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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 | | Abstract: | We 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 | | Services: | Forum | Review | PDF | Favorites | |
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