Day 304

Monday.

1209.4636
The unbiased measurement of UV spectral slopes in low luminosity galaxies at z=7
Rogers, McLure, Dunlop

UV continuum slope beta at z=7 in HST WFC3/IR bans via the J-H color, is a useful indicator of the age, metallicity, and dust content of high-z stellar populations.  Redward evolution of beta with cosmic time from z=7 to 4 can be explained by a build up of dust.  Use source recovery simulations to address how to best measure the UV slope of z=7 galaxies.  Source detection, selection and color measurement each biased the previous measurements of beta; find robust method for measuring beta in the simulations, then remeasure the UV slopes.  Sample appears consistent with an intrinsic distribution of normal star-forming galaxies with beta=-2, but need further imaging from HUDF12.  Additional F140W filter would help.

1209.4639
Radio mini-halo emission from cosmic rays in galaxy clusters and heating of the cool cores
Fujita, Ohira

Proposed: cool cores of galaxy clusters are stably heated by cosmic rays (CRs); then radio mini haloes (often found in the central regions of cool core clusters) may be attributed to the synchrotron emission from the CRs.  Investigate radial profiles of mini-haloes; confirm that radiative cooling of ICM is balanced with the heating by CR streaming.  Streaming velocity of CRs is the sound velocity of the ICM; heating is even more stable that the case where the streaming velocity is the Alfven velocity.  Assume cooling / heating equilibrium, estimate radial profiles of CR pressure in 6 clusters from x-ray observations only.  Compare prediction to observed.  Since CR protons interact with ICM protons, can predict the radial profiles of the resultant synchrotron radiation.  Compare the predictions with the observed radial profiles of the mini-haloes in the six clusters and find that they are consistent if the momentum spectra of the CRs are steep.  These results may indicate that the cores are actually being heated by the CRs.  Also predict broad-band spectra of the 6 clusters, and show that non-thermal fluxes from the clusters are small in hard x-ray and gamma-ray bands.

1209.4643
Subary weak-lensing measurement of a z=0.81 cluster discovered by the Atacama cosmology telescope survey
Miyatake, .. Takada, et al

High-z SZ cluster from ACT, measured in WL.  Use GL model-fitting method (PSF effects removed).  Astrometric distortion effects accounted for.  BG gal selection: use photo-z from BrizY (PSF matching/homogenization).  S/N ~ 3.7.  Fit NFW model to shear profile, find M200 (rho-bar_m) = 7.5e14 Msun/h.  Consistent with SZ mass estimates, assuming hydrostatic equilibrium and virial theorem; scaling relation between SZ signal and mass derived from WL, X-ray and velocity dispersion, within measurement errors.  Existence of this cluster consistent with cluster abundance prediction of LCDM model.

1209.4661
The extragalactic background light and the gamma-ray opacity of the universe
Dwek, Krennrich

Extragalactic background light (EBL) plays a crucial role in cosmological tests (resolved, unresolved, and truly diffuse background) for the formation and evolution of stellar objects and galaxies, and for setting limits on exotic energy releases in the universe.  EBL also plays an important role in the propagation of very high energy gamma-rays which are attenuated en rout to z=0 by pair producing gamma-gamma interactions with the EBL and CMB.  EBL affects the spectrum of the sources (predominantly blazars) in the 10GeV to 10 TeV range.  Knowledge of the EBL intensity and spectrum will sllow the determination of the intrinsic blazar spectrum in a crucial energy regime that can be used to test particle acceleration mechanisms and VHE gamma-ray production models.  Conversely, knowledge of the intrinsic gamma-ray spectrum and the detection of blazars at increasingly higher z will set strong limits on the EBL and its evolution.  Review of EBL determination and its impact on the current understanding of the origin and production mechanisms of gamma-rays in blazers, and on energy releases in the universe.  Summary and future directions in Cherenkov Telescope Array techniques.

1209.4676
A massive bubble of extremely metal poor gas around a collapsing Ly-alpha blob at z=2.54
Humphrey et al

Gaseous environment of the radio-loud quasar at z=2.54, associated with a large Ly-alpha nebula, and a spatially extended Ly-alpha-absorbing structure.  Measure kinematic properties consistent with infall rate of 10/100 M./yr for the nebula, at radius >40 kpc from the quasar.  Absorption in NV, CIV, SiIV with no unambiguous detection of absorption lines from any low-ionization species of metal.  Absorbing gas predominantly ionized by the quasar.  Scenario involving SB-driven super-bubbles, and creation of infalling filaments?

1209.4688
The first stars
Whalen

[invited review talk]  PopIII stars unlikely to be detected in the very near future; properties remain unknown.  Detect by (1) their SNe (2) reconciling their nucleosynthetic yields to the chemical abundances measured in ancient metal-poor stars in the galactic halo.  Problem in simulation of PopIII stars, discuss the best prospects for constraining their properties observationally in the near term.

1209.4762
The effect of peculiar velocities on the epoch of reionization (EoR) 21-cm signal
Majumdar, Bharadwaj, Choudhury

Semi-numerical simulations of reionization to study the behaviour of power spectrum of EoR 21-cm signal in both real and z-space.  Consider 2 models of reionization (homogeneous recombination (HR) and the other incorporating inhomogeneous recombination (IR)).  Predictions of both are similar in large scales.  Qualitative interpret the behaviour of both the real space and z space power spectra at large scales in terms of x_HI and the ratio P_xx/P_delta,delta.

1209.4783
Near-pristine gas at high redshifts: a window on early nucleosynthesis
Pettini, Cooke

A recently complete survey of the most metal-poor DLAs.  Clarified a number of lingering issues concerning the abundances of C, N, O in the low metallicity regime, revealed the existence of DLA analogues to Carbon-enhanced metal-poor stars, and provides some of the most precise measures of the primordial abundance of Deuterium.