On the characterization of the Galactic warp in the Gaia era

¹ Dept. d'Astronomia i Meteorologia, Institut de Ciències del Cosmos, Universitat de Barcelona, IEEC, Martí i Franquès 1, 08028 Barcelona, Spain
² Instituto de Astronomia, UNAM, Apartado Postal 877, 22860 Ensenada, B.C., Mexico
³ Instituto de Astrofśica de Canarias, 38205 La Laguna, Tenerife, Spain

Abstract

We explore the possibility of detecting and characterising the warp of the stellar disc of our Galaxy using the synthetic Gaia data and the UCAC4 proper motion catalogue. We develop a new kinematic model for the galactic warp. We generate random realisations of test particles which evolve in a realistic Galactic potential warped adiabatically to various final configurations. The Gaia selection function, its errors model and a realistic 3D extinction map are applied to mimic three tracer populations: OB, A and Red Clump stars. A family of Great Circle Cell Counts (GC3) methods is used. They are ideally suited to find the tilt and twist of a collection of rings, which allow us to detect and measure the warp parameters. Moreover, We look for the kinematic signature of the warp in the μ_b proper motions of stars as a function of galactic longitude. Using the UCAC4 proper motions, we do not obtain a similar trend as the one we expect from our warp model. We explore a possible source of this discrepancy in terms of systematics caused by a residual spin of the Hipparcos celestial reference frame (HCRF) with respect to the extra-galactic inertial one.