Day 940

Friday.


1508.01203
Discovery of two gravitationally lensed quasars in the Dark Energy Survey
Agnello, Treu, ... et al

Present spectroscopic confirmation of 2 new lensed quasars via 6.5 Magellan/Baade Telescope.  The lens candidates have been selected from DES and WISE based on their multi-band photometry and extended morphology in DES images.  Images of DES J0115-5244 show 2 blue point sources at either side of a red galaxy.  The long-slit data confirm that both point sources are images of the same quasar at z_s=1.64.  The Einstein Radius estimated from the DES images is 0.51".  DES J2200+0110 is in the area of overlap between DES and SDSS.  Two blue components are visible in the DES and SDSS images.  The SDSS fiber spectrum shows a quasar component at z_s=2.38 and absorption compatible with Mg II and Fe II at z_l=0.799, which is possibly associated with the foreground lens galaxy.  The long-slit Magellan spectra show that the blue components are resolved images of the same quasar.  The Einstein Radius is 0.68" corresponding to an enclosed mass of 1.6e11 Msun.  Three other candidates were observed and rejected, two being low-z pairs of starburst galaxies, and one being a quasar behind a blue star.  These first confirmation results provide an important empirical validation of the data-mining and model-based selection that is being applied to the entire DES data set.


1508.01204
The galaxy UV luminosity function before the epoch of reioinzation
Mason, Trenti, Treu

Present a model for the evolution of the galaxy UV LF across cosmic time where SF is linked to the assembly of DM halos under the assumption of halo mass dependent, but redshift independent, star formation efficiency.  This model improves on previous work by introducing a new self-consistent treatment of the halo SF history, which allows making predictions at z>10 (loopback time <500 Myr), when growth is rapid.  With a calibration at a single redshift to set the stellar to halo mass ratio, and no further degrees of freedom, the model captures the evolution of the UV LF over all the available observations (0<z<10).  The significant drop in the luminosity density of currently detectable galaxies beyond z~8 is explained by a shift of star formation toward less massive, fainter galaxies.  Assuming that star formation proceeds down to atomic cooling halos, derive a reionization optical depth tau=0.056±0.01 fully consistent with the latest Planck measurement, and implying that the universe is fully recognized at z=7.84±0.98.  In addition, the model naturally produces smoothly rising SFHs for galaxies with L<L* in agreement with observations and detailed hydro sims.  Before the epoch of reionization at z>10, predict the LF to remain well-described by a Schechter function, but with an increasingly steep faint-end slope (alpha~-3.5 at z~16).  Finally, construct detailed forecasts with JWST and WFIRST, including the boost from gravitational lensing magnification bias in blank fields, and predict that galaxies out to z~14 will be observed.  However, galaxies at z>15 will likely be accessible to JWST and WFIRST only through the assistance of strong lensing magnification.