Please use this identifier to cite or link to this item: http://hdl.handle.net/1959.3/210876

Title

An extragalactic H I cloud with no optical counterpart?

Author(s)

Kilborn, V. A.;  Staveley-Smith, L.;  Marquarding, M.;  Webster, R. L.;  Malin, D. F.;  Banks, G. D.;  Bhathal, R.;  De Blok, W. J. G.;  Boyce, P. J.;  Disney, M. J.;  Drinkwater, M. J.;  Ekers, R. D.;  Freeman, K. C.;  Gibson, B. K.;  Henning, P. A.;  Jerjen, H.;  Knezek, P. M.;  Koribalski, B.;  Minchin, R. F.;  Mould, J. R.;  Oosterloo, T.;  Price, R. M.;  Putman, M. E.;  Ryder, S. D.;  Sadler, E. M.;  Stewart, I.;  Stootman, F.;  Wright, A. E.

Abstract

We report the discovery, from the H I Parkes All-Sky Survey (HIPASS), of an isolated cloud of neutral hydrogen, which we believe to be extragalactic. The H I mass of the cloud (HIPASS J1712-64) is very low, 1.7 × 107 Modot, using an estimated distance of ~3.2 Mpc. Most significantly, we have found no optical companion to this object to very faint limits [μ(B) ~ 27 mag arcsec-2]. HIPASS J1712-64 appears to be a binary system similar to, but much less massive than, H I 1225+01 (the Virgo H I 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-1 for the main component and, because of the weak or nonexistent star formation, possibly reflects the thermal line width (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 × 1019 cm-2, which is estimated to be a factor of 2 below the critical threshold for star formation. Apart from its significantly higher velocity, the properties of HIPASS J1712-64 are similar to the recently recognized 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 × 108 yr ago.

Publication type

Journal article

Source

The Astronomical Journal, Vol. 120, no. 3 (Sep 2000), pp. 1342-1350

Publication year

2000

FOR Code(s)

0201 Astronomical and Space Sciences

Keyword(s)

Galaxies: formation;  Galaxies: irregular;  Radio emission lines

Publisher

University of Chicago Press

ISSN

0004-6256

Publisher URL

http://dx.doi.org/10.1086/301542

Copyright

Copyright © 2000 The American Astronomical Society. All rights reserved. The American Astronomical Society does not allow institutions to archive either the accepted manuscript or the published version of the article. However, you can find an earlier version of the full text here: http://arxiv.org/abs/astro-ph/0005267.

Peer reviewed