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

Abstract

We report five Local Volume dwarf galaxies (two of which are presented here for the first time) uncovered during a comprehensive archival search for optical counterparts to ultra-compact high velocity clouds (UCHVCs). The UCHVC population of HI clouds are thought to be candidate gas-rich, low mass halos at the edge of the Local Group 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 UCHVCs revealed six blue, diffuse counterparts with a morphology consistent with a faint dwarf galaxy beyond the Local Group. Optical spectroscopy of all six candidate dwarf counterparts show that five have an H$\alpha$-derived velocity consistent with the coincident HI cloud, confirming their association, the sixth diffuse counterpart is likely a background object. The size and luminosity of the UCHVC dwarfs is consistent with other known Local Volume dwarf irregular galaxies. The gas fraction ($M_{HI}/M_{star}$) of the five dwarfs are generally consistent with that of dwarf irregular galaxies in the Local Volume, although ALFALFA-Dw1 (associated with ALFALFA UCHVC HVC274.68+74.70$-$123) has a very high $M_{HI}/M_{star}$$\sim$40. Despite the heterogenous nature of our search, we demonstrate that the current dwarf companions to UCHVCs are at the edge of detectability due to their low surface brightness, and that deeper searches are likely to find more stellar systems. If more sensitive searches do not reveal further stellar counterparts to UCHVCs, then the dearth of such systems around the Local Group may be in conflict with $\Lambda$CDM simulations.

18 pages, 4 tables, 4 figures, ApJ Accepted

References in corpus (16)

• Updated Nearby Galaxy Catalog
• MegaPipe: the MegaCam image stacking pipeline at the Canadian Astronomical Data Centre
• The GALEX Ultraviolet Virgo Cluster Survey (GUViCS). IV: The role of the cluster environment on galaxy evolution
• The Local Group dwarf Leo T: HI on the brink of star formation
• Too Many, Too Few, or Just Right? The Predicted Number and Distribution of Milky Way Dwarf Galaxies
• The structural properties and star formation history of Leo T from deep LBT photometry
• A Catalog of Ultra-compact High Velocity Clouds from the ALFALFA Survey: Local Group Galaxy Candidates?
• The ALFALFA "Almost Darks" Campaign: Pilot VLA HI Observations of Five High Mass-to-Light Ratio Systems
• Discovery of a close pair of faint dwarf galaxies in the halo of Centaurus A
• Stripped gas as fuel for newly formed HII regions in the encounter between VCC1249 and M49: a unified picture from NGVS and GUViCS
• Discovery of a new faint dwarf galaxy associated with NGC 253
• ALFALFA Discovery of the Nearby Gas-rich Dwarf Galaxy Leo P. V. Neutral Gas Dynamics and Kinematics
• Two Local Volume Dwarf Galaxies Discovered in 21 cm Emission: Pisces A and B
• A new isolated dSph galaxy near the Local Group
• AGC198606: A gas-bearing dark matter minihalo?
• Searching for Stars in Compact High-Velocity Clouds. II

Cited by in corpus (17)

• Discovery of diffuse dwarf galaxy candidates around M101
• The properties of "dark" ΛCDM halos in the Local Group
• Resolved Dwarf Galaxy Searches within ~5 Mpc with the Vera Rubin Observatory and Subaru Hyper Suprime-Cam
• Tucana B: A Potentially Isolated and Quenched Ultra-faint Dwarf Galaxy at D$\approx$1.4 Mpc
• Galaxy And Mass Assembly (GAMA): detection of low-surface-brightness galaxies from SDSS data
• HST Imaging of the Local Volume Dwarf Galaxies Pisces A&B: Prototypes for Local Group Dwarfs
• Identifying galaxy candidates in WSRT HI imaging of ultra-compact high velocity clouds
• A very dark stellar system lost in Virgo: kinematics and metallicity of SECCO1 with MUSE
• Detection of an Optical Counterpart to the ALFALFA Ultra-compact High Velocity Cloud AGC 249525
• Hubble Space Telescope Imaging of Isolated Local Volume Dwarfs GALFA-Dw3 and Dw4
• Catching Tidal Dwarf Galaxies at a Later Evolutionary Stage with ALFALFA
• AGC 226178 and NGVS 3543: Two deceptive dwarfs towards Virgo
• DIISC-I: The Discovery of Kinematically Anomalous HI Clouds in M 100
• Young, blue, and isolated stellar systems in the Virgo Cluster. I. 2-D Optical spectroscopy
• A Search for Gas-Rich Dwarf Galaxies in the Local Universe with ALFALFA and the WIYN One Degree Imager
• RGB Tip distance to the faint gas-rich dwarf KK 153
• Young, blue, and isolated stellar systems in the Virgo Cluster. II. A new class of stellar system