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22 January 2022
 
  » arxiv » astro-ph/0005267

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An Extragalactic HI Cloud with No Optical Counterpart?
V. A. Kilborn ; L. Staveley-Smith ; M. Marquarding ; R. L. Webster ; D. F. Malin ; G. D. Banks ; R. Bhathal ; W. J. G. de Blok ; P. J. Boyce ; M. J. Disney ; M. J. Drinkwater ; R. D. Ekers ; K. C. Freeman ; B. K. Gibson ; P. A. Henning ; H. Jerjen ; P. M. Knezek ; B. Koribalski ; R. F. Minchin ; J. R. Mould ; T. Oosterloo ; R. M. Price ; M. E. Putman ; S. D. Ryder ; E. M. Sadler ; I. Stewart ; F. Stootman ; A. E. Wright ;
Date 12 May 2000
Subject astro-ph
AbstractWe report the discovery, from the HI Parkes All-Sky Survey (HIPASS), of an isolated cloud of neutral hydrogen which we believe to be extragalactic. The HI mass of the cloud (HIPASS J1712-64) is very low, 1.7 x 10^7 Msun, using an estimated distance of ~3.2 Mpc. Most significantly, we have found no optical companion to this object to very faint limits (mu(B)~ 27 mag arcsec^-2). HIPASS J1712-64 appears to be a binary system similar to, but much less massive than, HI 1225+01 (the Virgo HI Cloud) and has a size of at least 15 kpc. The mean velocity dispersion, measured with the Australia Telescope Compact Array (ATCA), is only 4 km/s for the main component and because of the weak or non-existent star-formation, possibly reflects the thermal linewidth (T<2000 K) rather than bulk motion or turbulence. The peak column density for HIPASS J1712-64, from the combined Parkes and ATCA data, is only 3.5 x 10^19 cm^-2, which is estimated to be a factor of two below the critical threshold for star formation. Apart from its significantly higher velocity, the properties of HIPASS J1712-64 are similar to the recently recognised class of Compact High Velocity Clouds. We therefore consider the evidence for a Local Group or Galactic origin, although a more plausible alternative is that HIPASS J1712-64 was ejected from the interacting Magellanic Cloud/Galaxy system at perigalacticon ~ 2 x 10^8 yr ago.
Source arXiv, astro-ph/0005267
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