How Was the Galactic Halo Formed? Quantifying Velocity Substructure in the Halo

Details How Was the Galactic Halo Formed? Quantifying Velocity Substructure in the Halo How Was the Galactic Halo Formed? Quantifying Velocity Substructure in the Halo

Aug 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999noao.prop..371o&link_type=abstract

NOAO Proposal ID #1999B-0371

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Scientific paper

What fraction of the galactic halo was formed by accretion of satellite galaxies? What is the total mass of the Galaxy? We now know that some of the halo was formed by accretion (see below for details), next we aim to quantify how much was accreted. We have completed photometry for 24 1-deg^2 fields in our photometric search for halo stars. We need followup spectroscopy to test for velocity substructure: interestingly, two of our WIYN/Hydra fields show evidence for a non-equilibrium halo. This result, with that of Majewski ηlof kinematic substructure at the NGP, is intriguing, because the stars in both fields are within 20 kpc of the Galaxy's center. Why is so much substructure seen where it should be quickly destroyed by the Galaxy's tidal field? Have several small satellites been accreted in the past Gyr or two? We need data in other fields to answer this question. We are applying for WIYN/Hydra time to obtain spectra in five more fields for ~350 halo stars with R< 30 kpc. Also, we are applying for 4m/RCSP time to observe the faint outer-halo giants and BHB stars in 3 fields. These stars will both probe the outer halo, where velocity substructure persists much longer, and will also provide important new constraints on the mass and shape of the Galaxy's dark halo.

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