Day 401

Tuesday.

1304.0006
Ultra-strong MgII absorbers as a signature of cool intragroup gas
Gauthier

Spectroscopic survey of galaxies in the vicinity of ultra-strong Mg II absorber at z=0.5624.  Projected separation of 246 kpc of an LRG at z=0.5604.  Two galaxies at rho<60 kpc and another at rho=209 kpc, all at z~0.562(3,1,3).  Indicate that the absorbing gas resides in a group environment.  Performr SPS analysis of the group members to characterize their SFH, on-going SFR, and stellar masses.  Find: two group members at rho<60 kpc are best characterized by old stellar populations (>1 Gyr) and little on-going SF activity (SFR<2.9 Msun/yr), while the thrid exhibit OII consistent with SFR>3.0 Msun/yr.  All three ultra-strong MgII absorbers (including previous studies) are found in groups.  Different physical mechanisms giving rise to the absorbing gas including: starburst driven-outflows, cold filaments, extended rotating disks, and stripped gas.  EW of these gas is more likely due to the gas dynamics of the intragroup medium rather than driven by starburst outflows.

1304.0010
The EGNoG survey: molecular gas in intermediate-redshift star-forming galaxies
Bauermeister, Blitz, ... et al

EGNoG (Evolution of molecular Gas in Normal Galaxies) survey is an observational study of molecular gas in 31 SF galaxies from z=0.05 to 0.5, with stellar masses of 4-30e10 Msun and SFR of 4-100 Msun/yr.  Observe CO(1-0) and CO(3-2) rotational lines using CARMA.  Detect 24 or 31 galaxies and present resolved maps for 10 galaxies in the lower redshift portion of the survey.  Use bimodal prescription for the CO to molecular gas conversion factor, based on specific SFR, and compare the EGNoG galaxies to a large sample of galaxies assembled from the literature.  Find an average molecular gas depletion time of 0.76 pm 0.54Gyr for normal galaxies, and 0.06 pm 0.04 Gyr for SB galaxies.  By expressing the molecular gas fraction in terms of the sSFR and molecular gas depletion time, also calculate the expected evolution of the molecular gas fraction with redshift.  The predicted behavior agrees well with the significant evolution observed from z~2.5 to today.

1304.0309
Robust strong lensing time delay estimation
Hojjati, Kim, Linder

Lightcurves of lensed images have measurement gaps, noise, systematics such as microlensing from substructure along an image line of sight, and no a priori functional model, making robust time delay estimation challenging.  Using Gaussian process techniques, demonstrate success in accurate blind reconstruction of time delays and reduction in uncertainties for real data.

1304.0324
The positron density in the intergalactic medium and the galactic 511 keV line
Vecchio, Vincent, Miralda-Excude, Pena-Garay

The 511 keV e-p annihilation line is highly concentrated towrads the Galactic centre.  Its origin remains unknown despite decades of scrutiny.  Propose a novel scenario in which known extragalactic positron sources such as radio jets of AGN fill the IGM with MeV e+e- pairs, which are then accreted into the MW.  Show that interpreting the diffuse CRB (CR background) as arising from radio sources with characteristics similar to the observed cores and radio lobes in powerful AGN jets suggests that the intergalactic positron-to-electron ratio could be as high as 1e-5, although this can be decrease if the CRB is not all produced by paris and if not all positrons escape to the IGM.  Assuming an accretion rate of one solar mass per year of matter into the MW, a e+/e- ratio of only 1e-7 is already enough to account for much of the 511 keV emission of the Galaxy.  A simple spherical accretion model predicts an emission profile highly peaked in the central bulge, consistent with INTEGRAL observations.  However, a realistic model of accretion with angular momentum would likely imply a more extended emission over the disk, with uncertainties depending on the B-field structure and turbulence in the galactic halo.

1304.0425
Analytic solutions for Navarro--Frenk--White lens models for low characteristic convergences
Dumet-Montoya, Caminha, Makler

NFW profile used to model G lenses; for low values of kappa_s << 1 of this model (galaxy and group mass scales), a high numerical precision is required in order to accurately compute several quantities in the SL regime.  An alternative for fast and accurate computations is to derive analytic approximations in this limit.  In this work, obtain analytic solutions for several lensing quantities for elliptical NFW and pseudo-elliptical NFW lens models.  Analytic solutions for the convergence and shear, etc.  Compute the deformation cross section.  Provide a simple expression for the ellipticity of the iso-convergence contours of the pseudo-elliptical models...  Conclude that the set of solutions derived here is generally accurate for kappa_s<0.1.  For low ellipticities, values up to kappa_s<0.18 allowed.  Mapping between PNFW and ENFW valid up to kappa_s~0.4.  The solutions derived in this work can be used to speed up numerical codes and ensure their accuracy in the low kappa_s regime, including applications to arc statistics and other strong lensing observables.