Day 406

Monday.

1304.1270
The CMB asymmetry from inflation
Lyth

Erickcek, Kamionkowski and Carroll have proposed that the hemispherical asymmetry of the CMB could be due to a very large scale perturbation of the field phi causing the primordial curvature.  Show that the asymmetry is too small to agree with observation if phi is the inflaton of single-field inflations.  If instead phi is a curvaton-type field, the asymmetry is proportional to \fnl(k), and can have the required magnitude and scale-dependence.

1304.1279
Large-scale radio continuum properties of 19 Virgo cluster galaxies The influence of tidal interactions, ram pressure stripping, and accreting gas envelopes
Vollmer et al

VLA 20 and 6cm observations of 19 Virgo spirals, contains 6 galaxies with "a global minimum of 20 cm polarized emission at the receding side of the galactic disk" [?] and quadrupolar type large-scale B-fields.  No additional case of ram-pressure stripped spiral galaxy with an asymmetric ridge of polarized radio continuum emission was found.  In the absence of close companion, a truncated HI disk, together with a ridge of polarized radio continuum emission at the outer edge of the HI disk, is a signpost of ram pressure stripping.  6 out of 19 observed galaxies display asymmetric 6 cm polarized emission distributions.  3 galaxies belong to tidally interacting pairs, 2 host huge accreting HI envelopes, and 1 had a recent minor merger. Tidal interactions and accreting gas envelopes can lead to compression and shear motions which enhance the polarized radio continuum emission.  Galaxies with low average SFR per unit area have a low average degree of polarization.  Shear or compression motions can enhance the degree of polarization.  The average degree of polarization of tidally interacting galaxies is generally lower than expected for a given rotation velocity and SF activity.  This low average degree of polarization is at least partly due to the absence of polarized emission from the thin disk.  Ram pressure stripping can decrease whereas tidal interactions most frequently decreases the average degree of polarization of Virgo spiral galaxies.  Found: moderate active ram pressure stripping has no influence on the spectral index, but enhances the global radio continuum emission with respect to the FIR emission, while an accreting gas envelope can but not necessarily enhance the radio continuum emission with respect to the FIR emission.

1304.1539
Taking the "Un" out of "Unnovae"
Piro

Long expected that some massive stars produce stellar mass BHs upon death, but observational signature of such events has been unclear.  Suggested that the result may be an "unnova," in which the formation of a BH is marked by the disappearance of a star rather than an EM outburst.  Argue that when the progenitor is a red supergiant, evidence for BH creation may instead be a ~3-10 day optical transient with a peak luminosity of ~1e40-41 erg/s, a temperature of 1e4K, slow ejection speeds of ~200 km/s, and a spectrum devoid of the nucleosynthetic products associated with explosive burning.  This signal is the breakout of a shock generated by the hydrodynamic response of a massive stellar envelope when the protoneutron star loses ~few*0.1Msun to neutrino emission prior to collapse to a BH.  Current and future wide-field, high-cadence optical surveys make this an ideal time to discover and study these events.  Motivated by the unique parameter space probed by this scenario, discuss more broadly the range of properties expected for shock breakout flashes, with emphasis on progenitors with large radii and/or small shock energies.  This may have application in a wider diversity of explosive events, from pair instability SNe to newly discovered but yet to be understood transients.

1304.1633
Coevolution of dust, gas, and stars in galaxies - I. Spatial distributions and scaling-relations of dust and molecular hydrogen
Bekki

Investigate time evolution of dust properties, H2 contents, and SFH in galaxies by using chemodynamical simulations.  The sims include the formation of dust in the stellar winds of SNe and AGB stars, the growth and destruction processes of dust in the ISM, the formation of PAH dust in carbon-rich AGB stars, the H2 formation on dust grains, and the H2 photo-dissociation due to FUV light in a self-consistent manner.  Focus mainly on disk galaxies with different total masses in this preliminary study.  The principle results are as follows: the SFH of disk galaxies can be regulated by the time evolution of interstellar dust, mainly because the formation rates of H2 can be controlled by dust properties.  The observed correlation between dust-to-gas-ratios (D) and gas-phase O abundances (A_O=12+log(O/H)) can be reproduced reasonably well in the present models.  The disks show negative radial gradients (larger in inner regions) of H2 fraction (f_H2), PAH-to-dust mass ratio (f_PAH), D, and A_O and these gradients evolve with time.  The surface-mass densities of dust (Sigma_dust) are correlated more strongly with the total surface gas densities than with those of H2.  Local gaseous regions with higher D are more likely to have higher f_H2 in individual disks and total H2 masses correlate well with total dust masses.  More massive disk galaxies are more likely to have higher D, f_PAH, and f_H2 and smaller dust-to-stellar mass ratios.  Compare between galactic SFH in the metallicity-dependent and dust-dependent SF models and find no major differences.