[64.03] The Search for Stars in Compact High Velocity Clouds

AAS 207th Meeting, 8-12 January 2006
Session 64 ISM outside the Milky Way
Poster, Tuesday, 9:20am-6:30pm, January 10, 2006, Exhibit Hall

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[64.03] The Search for Stars in Compact High Velocity Clouds

R.E. Schulte-Ladbeck (University of Pittsburgh), U. Hopp (Universitats-Sternwarte Munchen)

We have been studying High Velocity Clouds to test the hypothesis that they are the ``missing" dwarf galaxies of the Local Group predicted in cosmological simulations. In this paper we present single-star optical and near-infrared photometry of a new sample of five Compact High Velocity Clouds, one of which produces Lyman series absorption on the sightline towards the Quasar Ton~S210. We do not detect a stellar component in any of the five clouds. By combining our data with previous results based on single-star photometry we now find that searches have been conducted toward 17 High Velocity Clouds; and in none of them was a resolved stellar population detected. There is a 50% chance of getting a null result if fewer than 4% of all High Velocity Clouds contain stars. The High Velocity Clouds thus represent an unlikely source to provide the ``missing" satellite galaxies of the Milky Way which are predicted in cosmological simulations of structure formation. This result, and other deep imaging surveys, now imply that the ``missing" satellites may not have simply been overlooked observationally, indicating that there is no easy way out of the substructure problem.

This study made use of data from the ESO VLT and from 2MASS. We were assisted in this project by our colleagues Dr. J.~Kerp and by B.~Cherinka. This study has been supported by a NASA ADP grant titled ``The Building Blocks of the Local Group or Testing Astrophysical Solutions to the Substructure Problem".

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