Day 802

Tuesday.

1412.2132
The kiloparsec-scale star formation law at redshift 4: wide-spread, highly efficient star formation in the dust-obscured starburst galaxy GN20
Hodge et al

High-resolution 880um (rest-frame FIR) continuum emission in the z=4.05 sub millimeter galaxy GN20 resolve the obscured SF in this unlensed galaxy on scales of 2.1x1.3 kpc (0.3"x0.2").  The observations reveal a bright dusty starburst centered on the cold molecular gas reservoir and showing a bar-like extension along the major axis.  The striking anti-correlation with the HST/WFC3 imaging suggests that the copious dust surrounding the starburst heavily obscures the rest-frame UV/optical emission.  A comparison with 1.2mm PdBI continuum data reveals no evidence for variations in the dust properties across the source within the uncertainties, consistent with extended SF, and the peak SFR surface density 119pm8 Msun/yr/kpc2 implies that the SF in GN20 remains sub-Eddington on scales down to 3 kpc2.  Find that the SF efficiency is highest in the central regions of GN20, leading to a resolved SF law with a power law slope of 2.1, and that GN20 lies above the sequence of normal SF disks, implying that the dispersion in the SF law is not due solely to morphology or choice of conversion factor.  These data extend previous evidence for a fixed SF efficiency per free-fall time to include the SF medium on ~kpc-scales in a galaxy 12 Gyr ago.

1412.2137
Evidence for the inside-out growth of the stellar mass distribution in galaxy clusters since z~1
van der Burg, Hoekstra, et al

Study the radial number density and stellar mass density distributions of satellite galaxies in a sample of 60 massive clusters at 0.04<z<0.26 from MENeaCS and CCCP.  In addition to ~10k spectroscopically confirmed member galaxies, use deep ugri-band imaging to estimate photometric z and stellar masses, and then statistically subtract fore- and background sources using data from the COSMOS survey.  Measure the galaxy number density and stellar mass density distributions in logarithmically spaced bins over 2 orders of magnitude in radial distance from the BCGs.  For projected distances in the range 0.1<R/R200<2.0, find that the stellar mass distribution is well-described by an NFW profile with a concentration of c=2.03pm0.20.  However, at smaller radii measure a significant excess in the stellar mass in satellite galaxies of about 1e11 Msun per cluster, compared to these NFW profiles.  Obtain good fits to generalized NFW profiles with free inner slopes, and to Einasto profiles.  To examine how clusters assemble their stellar mass component over cosmic time, compare this local sample to the GCLASS cluster sample at z~1, which represents the approximate progenitor sample of the low-z clusters.  This allows for a direct comparison, which suggests that the central parts (R<0.4 Mpc) of the stellar mass distributions of satellites in local galaxy clusters are already in place at z~1, and contain sufficient excess material for further BCG growth.  Evolving towards z=0, clusters appear to assemble their stellar mass primary onto the outskirts, making them grow in an inside-out fashion.
1412.2141
Galaxy and mass assembly (GAMA): the galaxy luminosity function within the cosmic web
Eardley, Peacock, et al

Investigate the dependence of the galaxy LF on geometric environment within GAMA.  Find a significant variation in the LF of galaxies between different geometric environments; the normalization, characterized by phi* in Schechter function fit, increases by an order of magnitude from voids to knots.  The turnover magnitude, characterized by M*, brightens by approximately 0.5 mag from voids to knots.  However, show that the observed modulation can be entirely attributed to they direct local-density dependence.  Therefore find no evidence of a direct influence of the cosmic web on the galaxy luminosity function.


1412.2208
Combining spectroscopic and photometric surveys using angular cross-correlations I: Algorithm and modeling
Eriksen, Gaztanaga

WL clustering is studied using angular coordinates, while RSD and BAO use 3d coordinates, which requires a model dependent conversion of angles and redshifts into comoving distances.  Explore modeling multi-tracer galaxy clustering (of WL, BAO and RSD), using only 2d cross-correlations in thin z bins.  This involves evaluating many thousands cross-correlations, each a multidimensional integral, which is computationally demanding.  Present a new algorithm that performs these calculations as matrix operations.  Nearby narrow redshift bins are intrinsically correlated, which can be used to recover the full (radial) 3d information.  Show that the Limber approximation does not work well for this task.  In the exact calculation, both the clustering amplitude and the RSD effect increase when decreasing the redshift bin width.  For narrow bins, the cross-correlations has a larger BAO peak than the auto-correlation because smaller scales are filtered out by the radial z separation.  Moreover, the BAO peak shows a second (ghost) peak, shifted to smaller angle.  Explore how WL, RSD and BAO contribute to the cross-correlations as a function of the redshift bin width and present a first exploration of non-linear effects and signal-to-noise ratio on these quantities.  This illustrates the new approach to clustering analysis provides new insights and is potentially viable in practice.

1412.2529
Far-infrared excess emission as a tracer of disk-halo interaction
Lenz, Kerp, ... et al

Given the current and past SF in the MW in combination with the limited gas supply, the re-fuelling of the reservoir of cool gas is an important aspect of Galactic astrophysics.  The infall of H_i halo clouds can, among other mechanisms, contribute to solving this problem.  Study the intermediate-velocity cloud IVC135+54 and its spatially associated high-velocity counterpart to look for signs of a past or ongoing interaction.  Using the Effelsberg-Bonn H_i Survey data, investigate the interplay of gas at different velocities.  In combination with FIR Planck and IRIS data, extended this study to instestellar dust and used the correlation of the data sets to infer information on the dark gas.  The velocity structure indicates a strong compression and deceleration of the infalling HVC, associated with FIR excess emission in the intermediate-velocity cloud.  This excess emission traces molecular hydrogen, confirming that IVC135+54 is one of the very few molecular halo clouds.  The high dust emissivity of IVC135+54 with respect to the local gas implies that it consists of disk material and does not, unlike the HVC, have an extragalactic origin.  Based on the velocity structure of the HVC and the dust content of the IVC, a physical connection between them appears to be the logical conclusion.  Since this is not compatible with the distance difference between the two objects, conclude that this particular HVC might be much closer to us than complex C.  Alternatively, the indicators for an interaction are misleading and have another origin.