Day 788

Tuesday.

1411.4052
On the signature of the baryon-dark matter relative velocity in the two and three-point galaxy correlation functions
Slepian, Eisenstein

Develop a configuration-space picture of the relative velocity between baryons and DM that clearly explains how it can shift the BAO scale in the galaxy-galaxy correlation function.  The shift occurs because the relative velocity is non-zero only within the sound horizon and thus adds to the correlation function asymmetrically about the BAO peak.  Further show that in configuration space the relative velocity has a localized, distinctive signature in the 3PCF.  In particular, find that a multipole decomposition is a favorable way to isolate the relative velocity in the 3PCF, and that there is a strong signature in the ell=1 multipole for triangles with 2 sides around the BAO scale.  Investigate a further compression of the 3PCF to a function of only one triangle side that preserves the localized nature of the relative velocity signature while also nicely separating linear from non-linear bias.  Expect that this scheme will substantially lessen the computational burden of finding the relative velocity in the 3PCF.  The relative velocity's 3PCF signature can be used to correct the shift induced in the galaxy-galaxy correlation function so that no systematic error due to this effect is introduced into the BAO as used for precision cosmology.

1411.4189
The chemical signature of surviving population III stars in the Milky Way
Johnson

Simulations suggest IMF of Pop III stars may have extended to sub-solar masses.  If <0.8Msun PopIII stars did form, then they should still be present n the Galaxy today as either MS or red giant stars.  None found to date; but possibly because the metal-free nature of primordial stars are masked due to accretion of metal-enriched material from the ISM over the course of their long lifetimes.  Point out that while gas accretion from the ISM may readily occur, the accretion of dust from ISM can be prevented due to radiation pressure from the low-mass stars.  This implies a possible unique chemical signature for stars polluted only via accretion: an enhancement in gas phase elements relative to those in the dust phase.  Outline the conditions in which this signature could be exhibited, and derive the expected signature for the case of accretion from the local ISM.  Due to the large fraction of Fe depleted into dust relative to that of C and other elements, this signature is similar to that observed in many of the so-called carbon-enhanced metal-poor (CEMP) stars.  Therefore suggest that some fraction of the observed CEMP stars may, in fact, be accretion-polluted Pop III stars.  Find that this effect could also be at play in accretion flows onto protostars, implying that it may also impact the chemical signatures of Pop II stars.

1411.4574
Dust destruction rates and lifetimes in the Magellanic clouds
Temim, et al

The nature, composition, abundance, and size distribution of dust in galaxies is determined by the rate at which it is created in the different stellar sources and destroyed by interstellar shocks.  Because of their extensive wavelength coverage, proximity, and nearly face-on geometry, the MCs provide a unique opportunity to study these processes in great detail.  IN this paper, use the complete sample of SN remnants (SNRs) in the MCs to calculate the lifetime and destruction efficiencies of silicate and carbon dust in these galaxies.  Find dust lifetimes of 22pm13 Myr (30pm17Myr) for silicate (carbon) grains in the LMC, and 54pm32 Myr (72pm43 Myr) for silicate (carbon) grains in the SMC.  The significantly shorter lifetimes in the MCs, as compared to the MW, are explained as the combined effect of their lower total dust mass, and the fact that the dust-destroying isolated SNe in the MCs seem to preferentially occurring in regions with higher than average dust-to-gas (D2G) mass ratios.  Also calculate the SNe rate and the current SFR in the MCs, and use them to derive maximum dust injection rates by asymptotic giant branch stars and core collapse SNe.  Find that the injection rates are an order of magnitude lower than the dust destruction rates by the SNRs.  This supports the conclusion that, unless the dust destruction rates have been considerably overestimated, most of the dust must be reconstituted from surviving grains in dense molecular clouds.  More generally, also discuss the dependence of the dust destruction rate on the local D2G mass ratio, the ambient gas density and metallicity, as well as the application of the results to other galaxies and dust evolution models.