* Astronomy

Title: Hubble Space Telescope Imaging of the Ultra-Compact High Velocity Cloud AGC 226067: A stripped remnant in the Virgo Cluster
Author: D.J. Sand, A.C. Seth, D. Crnojevic, K. Spekkens, J. Strader, E. A. K. Adams, N. Caldwell, P. Guhathakurta, J. Kenney, S. Randall, J.D. Simon, E. Toloba, B. Willman

We analyse the optical counterpart to the ultra-compact high velocity cloud AGC 226067, utilizing imaging taken with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. The colour magnitude diagram of the main body of AGC 226067 reveals an exclusively young stellar population, with age ~7--50 Myr and [Fe/H]~-0.3, and is consistent with a distance of D approx 17 Mpc, suggesting an association with the Virgo cluster. A secondary stellar system located ~1.6' (~8 kpc) away in projection has a similar stellar population. The lack of an old red giant branch (\gtrsim 5 Gyr) is contrasted with a serendipitously discovered Virgo dwarf in the ACS field of view (Dw J122147+132853), and the total diffuse light from AGC 226067 is consistent with the luminosity function of the resolved ~7--50 Myr stellar population. The main body of AGC 226067 has a MV=-11.3±0.3, or M_stars=5.4±1.3 x 10^4 solar masses given the stellar population. We searched 20 deg2 of imaging data adjacent to AGC 226067 in the Virgo Cluster, and found two similar stellar systems dominated by a blue stellar population, far from any massive galaxy counterpart -- if this population has similar star formation properties as AGC 226067, it implies ~0.1 solar masses yr^-1 in Virgo intracluster star formation. Given its unusual stellar population, AGC 226067 is likely a stripped remnant and is plausibly the result of compressed gas from the ram pressure stripped M86 subgroup (~350 kpc away in projection) as it falls into the Virgo Cluster.

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