High-resolution imaging of compact high-velocity clouds (II)

Abstract

We have imaged five compact high-velocity clouds in HI with arcmin angular- and km/s spectral-resolution using the WSRT. Supplementary total-power data, which is fully sensitive to both the cool and warm components of HI, is available for comparison for all the sources, albeit with angular resolutions that vary from 3' to 36'. The fractional HI flux in compact CNM components varies from 4% to 16% in our sample. All objects have at least one local peak in the CNM column which exceeds about 10^19 cm^-2 when observed with arcmin resolution. It is plausible that a peak column density of 1-2x10^19 cm^-2 is a prerequisite for the long-term survival of these sources. One object in our sample, CHVC120-20-443 (Davies' cloud), lies in close projected proximity to the disk of M31. This object is characterized by exceptionally broad linewidths in its CNM concentrations (more than 5 times greater than the median value). These CNM concentrations lie in an arc on the edge of the source facing the M31 disk, while the diffuse HI component of this source has a position offset in the direction of the disk. All of these attributes suggest that CHVC120-20-443 is in a different evolutionary state than most of the other CHVCs which have been studied. Similarly broad CNM linewidths have only been detected in one other object, CHVC111-07-466, which also lies in the Local Group barycenter direction and has the most extreme radial velocity known. A distinct possibility for Davies' cloud seems to be physical interaction of some type with M31. The most likely form of this interaction might be the ram-pressure or tidal- stripping by either one of M31's visible dwarf companions, M32 or NGC205, or else by a dark companion with an associated HI condensation.

12 pages, 11 (low res.) png figs, accepted for pub. in A&A

Cited by in corpus (30)

• On the Continuing Formation of the Andromeda Galaxy: Detection of HI Clouds in the M31 Halo
• A Wide-field High Resolution HI Mosaic of Messier 31: I. Opaque Atomic Gas and Star Formation Rate Density
• The WSRT wide-field HI survey: II. Local Group features
• Atomic Hydrogen Gas in Dark-Matter Minihalos and the Compact High Velocity Clouds
• Star Formation and the ISM in Four Dwarf Irregular Galaxies
• Westerbork HI observations of high-velocity clouds near M31 and M33
• First results from the Arecibo Galactic HI Survey: the disk/halo interface region in the outer Galaxy
• The many streams of the Magellanic Stream
• An HI survey of six Local Group analogs: I. Survey description and the search for high-velocity clouds
• Where are the High Velocity Clouds in Local Group Analogs?
• Relics of structure formation: extra-planar gas and high-velocity clouds around the Andromeda Galaxy
• High Velocity Cloud Complex H: A Satellite of the Milky Way in a Retrograde Orbit?
• Effelsberg HI observations of compact high-velocity clouds
• Dynamical and chemical evolution of NGC1569
• The high-velocity clouds and the Magellanic Clouds
• Gas Accretion onto the Milky Way
• The Milky Way halo as a QSO absorption-line system. New results from an HST/STIS absorption-line catalogue of Galactic high-velocity clouds
• HI Observations of the Asymptotic Giant Branch Star X Herculis: Discovery of an Extended Circumstellar Wake Superposed on a Compact High-Velocity Cloud
• The effect of clouds in a galactic wind on the evolution of gas-rich dwarf galaxies
• HI Observations of an Ultra-Compact High-Velocity Cloud
• AGC198606: A gas-bearing dark matter minihalo?
• A Search for Stellar Populations in High Velocity Clouds
• Atomic hydrogen in AGB circumstellar environments. A case study: X Her
• Identifying galaxy candidates in WSRT HI imaging of ultra-compact high velocity clouds
• Is GBT 1355+5439 a dark galaxy?
• Large and small-scale structure of the Intermediate and High Velocity Clouds towards the LMC and SMC
• Global properties of the HI high velocity sky, a statistical investigation based on the LAB survey
• A Spitzer-MIPS search for dust in compact high-velocity HI clouds
• CO and HI observations of an enigmatic cloud
• The effect of clouds on the dynamical and chemical evolution of gas-rich dwarf galaxies