The Enigmatic (Almost) Dark Galaxy Coma P: Distance Measurement and Stellar Populations from HST Imaging. (arXiv:1901.07557v1 [astro-ph.GA])

The Enigmatic (Almost) Dark Galaxy Coma P: Distance Measurement and Stellar Populations from HST Imaging. (arXiv:1901.07557v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Brunker_S/0/1/0/all/0/1">Samantha W. Brunker</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+McQuinn_K/0/1/0/all/0/1">Kristen B. W. McQuinn</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Salzer_J/0/1/0/all/0/1">John J. Salzer</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cannon_J/0/1/0/all/0/1">John M. Cannon</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Janowiecki_S/0/1/0/all/0/1">Steven Janowiecki</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Leisman_L/0/1/0/all/0/1">Lukas Leisman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rhode_K/0/1/0/all/0/1">Katherine L. Rhode</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Adams_E/0/1/0/all/0/1">Elizabeth A. K. Adams</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ball_C/0/1/0/all/0/1">Catherine Ball</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dolphin_A/0/1/0/all/0/1">Andrew E. Dolphin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Giovanelli_R/0/1/0/all/0/1">Riccardo Giovanelli</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Haynes_M/0/1/0/all/0/1">Martha P. Haynes</a>

We present Hubble Space Telescope (HST) observations of the low surface
brightness (SB) galaxy Coma P. This system was first discovered in the Arecibo
Legacy Fast ALFA HI survey and was cataloged as an (almost) dark galaxy because
it did not exhibit any obvious optical counterpart in the available survey data
(e.g., Sloan Digital Sky Survey). Subsequent WIYN pODI imaging revealed an
ultra-low SB stellar component located at the center of the HI detection. We
use the HST images to produce a deep color-magnitude diagram (CMD) of the
resolved stellar population present in Coma P. We clearly detect a red stellar
sequence that we interpret to be a red giant branch, and use it to infer a tip
of the red giant branch (TRGB) distance of 5.50$^{+0.28}_{-0.53}$ Mpc. The new
distance is substantially lower than earlier estimates and shows that Coma P is
an extreme dwarf galaxy. Our derived stellar mass is only 4.3 $times$ 10$^5$
$M_odot$, meaning that Coma P has an extreme HI-to-stellar mass ratio of 81.
We present a detailed analysis of the galaxy environment within which Coma P
resides. We hypothesize that Coma P formed within a local void and has spent
most of its lifetime in a low-density environment. Over time, the gravitational
attraction of the galaxies located in the void wall has moved it to the edge,
where it had a recent “fly-by” interaction with M64. We investigate the
possibility that Coma P is at a farther distance and conclude that the
available data are best fit by a distance of 5.5 Mpc.

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