Dark Matter and Galaxy Formation

K.C. Freeman, PASA, 14 (1), 4.

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Contents Page: Volume 14, Number 1

Intergalactic Clouds

The intergalactic HI clouds discovered so far are associated with individual or interacting galaxies, groups and clusters. They all have roughly similar sizes and HI masses. Here are some examples:

  • The Leo group ring (Schneider 1989). Its diameter D is about 200 kpc and its HI mass Mtex2html_wrap_inline265 is tex2html_wrap_inline293 Mtex2html_wrap_inline269.
  • The Virgo cloud (Giovanelli & Haynes 1989), with D = 200 kpc and Mtex2html_wrap_inline265 = tex2html_wrap_inline299 Mtex2html_wrap_inline269.
  • The A2634 cloud (Giovanelli et al. 1995). Its linear dimensions are about tex2html_wrap_inline303 kpc, and its Mtex2html_wrap_inline265 = tex2html_wrap_inline307 Mtex2html_wrap_inline269.
  • The cloud discovered recently near the NGC 3256/3263 system by English (1994), with D = 120 kpc and Mtex2html_wrap_inline265 = tex2html_wrap_inline307 Mtex2html_wrap_inline269.
The nature and astrophysical significance of these clouds is not yet clear. At least in some cases, like the NGC 3256/3263 example, it seems likely that they come from tidal interaction of galaxies within their parent system. Intergalactic clouds like these will not be detectable with 5 minute integrations much beyond a redshift of about 7000 km tex2html_wrap_inline253.




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