Day 694

Tuesday.

1407.0393
Measuring anisotropies in the Cosmic Neutrino Background
Lisanti, Safdi, Tully

Should observe a nearly isotropic background, a small dipole anisotropy in the CvB is expected due to the peculiar and spin distributions by polarizing the tritium targets.

1407.0394
The universal nature of sub halo accretion
Libeskind, Knebe, Hoffman, Gottloeber

Angular infall pattern of sub haloes onto host haloes in the context of LSS.  Find this infall pattern is essentially driven by the shear tensor of the ambient velocity field.  DM sub haloes found to be preferentially accreted along the principal aegis of the shear tensor which corresponds to the direction of weakest collapse.  Examine the dependence of this preferential infall on sub halo mass, host halo mass and redshift.  Although strongest for the most massive hosts and the most massive sub haloes at high z, the preferential infall of sub haloes is effectively universal in the sense that its always aligned with the axis of weakest collapse of the velocity shear tensor, the same shear tensor that dictates the structure of the cosmic web and hence the shear field emerges as the key factor that governs the local isotropic pattern of structure formation.  Since the small (sub-Mpc) scale is strongly correlated with the mid-range (~10 Mpc) scale -- a scale accessible by current surveys of peculiar velocities -- it follows that findings presented here open a new window into the relation between the observed LSS unveiled by current surveys of peculiar velocities and the preferential infall direction of the LG.  

1407.1315
Insights on the stellar mass-metallicity relation from the CALIFA survey
Delgado, et al

300 galaxies, spatially and temporally resolved maps, from CALIFA: investigate how Z* relates to the M* and the local mass surface density (mu*) in both spheroidal and disk dominated galaxies.  The galaxies are shown to follow a clear stellar mass-metallicity relation (MZR) over the whole 1e8 to 1e12 Msun range.  This relation is steeper than the one derived from nebular abundances, which is similar to the flatter stellar MZR derived when only young stars are considered.  Also find a strong relation between the local values of mu* and Z* (the muZR), betraying the influence of local factors in determining Z*.  This shows that both local (mu*-driven) and global (M*-driven) processes are important in determining the metallicity in galaxies.  Find that the overall balance between local and global effects varies with the location within a galaxy.  In disks, mu* regulates Z*, producing a strong muZR whose amplitude is modulated by M*.  In spheroids it is M* who dominates the physics of SF and chemical enrichment, with mu* playing a minor, secondary role.  Thses findings agree with the previous analysis of the SFHs of CALIFA galaxies, which showed that mean stellar yes are mainly governed by surface density in galaxy disks and by total mass in spheroids.

1407.1316
AGN-driven helium reionization and the incidence of extended HeIII regions at redshift z>3
Compostella, Cantalupo, Porciani

Use hydrosims post-processesed with radiative transfer code RADAMESH to assess recent claims that the low HeII opacity observed in z>3 quasar spectra may be incompatible with models of HeII deionization driven by the observed population of AGNs.  In particular, building upon the previous work, consider an early population of sources and stars the radiative transfer calculation at z>=5.  Model faithfully reproduces the emissivity of optically selected AGNs as inferred from measurements of their luminosity function.  Find that HeII deionization is very extended in z (Delta z>=2) and high spatially inhomogeneous.  In fact, mock spectra extracted from the simulations show a large variability in the evolution of the HeII effective optical depth within chunks of size Delta z = 0.04.  Regions with low opacity can be found at high z, in agreement with most recent observations of UV-transmitting quasars.  At the highest z currently probed by observations (z~3.4), the updated model predicts a much lower HeII effective optical depth than previous simulations in the literature relieving most of the tension with the current data, that, however, still persists at about the Gaussian 2 sigma level.  Given the very small number of observed lines of sight, the analysis indicates the current data cannot rule out a purely AGN-driven scenario with high statistical significance.

1407.1374
The mass spectrum of the first stars
Susa, Hasegawa, Tominaga

Perform cosmo hydro sims with non-equilibrium primordial chemistry to obtain 59 mini halos that host first stars.  The obtained mini halos are used as ICs of local 3 dimensional radiation hydrodynamics simulations to investigate the formation of the first stars.  Find 2/3 of the mini halos host multiple stars, while the rest of them have single stars.  The mass of the stars found in the simulations are in the range of 1 Msun<M<300 Msun, peaking at several 10 Msun.  Most of the very massive stars of <140Msun are born as single stars, although not all of the single stars are very massive.  Also find a few stars of 1 Msun that are kicked by the gravitational 3 body interactions to the position distant from the center of mass.  The frequency that a SF mini halo contains a binary system is ~50%.  Also investigate the abundance pattern of the stellar remnants by summing up the contributions from the first stars in the simulations.  Consequently, the pattern is compatible with that of the low metallicity Damped Lyman-alpha systems of the extremely metal poor stars, if the mass spectrum obtained in our experiment is shifted to the low mass side by 0.2 dex.  The case where an EMP star is born in the remnant of the individual mini halo without mixing with others, the chemical signature of the pair instability supernova is more prominent, because most of them are born as single stars.