A Comprehensive Archival Search for Counterparts to Ultra-Compact High Velocity Clouds: Five Local Volume Dwarf Galaxies

D. J. Sand, D. Crnojević, P. Bennet, B. Willman, J. Hargis, J. Strader, E. Olszewski, E. J. Tollerud, J. D. Simon, N. Caldwell, P. Guhathakurta, B. L. James, S. Koposov, B. McLeod, N. Morrell, M. Peacock, R. Salinas, A. C. Seth, D. P. Stark, E. Toloba

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

We report five Local Volume dwarf galaxies(two of which are presented here for thefirst time)uncovered duringa comprehensive archival search for optical counterparts to ultra-compact high-velocity clouds(UCHVCs). TheUCHVC population of HI clouds are thought to be candidate gas-rich, low-mass halos at the edge of the LocalGroup and beyond, but no comprehensive search for stellar counterparts to these systems has been presented.Careful visual inspection of all publicly available optical and ultraviolet imaging at the position of the UCHVCsrevealed six blue, diffuse counterparts with a morphology consistent with a faint dwarf galaxy beyond the LocalGroup. Optical spectroscopy of all six candidate dwarf counterparts show thatfive have an Hα-derived velocityconsistent with the coincident HI cloud, confirming their association; the sixth diffuse counterpart is likely abackground object. The size and luminosity of the UCHVC dwarfs is consistent with other known Local Volumedwarf irregular galaxies. The gas fraction(MMHI star)of thefive dwarfs are generally consistent with that of dwarfirregular galaxies in the Local Volume, although ALFALFA-Dw1(associated with ALFALFA UCHVCHVC274.68+74.70–123)has a very highMMHI star∼40. Despite the heterogenous nature of our search, wedemonstrate that the current dwarf companions to UCHVCs are at the edge of detectability due to their low surfacebrightness, and that deeper searches are likely tofind more stellar systems. If more sensitive searches do not revealfurther stellar counterparts to UCHVCs, then the dearth of such systems around the Local Group may be in conflictwithΛCDM simulations.
Original languageEnglish
JournalAstrophysical Journal
Publication statusPublished - 10 Jun 2015

Keywords / Materials (for Non-textual outputs)

  • astro-ph.GA


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