Day 688

Monday.

1406.7003
The most metal-poor damped Lyman alpha systems: an insight into dwarf galaxies at high redshift
Cooke, Pettini, Jorgenson

Analyze the kinematics, chemistry, and physical properties of a sample of the most metal-poor damped Lyman alpha systems (DLAs), to uncover their links to modern-day galaxies.  Present evidence that the DLA population as a whole exhibits a 'knee' in the relative abundances of the alpha-capture and Fe-peakelements when the metallicity is [Fe/H]~-2.0.  In this respect, the chemical evolution of DLAs is clearly different form that experienced by MW halo stars, but resembles that of dwarf spheroidal galaxies in the Local Group.  Also find a close correspondence between the kinematics of LG dwarf galaxies and of high z metal-poor DLAs, which further strengthens this connection.  On the basis of such similarities, propose that the most metal-poor DLAs provide the unique opportunity to directly study the dwarf galaxy population more than 10B years in the past, at a time when many dwarf galaxies were forming the bulk of their stars.  To this end, measure some f the key physical properties of the DLA gas, including their neutral gas mass, size, kinetic temperature, density, and turbulence.  Find that metal-poor DLAs mostly consist of a warm neutral medium with T_gas~9600K predominantly held up by thermal pressure.  All of the DLAs in the sample exhibit a subsonic turbulent Mach number, implying that the gas distribution is largely smooth.  These results are among the first empirical descriptions of the environments where the first few generation of stars may have formed in the universe.

1406.7284
Exploring the diffuse interstellar bands with the Sloan Digital Sky Survey
Lan, Ménard, Zhu

Use star, galaxy, and quasar spectra in SDSS to map out the distribution of diffuse interstellar bands (DIBs) induced by the MW.  Show that, after carefully removing the intrinsic SED of each source, it is possible to measure statistical flux fluctuations at the 1e-3 level, detect about thirty DIBs and measure their strength as a function of position on the sky.  Create a map of DIB absorption covering about 5000 sq deg and measure correlations with various tracers of the ISM: atomic & molecular H, dust and PAHs.  After recovering known correlations, show that each DIB has a different dependence on atomic and molecular H: while they are all positively correlated with N(HI), they exhibit a range of behaviors with N(H2) showing positive, negative or no correlation.  Show that a simple parameterization involving only N(HI) and N(H2) applied to all the DIBs is sufficient to reproduce a large collection of observational results reported in the literature: it allows a natural description of the relations between DIB strength and dust reddening (including the so-called skin effect), the related scatter, DIB pair-wise correlations & families, the affinity for a sigma/zeta-type environments and other correlations related to molecules.  This approach allows characterization of DIB dependencies in a simple manner and provides a metric to characterize the similarities between different DIBs.