS galaxies, which obey a tight correlation between SFR and M*. For star bursting galaxies that falls outside that relation. Exploit correlation of gas to dust mass with metallicity, and use these measurements to constrain the gas conent, CO-to-H2 conversion factors, and SFE of these galaxies. SFE lower at higher z, while a_co higher, compared to local MS galaxies with equivalent high IR luminosities. Variation of sSFR=SFR/M* are driven by varying gas fractions. For massive galaxies, show that the hardness of the radiation field <U> and the primary parameter defining the shape of the SED is equivalent to SFE/Z. For MS galaxies, measure <U>, showing that it does not depend significantly on either the stellar mass or the sSFR. Show that <U> = LIR/Mdust does evolve, with MS galaxies having harder radiation fields, and thus warmer temperatures as redshift increases from z=0 to 2; can be understood based on z evolution of M*-Z and SFR-M* relations. Motivate the construction of a universal set of SED templates for MS galaxies which vary as a function of z with only one parameter, <U>.
1210.1093
The origin of the chemical elements in cluster cores
de Plaa
ICM has metal lines from C to Zn within 0.1-10keV. Abundance of 11 elements studied; most elements formed in SNIa or II (core collapse) which have very different chemical yields. Massive stars and AGB stars contribute by providing most of the C and N in the ICM. Feedback processes suppress SF in cluster core; element abundances directly probe the SFH of the majority of stars formed between z=2 and 3. Spatial distribution in the core and evolution with z provide information about how these elements are transported from the member galaxies to the ICM.
1210.1114
Heliophysics gleaned from seismology
Gough
Heliophysical inferences drawn from seismology briefly described. Use of simple formulae, to answer specific questions about physics.
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