Day 389

Monday.

1303.3584
The spatial extent and distribution of star formation in 3d-HST mergers at z~1.5
Schmidt, Rix, ... van Dokkum, ...et al

Analysis of the spatial distribution of SF in a sample of 60 visually identified galaxy merger candidates at z>1.  Use NIR slitless spectra from 3d-HST which produce Ha or [OIII] emission line maps as proxies for SF maps.  Find: detectable SF can occur in one or both galaxy centers, or in tidal tails.  Most common (58%): SF is largely concentrated in a single, compact region, coincident with the center of the merger components.  No correlations between SF morphology and redshift, total stellar mass, or SFR are found.  Hydrosim implies SF should be detectable in both merger components, when the gas fractions of the individual components are the same----hence suggesting that z~1.5 mergers typically occur between galaxies whose gas fractions, masses, and/or SFR are distinctly different from one another.

1303.3586
The limits of subhalo abundance matching
Guo, White (Simon)

SHAM inserts galaxies into DM only sims of the growth of cosmic structure in a way the requires minimal assumptions about galaxy formation.  Galaxies placed at the potential minimum of each distinct self-bound sub halo with a luminosity which is monotonically increasing function of the maximum mass (or circular velocity) attained over the subhalo's earlier history.  Galaxy and subhalo properties are linked by matching model and observed luminosity functions.  Simulated structures can then be compared in detail with observation, for example, through galaxy correlation statistics, group catalogues, or gg lensing.  Physically meaningful results require the abundance and clustering of subhaloes to be unaffected by numerical resolution.  Use Millennium and M-II simulations with subhaloes defined using the SUBFIND algorithm to explore the limitations imposed by this requirement.  Correlation statistics on scales between 200 kpc and 2 Mpc converge to within 20% only for subhaloes with maximum past masses corresponding to 1000 simulation particles or moer.  This is substantially above the mass limit to which results are quoted in recent SHAM analyses.  Detailed galaxy formation simulations based on SAM techniques converge to much lower mass, because they follow galaxies even after their associated subhaloes have been tidally disrupted.

1303.3588
Improving the precision of time-delay cosmography with observations of galaxies along the line of sight
Green, Suyu, Treu, Hilbert, ... Marshall, ... Blandford, Bradac, Koopmans

In order to use SL time delays to measure precise and accurate cosmological parameters the effects of mass along the LoS must be taken into account.  Present a method to achieve this by constraining the PDF of the effective LoS convergence k_ext.  The method is based on matching the observed overdensity in the weighted number of galaxies to that found in mock catalogs with k_ext obtained by ray-tracing through structure formation simulations.  Explore weighting schemes based on projected distance, mass, luminosity, and redshift.  These additional information reduces the uncertainty of k_ext from sigma_k [>]0.06 to 0.04 for very overdense LoS like that of the system B1608+656.  For more common LoS, sigma_k is reduced to <0.03, corresponding to an uncertainty of <3% on distance.  This uncertainty has comparable effects on cosmological parameters to that arising from the mass model of the deflector and its immediate environment.  Photometric redshifts based on griK photometries [which survey is this?] are sufficient to constrain k_ext almost as well as with spectroscopic redshifts.  As an illustration, apply method to the B1608+656 system.  The most reliable k_ext esitmator gives sigma_k=0.047 down from 0.065 using only galaxy counts.  Although deeper multi-band observations of the field of B1608+656 are necessary to obtain a more precise estimate, conclude that griK photometry, in addition to spectroscopy to characterize the immediate environment, is an effective way to increase the precision of time-delay cosmography.  

1303.3663
Measuring gravitational redshifts in galaxy clusters
Kaiser

Wojtak+ stacked 78k clusters from SDSS in z-space; find a small net blue-shift for the cluster galaxies relative to the BCG, which agrees quite well with the gravitational redshift from GR.  Zhao+ have pointed out that, in addition to the gravitational z, one would expect to see transverse Doppler (TD) redshifts, and that these two effects are generally of the same order.  Show that there are other corrections that are also of the same order of magnitude.  The fact that galaxies are observed in our past light cone results in a bias such that more of the galaxies observed are moving away from us in the frame of the cluster than are moving towards us.  This causes the observed average redshift to be <dz>=-<\Phi>+<beta^2>/2 + <beta_x^2>, with beta_x the LoS velocity.  That is if we average over galaxies with equal weight.  If the galaxies in each cluster are weighted by their fluence [flux], or equivalently if we do not resolve the moving sources, and make an average of the mean z giving equal weight per photon, the observed z is then opposite to the usual transverse Doppler effect.  In the WHH experiment, the weighting is a step-function because of the flux-limit for inclusion in the spectroscopic sample and the result is different again, and depends on the details of the LF and the SEDs of the galaxies.  Including these effects substantially modifies the blue-shift profile.  Identify some potential biases in the dynamical analysis of stacked clusters.  Show that in-fall and out-flow have very small effect over the relevant range of impact parameters.

1303.3705
Asteroid 2012 XE133, a transient companion to Venus
de la Fuente Marcos, de la Fuente Marcos

Venus horseshoe orbit companions!  Animations (somewhere, but not here)!

1303.3808
THe VIMOS public extragalactic redshift survey (VIPERS).  A precise measurement of the galaxy stellar mass function and the abundacne of massive galaxies at redshifts 0.5<z<1.3
Davidzon, ... Coupon, Ilbert, Arnouts, ... et al

Measure the evolution of galaxy stellar mass function from z=1.3 to 0.5 using 53k redshifts of VIPERS.  At the epoch sampled by VIPERS, massive galaxies had already assembled most of their stellar mass.  (VIPERS data allow determination with accuracy the high-mass tail of the galaxy stellar mass function.)  Apply a photometric classification in the (U-V) rest-frame color to compute the MF of blue and red galaxies, finding evidence for the evolution of their contribution to the total number density budget: the transition mass above which red galaxies dominate is found to be about 1e10.4 Msun at z=0.55 and evolves proportional to (1+z)^3.  Able to trace separately the evolution the number density of blue and red galaxies with masses above 1e11.4 Msun, in a mass range barely studied in previous work due to the small volumes surveyed.  Find that for such large masses, red galaxies show a milder evolution with z, when compared to objects at lower masses.  At the same time, detect a population of similarly massive blue galaxies, which are no longer detectable below z=0.7. [Does that mean that blue massive galaxies don't exist at z<0.7?] These results show the improved statistical power of VIPERS data, and give initial promising indications of mass-dependent quenching of galaxies at z~1.