Identifying galaxy candidates in WSRT HI imaging of ultra-compact high velocity clouds

Abstract

Ultra-compact high velocity clouds (UCHVCs) were identified in the ALFALFA HI survey as potential gas-bearing dark matter halos. Here we present higher resolution neutral hydrogen (HI) observations of twelve UCHVCS with the Westerbork Synthesis Radio Telescope (WSRT). The UCHVCs were selected based on a combination of size, isolation, large recessional velocity and high column density as the best candidate dark matter halos. The WSRT data were tapered to image the UCHVCs at 210" (comparable to Arecibo) and 105" angular resolution. In a comparison of the single-dish to interferometer data, we find that the line flux recovered in the WSRT observations is comparable to that from the single-dish ALFALFA data. In addition, any structure seen in the ALFALFA data is reproduced in the WSRT maps at the same angular resolution. At 210'" resolution all the sources are generally compact with a smooth HI morphology, as expected from their identification as UCHVCs. At the higher angular resolution, a majority of the sources break into small clumps contained in a diffuse envelope. These UCHVCs also have no ordered velocity motion and are most likely Galactic halo clouds. We identify two UCHVCs, AGC 198606 and AGC 249525, as excellent galaxy candidates based on maintaining a smooth HI morphology at higher angular resolution and showing ordered velocity motion consistent with rotation. A third source, AGC 249565, lies between these two populations in properties and is a possible galaxy candidate. If interpreted as gas-bearing dark matter halos, the three candidate galaxies have rotation velocities of 8-15 km/s, HI masses of 0.6-50 x 10^5 Msun, HI radii of 0.3-2 kpc, and dynamical masses of 2-20 x 10^7 Msun for a range of plausible distances. These are the UCHVCs with the highest column density values in the ALFALFA HI data and we suggest this is the best way to identify further candidates.

Accepted for publication in A&A. 26 pages, 19 figures, 5 tables

References in corpus (17)

• Properties of galaxies reproduced by a hydrodynamic simulation
• High-Resolution Rotation Curves and Galaxy Mass Models from THINGS
• Is there a "too big to fail" problem in the field?
• Bent by baryons: the low mass galaxy-halo relation
• The Arecibo Legacy Fast ALFA Survey: III. HI Source Catalog of the Northern Virgo Cluster Region
• The Dearth of Neutral Hydrogen in Galactic Dwarf Spheroidal Galaxies
• The Local Group dwarf Leo T: HI on the brink of star formation
• A spectroscopic confirmation of the Bootes II dwarf spheroidal
• Variable stars in the newly discovered Milky Way satellite in Bootes
• A Catalog of Ultra-compact High Velocity Clouds from the ALFALFA Survey: Local Group Galaxy Candidates?
• The effect of feedback and reionization on star formation in low-mass dwarf galaxy haloes
• ALFALFA Discovery of the Nearby Gas-rich Dwarf Galaxy Leo P. V. Neutral Gas Dynamics and Kinematics
• A Comprehensive Archival Search for Counterparts to Ultra-Compact High Velocity Clouds: Five Local Volume Dwarf Galaxies
• SHIELD: Neutral Gas Kinematics and Dynamics
• SHIELD: Comparing Gas and Star Formation in Low Mass Galaxies
• The StEllar Counterparts of COmpact high velocity clouds (SECCO) survey. I. Photos of ghosts
• AGC198606: A gas-bearing dark matter minihalo?

Cited by in corpus (6)

• The FAST all sky HI survey (FASHI): The first release of catalog
• The Enigmatic (Almost) Dark Galaxy Coma P: The Atomic Interstellar Medium
• Detection of an Optical Counterpart to the ALFALFA Ultra-compact High Velocity Cloud AGC 249525
• AGC 226178 and NGVS 3543: Two deceptive dwarfs towards Virgo
• A Search for Gas-Rich Dwarf Galaxies in the Local Universe with ALFALFA and the WIYN One Degree Imager
• Young, blue, and isolated stellar systems in the Virgo Cluster. II. A new class of stellar system