Day 674

Monday.

1406.1503
The luminosity and stellar mass functions of GRB host galaxies: insight into the metallicity bias
Trenti, Perna, Jiminez

Long-duration GRBs are powerful probes of the SFH of the universe, but the correlation between the two depends on the highly debated presence and strength of a metallicity bias.  To investigate this correlation, use a phenomenological model that successfully describes SFRs, luminosities and stellar masses of SF galaxies, and apply it to GRB production.  Predict the comoving GRB rate and luminosities/stellar masses of host galaxies depending on the presence (or absence) of a metallicity bias, highlighting that apparent conflicts among previous studies might disappear following a comprehensive data-model comparison.  Conclude that : (1) the best fitting model includes a moderate metallicity bias, broadly consistent with the large majority of the long-duration GRBs in metal-poor environments originating from a collapsar (~83%), but with a secondary contribution from a metal-independent production channel, such as binary evolution; (2) Because of the mass-metallicity relation of galaxies, the metal-independent channel becomes dominant at z<2, where hosts have higher metallicities and collapsars are suppressed.  This possibly explaines studies that find no clear evidence of a metal-bias based on low-z samples; (3) lower, but non-zero, efficiencies of the metal-independent GRB channel might be preferred following a comprehensive fit that includes metallicity of GRB hosts; (4) Overall, the optimal redshift range to investigate the GRB metallicity bias is 1.5<z<4, when the majority of SF galaxies have metallicities in the range ~0.1-1 Zsun; (5) careful data-model comparison is critical, and complicated by dust-absorption, which may hide SF in the most massive galaxies, but not necessarily the GRB explosion.  These findings are limited by the small size of complete samples of GRB host observations.

1406.1506
The ellipticity distribution of ambiguously blended objects
Dawson, Schneider, Tyson, Jee

Using overlapping fields with HST and Subaru imaging, identify a population of blended galaxies that would not be easily distinguished with ground-based monochromatic imaging alone, labeled 'ambiguous blends'.  For the depth targeted with the LSST, the ambiguous blend population is both large (~14%) and has a distribution of ellipticities that is markedly different from that of unblended objects [really?] in a way that will likely be important for the WL measurements.  Most notably, find that ambiguous blending results in a ~14% increase in shear noise (or ~12% decrease in the effective number density of galaxies, n_eft) due to 1) larger intrinsic ellipticity dispersion, 2) a scaling with the galaxy number density N_gal that is shallower than 1/sqrt(N_gal).  For the LSST Gold sample (i<25.3) there is a ~7% increase in shear noise (or ~7% decrease in n_eff).

1406.1592
Constraining photon mass by energy-dependent gravitational light bending
Qian

Test at a cosmological scale by looking at SL data available and an upper limit of 8.71e-39g on photon mass (previous mass upper limit: 1.2e-51g).  

1406.1718
The 1% concordance Hubble constant
Bennett, Larson, Weiland, Hinshaw

The determination of the Hubble constant has been a central goal in observational astrophysics for nearly 100 years.  Extraordinary progress has occurred in recent years on two fronts: the cosmic distance ladder measurements at low redshift and CMB measurements at high redshift.  This CMB is used to predict the current expansion rate through a best-fit cosmological model.  Complementary progress has been made with BAO measurements at relatively low redshifts.  While BAO data do not independently determine a Hubble constant, they are important for constraints on possible solution and checks on cosmic consistency.  A precise determination of the Hubble constant is of great value, but it is more important to compare the high and low redshift measurements to test the cosmological model.  Significant tension would suggest either uncertainties not accounted for in the experimental estimates, or the discovery of new physics beyond the standard model of cosmology.  In this paper, examine in detail the tension between the CMB, BAO, and cosmic distance ladder data sets.  Find that these measurements are consistent within reasonable statistical expectations, and there are combined to determine a best-fit Hubble constant of 69.6 pm 0.7 km/s/Mpc.  The combined data constrain the Hubble constant to `%, with no compelling evidence for new physics.

1406.1785
Direct detection of Black Holes via electromagnetic radiation
Sobrinho, Augusto

BHs emit radiation composed of photons, gravitons and, later in their lives, massive particles.  Explore the detection of such BHs with present day masses from 1e-22 Msun to 1e-11 Msun.  Conclude that in the visible and UV BHs can be directly detected at z<1e7 m while in the X-ray the distances might reach 1e8m (Earth-Moon distance) and in the gamma-ray, BHS might even be detected from as far as ~0.1 pc.    Suggest future space mission data to reach this goal.

1406.1787
Target allocation yields for massively multiplexed spectroscopic surveys with fibers
Saunders, et al

Present Simulated Annealing fiber-to-target allocation simulations for the proposed DESI and 4MOST massively multiplexed spectroscopic surveys, and for both Poisson and realistically clustered mock target samples.  Simulate both Echidna and theta-phi actuator designs, including the restrictions caused by the physical actuator characteristics during repositioning.  For DESI, with theta-phi actuators, used in 5 passes over the sky for a mock ELG/LRG/QSO sample, with matched fiber and target densities, a total target allocation yield of 89.3% was achieved, but only 83.7% for the high-priority Ly-alpha QSOs.  If Echidna actuators are used with the same pitch and number of passes, the yield increases by 5.7% and 16%, respectively.  Echidna also allows a factor-of-two increase in the number of close Lya QSO pairs that can be observed.  Echidna spine tilt causes a variable loss of throughput, with average loss being the same as the loss at the rms tilt.  With a natural tilt minimization scheme, find an rms tilt always close to 0.58 x maximum.  There is an additional but much smaller defocus loss, equivalent to an average defocus of 30 microns.  These tilt losses offset the gains in yield for Echidna, but because the survey strategy is driven by the higher priority targets, a clear survey speed advantage remains.  For 4MOST, high and low latitude sample mock catalogs were supplied by the 4MOST team, and allocations were carried out with the proposed Echidna-based positioned geometry.  At high latitudes, the resulting target completeness was 85.3% for LR  targets and 78.9% for HR targets.  At low latitude, the target completeness was 93.9% for LR targets and 71.2 % for HR targets.