Dissecting the Sub-Structured Halo

University Of Virginia Main Campus, Charlottesville VA

Investigators

Abstract

Dr. Steven Majewski (University of Virginia) and his team will undertake a suite of five major experiments that will both expand the census of known Milky Way halo tidal streams and exploit halo streams for the understanding of galaxy evolution, structure formation and dark matter (DM) on galaxy-scales. These experiments are (1) A study of the chemistry of halo tidal streams using echelle spectroscopy of stream stars at both optical and near-infrared wavelengths to verify the discovery of a metallicity gradient in the leading arm of the Sagittarius stream, (2) A study of the 3-D motions of stream stars contained in a ground-based proper motion survey of 54 near-equatorial Kapteyn Selected Area fields to derive stream orbits and constrain the shape and strength of the Milky Way potential, (3) Undertake a pilot study with the Green Bank Telescope of a sample of M-type giant stars in tidal streams to look for bright water masers that can be used for precision astrometry of tidal streams using the Very Large Baseline Array, (4) A spectroscopic follow-up to the photometric Grid Giant Star Survey, which has already identified a number of previously known and newly discovered halo substructures across both hemispheres of the sky, and (5) More fully characterize the spatial and radial velocity distributions of G and K giant stars in what look to be "classical" stellar halos discovered around the Large and Small Magellanic Clouds by this research group. The stellar component of our Galactic halo provides an important test-bed for theories of galaxy formation. The present "concordance", hierarchical DM cosmologies predict the presence of stellar streams as tidal remnants of accreted sub-halos. Finding and characterizing these streams thus provides crucial information to constrain the nature of the Cold DM-predicted merging history. These streams are also highly sensitive dynamical probes constraining the shape, strength and lumpiness of the halo of the Milky Way, and provide key insights into the chemical evolution of galaxies. A key aspect of this research is that it has been fueled primarily by student leadership and contributions at both the undergraduate and graduate level. Each experiment is being led or will be led by a different graduate student as part of their Ph.D. dissertation.