Day 1180

Wednesday.

1611.00008
Red nuggets grow inside-out: evidence from gravitational lensing
Oldham, et al

Present a new sample of SL systems where both the FG lenses and BG sources are early-type galaxies.  Using imaging from HST/ACS and Keck/NIRC2, model the surface brightness distributions and show that the sources form a distinct population of massive compact galaxies at 0.4<z<0.7, lying systematically below the size-mass relation of the global elliptical galaxy population at those redshifts.  These may therefore represent relics of high-z red nugget or their partly-evolved descendants.  Exploit the magnifying effect of lensing to investigate the structural properties, stellar masses and stellar populations of these objects with a view to understanding their evolution.  Model these objects parametrically and find that they generally require two Sersic components to properly describe their light profiles, with one more spheroidal component alongside a more envelope-like component, which is slightly more extended though still compact.  This is consistent with the hypothesis of the inside-out growth of these objects via minor mergers.  Also find that the sources can be characterized by red-to-blue colour gradients as a function of radius which are stronger at low z -- indicative of ongoing accretion -- but that their environments generally appear consistent with that of the general elliptical galaxy population, contrary to recent suggestions that these objects are predominantly associated with clusters.


1611.00036
The DESI Experiment Part I: science, targeting and survey design
DESI collaboration

DESI (Dark Energy Spectroscopic Instrument) is a Stage IV ground-based DE experiment that will study BAO and the growth of structure through z-space distortions with a wide-area galaxy and quasar redshift survey.  To trace the underlying DM distribution, spectroscopic target will be selected in 4 classes from imaging data.  It will measure luminous red galaxies up to z=1.0.  To probe the Universe out to even higher z, DESI will large bright [OII] emission line galaxies up to z=1.7.  Quasars will be targeted both as direct tracers of the underlying DM distribution and, at higher redshifts (2.1<z<3.5), for the Ly-alpha forest absorption features in their spectra, which will be used to trace the distribution of neutral hydrogen.  When moonlight prevents efficient observations of the fact targets of the baseline survey, DESI will conduct a magnitude-limited Bright Galaxy Survey comprising approximately 10 million galaxies with a median z~0.2.  In total, more than 30 million galaxy and quasar redshifts will be obtained to measure the BAO feature and determine the matter power spectrum, including redshift space distortions.