Day 332

Thursday.

1211.3114
A successful broad-band survey for giant Lya Nebulae II: spectroscopic confirmation
Prescott, Dey, Jannuzi

Broad-band search technique for Lya "blob" at 2<z<3.  26 candidates, 5 confirmed spectroscopically to have Lya emission at 1.7<z<2.7, 4 of which are new.  Most show spatially-extended continuum emission.  Other candidates show no strong emission lines, but exhibit featureless, diffuse, blue continuum spectra.  Some may be lying in the redshift desert 1.2<z<1.6.  

1211.3117
On the road to more realistic galaxy cluster simulations: the effects of radiative cooling and thermal feedback prescriptions on the observational properties of simulated galaxy clusters
Skory, et al

Flux limited x-ray surveys of galaxy clusters show that clusters come in two roughly equally proportioned varieties: "cool core" clusters and non-"cool core" clusters (CCs and NCCs).  Shown: NCCs are often consistent with early major merger events that destroy embryonic CCs.  Conduct series of simulations using different methods of gas cooling, and of energy and metal feedback from SNe; attempt to produce a population of clusters with realistic central cooling times, entropies, and temperatures.  Find that the use of metallicity-dependent gas cooling is essential to prevent early overcooling, and that adjusting the amount of energy and metal feedback can have a significant impact on observable X-ray quantities of the gas.  Able to produce clusters with more realistic central observable quantities than before.  But still significant discrepancies between the simulated clusters and observations.  A subgrid method of modeling galaxy feedback in clusters may ameliorate the discrepancies between simulations and observations.

1211.3118
Galactic fly-bys: new source of Lithium production
Prodanovic, Bogdanovic, Urosevic

Low-Z halo stars have 7Li abundance 3x lower than predicted primordial abundance: (i) lack of understanding of Li destruction mechanism in stars, or (ii) non-standard physics behind the BBN?  (Li observation is difficult in stars.)  Proposed: uncertainties related to destruction of Li in stars can be circumvented by observing Li in gas phase of low metallicity systems, such as SMC, where the Li abundance values are expected to be primordial.  Propose: Another mechanism responsible for Li production in systems like the SMC where cosmic rays can be accelerated in tidal interactions caused by galactic fly-bys.  Show: large-scale tidal shocks from a few fly-bys could produce lithium in the amounts comparable to those expected from interactions of the galactic cosmic-rays (GCR) produced in SNe over the entire history of a system.  But the measured Li abundance is already consistent with predicted primordial abundance, so there is little room for contributions from other sources.  Adding a new mechanism for production of lithium, such as the tidal cosmic rays, would cause even more tension with the standard BBN theory, and be more in favor of the non-standard physics as a possible solution to the pressing Li problem.

1211.3119
A model for (non-lognormal) density distributions in isothermal turbulence
Hopkins

Physically motivated fitting function for density PDFs in turbulent gas.  Known: when gas is isothermal, the PDF is approximately lognormal in the core; high-resolution simulations show large deviations from exact log-normality.  The proposed function provides an extraordinarily accurate deescription of the density PDFs in simulations with Mach numbers ~0.1-15 and dispersion in log(rho) from ~0.01-4 dex.  Compared to a lognormal or lognormal-skew-kurtosis model, the fits are improved by orders of magnitude in the wings of the distribution (with fewer free parameters).  Deviation from log normality represented by parameter T that increases with the compressive Mach number.  ... Mass conservation requires violations of log-normal statistics.