An extragalactic HI cloud with no optical counterpart?

被引:49
作者
Kilborn, VA [1 ]
Staveley-Smith, L
Marquarding, M
Webster, RL
Malin, DF
Banks, GD
Bhathal, R
de Blok, WJG
Boyce, PJ
Disney, MJ
Drinkwater, MJ
Ekers, RD
Freeman, KC
Gibson, BK
Henning, PA
Jerjen, H
Knezek, PM
Koribalski, B
Minchin, RF
Mould, JR
Oosterloo, T
Price, RM
Putman, ME
Ryder, SD
Sadler, EM
Stewart, I
Stootman, F
Wright, AE
机构
[1] Univ Melbourne, Sch Phys, Parkville, Vic 3052, Australia
[2] CSIRO, Australia Telescope Natl Facil, Epping, NSW 2121, Australia
[3] Anglo Australian Observ, Epping, NSW 2121, Australia
[4] Univ Wales, Dept Phys & Astron, Cardiff CF2 3YB, S Glam, Wales
[5] Univ Western Sydney Macarthur, Dept Phys, Campbelltown, NSW 2560, Australia
[6] Australian Natl Univ, Res Sch Astron & Astrophys, Weston, ACT 2611, Australia
[7] Univ Colorado, Ctr Astrophys & Space Astron, Boulder, CO 80309 USA
[8] Univ New Mexico, Dept Phys & Astron, Albuquerque, NM 87131 USA
[9] Space Telescope Sci Inst, Baltimore, MD 21218 USA
[10] Ist Fis Cosm, I-20133 Milan, Italy
[11] Joint Astron Ctr, Hilo, HI 96720 USA
[12] Univ Sydney, Sch Phys, Dept Astrophys, Sydney, NSW 2006, Australia
关键词
galaxies : formation; galaxies : irregular; radio emission lines;
D O I
10.1086/301542
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
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 x 10(7) M-circle dot, using an estimated distance of similar to 3.2 Mpc. Most significantly, we have found no optical companion to this object to very faint limits [mu(B) similar to 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 x 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 similar to 2 x 10(8) yr ago.
引用
收藏
页码:1342 / 1350
页数:9
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