Detection of an Optical Counterpart to the ALFALFA Ultra-compact High Velocity Cloud AGC 249525

William Janesh; Katherine L. Rhode; John J. Salzer; Steven Janowiecki; Elizabeth A. K. Adams; Martha P. Haynes; Riccardo Giovanelli; John M. Cannon

doi:10.3847/2041-8213/aa62a1

arXiv · 1702.07282

Detection of an Optical Counterpart to the ALFALFA Ultra-compact High Velocity Cloud AGC 249525

William Janesh·Katherine L. Rhode·John J. Salzer·Steven Janowiecki·Elizabeth A. K. Adams·Martha P. Haynes·Riccardo Giovanelli·John M. Cannon

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Abstract

We report on the detection at $>$98% confidence of an optical counterpart to AGC 249525, an Ultra-Compact High Velocity Cloud (UCHVC) discovered by the ALFALFA blind neutral hydrogen survey. UCHVCs are compact, isolated HI clouds with properties consistent with their being nearby low-mass galaxies, but without identified counterparts in extant optical surveys. Analysis of the resolved stellar sources in deep $g$- and $i$-band imaging from the WIYN pODI camera reveals a clustering of possible Red Giant Branch stars associated with AGC 249525 at a distance of 1.64$\pm$0.45 Mpc. Matching our optical detection with the HI synthesis map of AGC 249525 from Adams et al. (2016) shows that the stellar overdensity is exactly coincident with the highest-density HI contour from that study. Combining our optical photometry and the HI properties of this object yields an absolute magnitude of $-7.1 \leq M_V \leq -4.5$, a stellar mass between $2.2\pm0.6\times10^4 M_{\odot}$ and $3.6\pm1.0\times10^5 M_{\odot}$, and an HI to stellar mass ratio between 9 and 144. This object has stellar properties within the observed range of gas-poor Ultra-Faint Dwarfs in the Local Group, but is gas-dominated.

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William Janesh, Katherine L. Rhode, John J. Salzer, Steven Janowiecki, Elizabeth A. K. Adams, Martha P. Haynes, Riccardo Giovanelli, John M. Cannon. 2017-02-23. Detection of an Optical Counterpart to the ALFALFA Ultra-compact High Velocity Cloud AGC 249525. https://doi.org/10.3847/2041-8213/aa62a1

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