Day 593

Thursday.

1402.4480
The effect of gravitational tides on dwarf spheroidal galaxies
Nichols, Revaz, Jablonka

From simulation, study from both dynamical and chemical point of view.  Find: tidal effects quench the SF even inside gas-endowed dwarfs.  Such quenching may produce the radial distribution of dwarf spheroidals from the orbits seen within large cosmological simulations.  Also find that the metallicity gradient within a dwarf is gradually erased through tidal interactions as stellar orbits move to higher radii.  The model dwarfs also shift to higher <[Fe/H]>/L ratios, but only when losing >20% of stellar mass.

1402.4482
AGN-driven outflows without quenching in simulations of high-redshift disk galaxies
Gabor, Bournaud

Study AGNs using high-res sims of idealized z=2 isolated disk galaxies.  Episodic accretion events lead to outflows with velocities >1000 km/s and mass outflow rates up to the SFR (several tens of Msun/yr).  Outflowing winds escape perpendicular to the disk with wide opening angles, and are typically asymmetric (i.e., unipolar) because dense gas above or below the AGN in the resolved disk inhibits outflow.  Owing to rapid variability in the accretion rates, outflowing gas may be detectable even when the AGN is effectively "off".  The highest velocity outflows are concentrated within 2-3 kpc of the galactic center during the peak accretion.  With the purely thermal AGN feedback model -- standard in previous literature -- the outflowing material is mostly hot (1e6K) and diffuse (nH<1e-2 cm^-3), but includes a cold component entrained in the hot wind.  Despite the powerful bursts and outflow rates near the SFR, AGN feedback has little effect on the dense gas in the galaxy disk.

1402.4484
The X-ray properties of weak lensing selected galaxy clusters
Giles, … Hamana, Miyazaki, … Ellis, Massey

X-ray follow-up targeting 10 WL-selected clusters from Subaru WL survey.  8 clusters studied with Chandra, remaining 2 from archival X-ray data.  The WL clusters appear to fit the same scaling relation between X-ray luminosity and temperature as X-ray selected clusters.  However, when L-M relation considered, the WL selected clusters appear under luminous by a factor 3.8pm0.9 (or more massive by 2.9pm0.2), compared to X-ray selected clusters.  Only by considering various observational effects that could potentially bias WL mass, can this difference be reconciled.  Used X-ray imaging data to quantify the dynamical state of the clusters and found that one of the clusters appears dynamically relaxed, and two of the clusters host a cool core, consistent with SZ-selected clusters.  Results suggest that regular, cool core clusters may be over-represented in X-ray selected samples.  [what was the WL cluster selection criteria?  WL mass?  Then more "massive" clusters may be preferred with WL selection.]

1402.4766
Giant sparks at cosmological distances?
Kulkarni, et al

Millisecond duration bright radio pulses in the 1.4 GHz band and with inferred dispersion measures (DM) well in excess of galactic values have been reported by Lorimer et al. and Thornton et al.  The all-sky rate of these events is large, ~1e4 per day above ~1 Jy.  To add to the mystery, there now exists "Perytons" -- also pulsed and dispersed sources but most certainly of local (artificial or atmospheric) origin.  The suggested models now range from sources originating in the Earth's atmosphere, in stellar coronae, in other galaxies and at even cosmological distances.  Using a series of physically motivated assumptions combined with the observed properties of these bursts, explore possible constraints on sites or processes that can account for such high DMs.  In the analysis, focus on the first such reported event by Lorimer+: a 30 Jy, 5-ms duration burst with a dispersion measure of 375 cm^-3 pc and exhibiting a steep frequency-dependent pulse width ("the Sparker").  Assuming that the DM of the Sparker is produced by propagation through a cold plasma and using all available observations, constrain its distance to be greater than 300 kpc.  A similar analysis on the 4 other reported events (all with larger DMs) would lead to a stronger conclusion, namely these Fast Radio Bursts (FRBs) are of extragalactic origin, provided that the inferred DM arises due to propagation through cold plasma.  Explore proposed extra-galactic as well as stellar coronal models for FRBs and find most of them either unable to account for the high daily rate or have difficulty in having an ultra-clean explosion site (essential to the production of high brightness temperature pulse) or suffer from free-free absorption on length scales beyond the immediate production of the radio pulses.