Michael Schneider

and 3 more

This is to organize activities and research project ideas for an intrinsic alignments subgroup within weak lensing. Several of us met at AAS 223 on January 7, 2014 and made a plan to organize joint IA work for DESC science. APPROACHES FOR MITIGATING IAS - Mocks - “paint” galaxies into N-body cosmological simulations - Nulling - cancel out the IA contribution using the knowledge of the redshift distribution in the lensing kernel - Self-calibration - use the cross-correlation of clustering and shear to learn the form of the IA contributions in the data - Model fitting - define a parameterized model for the IA and marginalize over parameters. This could range from a simple model like the NLA model, with one (or a few parameters), to a much more complex halo model that includes numerous parameters for satellite occupation, IA, mass-light ratio, etc. This latter approach is similar to recent work being done to combine lensing and clustering measurements (e.g./ the work of Cacciato, More, and van den Bosch). EUCLID is likely to pursue an inclusive modeling approach. PROJECT IDEAS - Use the halo model to fit the w_g+(theta) measurements presented at the Pittsburgh 2013 DESC meeting. - The NLA model is becoming popular, but it is an ad-hoc model that should be treated with caution. A simple but more robust model should be developed. This could come from consistent analytic treatment of nonlinear effects (Blazek is currently developing this approach) and/or halo-matter cross-correlation from simulations (Schneider is developing this approach). to the above item: in the context of a given model, IA parameters could be expressed in terms of more physically meaningful quantities. For example, the C_1 parameter of the (N)LA model could be derived as an integral over central and satellite angular alignment with their DM halos, etc. Such an approach could allow us to place priors on IA parameters through understanding the underlying galaxy/halo physics. Alternatively, this could allow us to constrain galaxy/halo physics from IA measurements.