Day 915

Tuesday.


1506.08222
Galaxy and mass assembly (GAMA): end of survey report and data release 2
Liske, et al

The GAMA survey is one of the largest contemporary spectroscopic surveys of low-z galaxies. Covering an area of ~286 deg^2 (split among five survey regions) down to a limiting magnitude of r<19.8 mag, they have collected spectra and reliable redshifts for 238k objects using the AAOmega spectrograph on the AAT.  In addition, they have assembled imaging data from a number of independent surveys in order to generate photometry spanning the wavelength range 1 nm-1m.  Report on the recently completed spectroscopic survey and present a series of diagnostics to assess its final state and the quality of the redshift data.  Also describe a number of survey aspects and procedures, or updates thereof, including changes to the input catalogue, redshifting and re-redshifting, and the derivation of UV, optical and NIR photometry.  Finally, present the second public release of GAMA data.  In this release, provide input catalogue and targeting information, spectra, z, UV, optical and NIR photometry, single-component Sersic fits, stellar masses, Ha-derived SFRs, environment information, and group properties for all galaxies with r<19.0 mag in two of the survey regions, and for all galaxies with r<19.4 mag in a 3rd region (72,225 objects in total).  The database serving these data is available online.


1506.08359
Detecting stellar spots through polarimetry observations of microlensing events in caustic-crossing
Sajadian

Investigate if gravitational microlensing can magnify the polarization signal of a stellar spot and make it be observable.  A stellar spot on a source star of microlensing makes polarization signal through two channels of Zeeman effect and breaking circular symmetry of the source surface brightness due to its temperature contrast.  First explore the characteristics of perturbations in polarimetric microlensing during caustic-crossing of a binary lensing as follows:  (a) the cooler spots over the Galactic bulge sources have the smaller contributions in the total flux, although they have stronger B-fields.  (b) the maximum deviation in the polarimetry curve due to the spot happens when the spot is located near the source edge and the source spot is first entering the caustic whereas the maximum photometric deviation occurs for the spots located at the source center.  (c) There is a (partial) degeneracy for indicating spot's size, its temperature contrast and its magnetic induction from the deviations in light or polarimetric curves.  (d) if the time when the photometric deviation due to spot becomes zero (between positive and negative deviations) is inferred from microlensing light curves, the magnification factor of the spot can be indicated, characterizing the spot properties except its temperature contrast.  The stellar spots alter the polarization degree as well as strongly change its orientation which gives some information about the spot position.  Although, the photometry observations are more efficient in detecting stellar spots than the polarimetry ones, but polarimetry observations can specify the magnetic field of the source spots.


1506.08642
Galactic archeology - requirements on survey spectrographs
Feltzing

Galactic archeology is about exploring the MW as a galaxy by, mainly, using its (old) stars as tracers of past events and thus figure out the formation and evolution of the Galaxy.  Briefly outline some of the key scientific aspects of Galactic Archeology and then discuss the associated instrumentations.  Gaia will forever change the way this subject is approached.  However, Gaia on its own is not enough.  Ground-based complementary spectroscopy is necessary to obtain full phase-space information and elemental abundances for stars fainter than the top few percent of the bright part of the Gaia catalogue.  Review the requirement on instrumentation for Gaia follow-up that Galactic Archeology sets.  In particular, discuss the requirement on radial velocity and elemental abundance determination, including a brief look at potential pit-falls in the abundance analysis (e.g., NLTE, atomic diffusion).  This contribution also provides a non-exhaustive comparison of the various current and future spectrographs for Galactic Archeology.  Finally, discuss the needs for astrophysical calibrations for the surveys and inter-survey calibrations.


1506.08730
The impact of intrinsic alignment on current and future cosmic shear surveys
Krause, Eifler, Blazek

IA of source galaxies is one of the major astrophysical systematics for ongoing and future WL surveys.  This paper presents the first forecasts of the impact of IA on cosmic shear measurements for current and future surveys (DES, Euclid, LSST, WFIRST) using simulated likelihood analyses and realistic covariances that include higher-order moments of the density field in the computation.  Consider a range of possible IA scenarios and test mitigation schemes, which parameterize IA by the fraction of red galaxies, normalization, luminosity and redshift dependence of the IA signal (for a subset, consider joint IA and photo-z uncertainties). Compared to previous studies, find smaller biases in time-dependent DE models if IA is ignored in the anslysis; the amplitude and significance of these biases vary as a function of survey properties (depth, statistical uncertainties), luminosity function, and IA scenario: due to its small statistical errors and relatively shallow observing strategy Euclid is significantly impacted by IA.  LSST and WFIRST benefit from their increased survey depth, while the larger statistical errors for DES increase IA's relative impact on cosmological parameters.  The proposed IA mitigation scheme removes parameter biases due to IA for DES, LSST, and WFIRST even if the shape of the IA PS is only poorly known; successful IA mitigation for Euclid requires more prior information.  Explore several alternative IA mitigation strategies for Euclid; in the absence of alignment of blue galaxies, recommend the exclusion of red (IA contaminated) galaxies in cosmic shear analyses.  Find that even a reduction of 20% fin the number density of galaxies only leads to a 4-10% loss in cosmological constraining power.