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Identifying galaxy candidates in WSRT HI imaging of ultra-compact high velocity clouds

Submitter: Betsey Adams
Description: Ultra-compact high velocity clouds (UCHVCs) are isolated HI clouds detected in the ALFALFA HI survey with no optical counterpart in current optical surveys. They are intriguing objects because they are good candidates to represent gas-rich dark matter halos with a negligible stellar content. In order to address this hypothesis, an international team led by Betsey Adams and including Tom Oosterloo, observed twelve UCHVCs at higher angular resolution with the Westerbork Synthesis Radio Telescope (WSRT). The WSRT observations revealed that two objects, with a potential third, are the good galaxy candidates. The other UCHVCs are likely clouds of gas associated with our own Milky Way. The best galaxy candidates had the highest column density values in the ALFALFA data; this lesson will be used to select the best UCHVCs for further studies.

The image above shows one of the good galaxy candidates (left) compared to one of the objects that is likely associated with our own Milky Way (right). The top and bottom rows are at two different angular resolutions. The contours indicate the distribution of HI gas and the colors the velocity motion of the gas. The good galaxy candidates have a smooth distribution of gas at higher angular resolution and show ordered velocity motion. This velocity motion indicates that the gas could be rotating in a dark matter halo. For a range of plausible distances, the candidate galaxies have rotation velocities of 8-15 km/s, HI masses of 0.6-50 x 10^5 Msun, HI radii of 0.3-2 kpc, and dynamical masses of 2-20 x 10^7 Msun. Future surveys with Apertif, a new phased array feed for WSRT, will produce data like that pictured above, allowing the properties of these marginal galaxies to be studied.

You can find more details in Identifying galaxy candidates in WSRT HI imaging of ultra-compact high velocity clouds Elizabeth A. K. Adams, et al. 2016, A&A in press, http://arxiv.org/abs/1609.05377
Copyright: Betsey Adams
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