Day 424

Wednesday.

1304.7769
The stellar initial mass function of ultra-faint dwarf galaxies: evidence for IMF variations with galactic environment
Geha, ... Kerby, et al

Present constraints on the stellar initial mass function (IMF) in two ultra-faint dwarf (UFD) galaxies, Hercules and Leo IV, based on deep HST/ACS imaging.  The two galaxies are extremely low luminosity (M_V=-6.2,-5.5), metal-poor (<[Fe/H]>=-2.4,-2.5) systems that have old stellar populations (>11 Gyr).  Because they have long relaxation times, can directly measure the low-mass stellar IMF by counting stars below the MS turnoff without correcting for dynamical evolution.  [Neat.]  IMF for stellar masses 0.52-0.77 Msun is best fit by power-law slope of alpha=1.2 pm 0.4 for Hercules and alpha=1.3pm0.8 for Leo IV.  Shallower than Salpeter IMF (alpha=2.35) and Kroupa IMF (alpha=2.3 for M>0.5Msun).  Simultaneously fit for the binary fraction, and find f_binary=0.47pm0.2ish for both.  The UFD binary fractions are consistent with that inferred for MW stars in the same mass range, despite very differenet metallicities.  In contrast, the IMF slopes in the UFDs are shallower than other galactic environments.  In the pass range 0.5-0.8 Msun, see a trend across the handful of galaxies with directly measured IMFs such that the power-law slopes becomes shallower (more bottom-light) with decreasing galactic velocity dispersion and metallicity.  This trend is qualitatively consistent with results in elliptical galaxies inferred via indirect methods and is direct evidence for IMF variations with galactic environment.

1304.7770
A Herschel [CII] galactic plane survey I: the global distribution of ISM gas components
Pineda, Langer, Velusamy, Goldsmith

[CII] 158um line is an important tool for understanding the life cycle of ISM.  Ionized carbon is present in a variety of phases of the ISM, including the diffuse ionized medium, warm and cold atomic clouds, clouds in transition from atomic to molecular, and dense and warm photon dominated regions (PDRs).  ... [CII] emission is mostly associated with spiral arms, mainly emerging from Galactocentric distances between 4 and 10 kpc.  Estimate that most of the observed [CII] emission is produced by dense PDRs (47%), with smaller contributions from CO-dark H2 gas (28%), cold atomic gas (21%), and ionized gas (4%).  Atomic gas inside Solar radius is mostly cold neutral medium (CNM), while the warm neutral medium gas dominates the outer galaxy.  The average fraction of CNM relative to total atomic gas is 43%.  Find that the warm and diffuse CO-dark H2 is distributed over a larger range of Galactocentric distances (4-11 kpc) than the cold and dense H2 gas traced by 12CO and 13CO (4-8 kpc).  The fraction of CO-dark H2 to total H2 increases with Galactocentric distance, ranging from 20% at 4 kpc to 80% at 10 kpc.  On average, CO-dark H2 accounts for 30% of the molecular mass of the MW.  When the CO-dark H2 component is included, the radial distribution of the CO-to-H2 conversion factor is steeper than that when only molecular gas traced by CO is considered.  Most of the observed [CII] emission emerging from dense PDRs is associated with modest FUV fields in the range chi0~1-30.

1304.7778
The massive end of the luminosity and stellar mass functions: Dependence on the fit to the light profile
Bernardi, Meert, Sheth, Vikram, ... Mei, etal

The massive end of the stellar MF is rather sensitive to how one fits the light profiles of the most luminous galaxies.  Can affect total stellar density at z~0.1 by 1.2x.  The differences are most pronounced at the massive end, where the measured number density of objects having M*>6e11 Msun 5x larger.  Impacts studies of the growth and assembly of stellar mass in galaxies, and of the relation between stellar and halo mass, so we provide simple analystic fits to these new L and stellar MF and quantify how they depend on morphology, as well as the binned counts in electronic format.

1304.7849
The Coyote universe extended: precision emulation of the matter power spectrum
Heitmann, Lawrence, Kwan, Habib, Higdon

Need prediction as accurate as the measurements, as well as robust estimates of systematic errors that are inherent to the modeling process.  In the NL regime of structure formation, this challenge can only be overcome by developing a large-scale, multi-physics simulation capability covering a range of cosmological models and astrophysical processes.  As a first step of achieving this goal, develop a prediction scheme for matter PS ("emulator"), accurate at the 1% level out to k~1/Mpc and z=1 for wCDM cosmologies based on a set of high-accuracy N-body simulations.  It is highly desirable to increase the range in both redshift and wavenumber and to extend the reach in cosmological parameter space.  To make progress in this direction while minimizing computational cost, present a strategy that maximally re-uses the original simulations.  Demonstrate improvement over the original spatial dynamic range by an order of magnitude, reaching k~10 h/Mpc, a 4-fold increase in z coverage, to z=4, and now include the Hubble parameter as a new independent variable.  To further the range in k and z, a new set of nested simulations run at modest cost is added to the original set.  The extension in h is performed by including perturbation theory results within a multi-scale procedure for building the emulator.  This economical methodology still gives excellent error control, ~5% near the edges of the domain of applicability of the emulator.  A public domain code for the new emulator is released as part of the work presented in in this paper.