Day 904

Thursday.


1506.02729
Fast estimators for redshift-space clustering
Scoccimarro

Redshift-space distortions in galaxy surveys happen along the radial directions, breaking statistical translation invariance.  Construct estimators for radial distortions that, using only 7 FFTs of the overdensity fields for a given survey geometry, compute the PS monopole, quadrupole and hexadecapole, and generalize such estimators to the bispectrum.  The resulting algorithm is very efficient, e.g., for the BOSS survey requires about 3 minutes for ell=0,2,4 PS for scales up to k=0.3 h/Mpc and about 10 minutes for ell=0,2 bispectra for all scales and triangle shapes up to k=0.2 h/Mpc on a single core.  The speed and these estimators is essential as it makes possible to compute covariance matrices from large number of realizations of mock catalogs with realistic survey characteiristics, and paves the way for improved constraints of gravity on cosmo scales, inflation and galaxy bias.


1506.03085
Forming compact massive galaxies at z~2
van Dokkum, et al

Study a key phase in the formation of massive galaxies: the transition of SF galaxies into massive (M*~1e11 Msun), compact (r_e~1kpc) quiescent galaxies, which takes place from z~3 to z~1.5.  Use HST grim redshifts and extensive photometry in all 5 3D-HST/CANDELS fields, more than doubling the area used previously for such studies, and combine these data with Keck MOSFIRE and NIRSPEC spectroscopy.  First confirm that a population of massive, compact, SF galaxies exists at z~2, using K-band spectroscopy of 25 of these objects at 2.0<z<2.5.  They have a median NII/Halpha ratio of 0.6, are highly obscured with SFR(tot)/SFR(Halpha)~10, and have a large range of observe velocity dispersions.  Infer from the kinematics and spatial distribution of Halpha that the galaxies have rotating disks of ionized gas that are a factor of ~2 more extended than the stellar distribution.  By combining measurements of individual galaxies, find that the kinematics are consistent with a Keplerian fall-off from V_rot~500 km/s at 1 kpc to V_rot~250 km/s at 7kpc, and that the total mass out to this radius is dominated by the dense stellar component.  Next, study the size and mass evolution of the progenitors of compact massive galaxies.  Even though individual galaxies may have had complex histories with periods of compaction and mergers, show that the population of progenitors likely followed a simple inside-out growth track in the size-mass plane of d(log r_e) ~0.3 d(log (M_stars).  This mode of growth gradually increases the stellar mass within a fixed physical radius, and galaxies quench when they reach a stellar density or velocity dispersion threshold.  As shown in other studies, the mode of growth changes after quenching, as dry mergers take the galaxies on a relatively steep track in the size-mass plane.