Search for intergalactic neutral hydrogen in three nearby groups of galaxies
Three nearby groups of galaxies--the M81, CVn I, and NGC 1023 groups--have been searched for 21 cm neutral hydrogen emission with the OVRO 40 m telescope. No discrete hydrogen clouds were found, so we were able to put limits on the space density of 0.25 Mpc/sup -3/ for clouds of mass > or approx. =4 x 10/sup 7/M/sub sun/, 0.15 Mpc/sup -3/ for clouds of mass 8 x 10/sup 7/M/sub sun/, and 0.02 Mpc/sup -3/ for objects of mass > or approx. =4.6 x 10/sup 8/M/sub sun/ for the three groups, respectively. These limits obtain for clouds unresolved by the beam, which subtends a linear diameter of 20 kpc at the distance of the nearest group. Generally distributed gas would have gone undetected if it were present on a scale > or approx. =700 kpc; on smaller scales any gas must have a density < or approx. =3 x 10/sup -5/ H atoms cm/sup -3/.A second survey of small selected areas in the groups with the Bonn 100 m telescope resulted in the detection of four clouds which all proved to be hitherto uncataloged, low-surface-brightness, dwarf galaxies that have properties approaching those of intergalactic H I clouds. One of these, M81 dwA, which is close to Holmberg II but probably not bound to that system, is possibly the least luminous irregular galaxy yet discovered.If we assume that our survey limits also apply to the intergalactic space in nearby groups generally, our results would have implications for several important astrophysical problems.
- Research Organization:
- Radio Astronomy Laboratory, University of California, Berkeley
- OSTI ID:
- 6291750
- Journal Information:
- Astrophys. J.; (United States), Vol. 227:3
- Country of Publication:
- United States
- Language:
- English
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