Supergalactic studies. II - Supergalactic distribution of the nearest intergalactic gas clouds

Journal Article · Mon Dec 01 04:00:00 EST 1975 · Astrophysical Journal

DOI:https://doi.org/10.1086/153980· OSTI ID:4057128

de Vaucouleurs, G.; Corwin, H. G. ,. Jr.

The report by Mathewson, Cleary, and Murray that the nearby ''high velocity'' H i clouds, and in particular the Magellanic Stream, are strongly concentrated toward the supergalactic plane is confirmed. The observed concentration within +-30degree from the supergalactic equator of 21 out of 25 clouds in the north galactic hemisphere and 27 out of 31 clouds in the south galactic hemisphere could occur by chance in less than 7 and 3 percent of random samples from a population having a statistically isotropic Poisson distribution. Since the two galactic hemispheres are substantially independent samples, the combined probability of the chance hypothesis is P<2x10^-3. It is found that actually the high-velocity clouds are not so much concentrated toward the supergalactic equator (SGE) as toward the equator of the ''Local Cloud'' of galaxies inclined 14degree to the main supergalactic plane. Both galaxies and H i clouds define the same small circle of maximum concentration and exhibit the same standard deviation (15degree) from it, demonstrating closely related space distributions. It is concluded that, with the possible exception of a few of the largest and probably nearest cloud complexes (MS, AC, C), most of the high- velocity clouds are truly intergalactic and associated with the Local Group and nearer groups of galaxies. Half the population in a total sample of 115 nearby galaxies and intergalactic gas coulds is within 11degree from the Local equator, indicating a half-thickness of approx.0.75 Mpc for the Local Cloud. Intergalactic gas clouds have already been identified near 10 of the nearest galaxies (including our Galaxy and the Magellanic Clouds), most within approx.3 Mpc. The estimated space density of intergalactic gas clouds is Napprox. =20-- 25 Mpc^-3, in approximate agreement with the densities required by the collision theory of ring galaxies.

• Research Organization: Department of Astronomy and McDonald Observatory, University of Texas at Austin
• Sponsoring Organization: USDOE
• NSA Number: NSA-33-024102
• OSTI ID: 4057128
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Vol. 202; ISSN 0004-637X
• Publisher: Institute of Physics (IOP)
• Country of Publication: United States
• Language: English

Related Subjects

*COSMIC GASES-- SPATIAL DISTRIBUTION
*INTERGALACTIC SPACE-- COSMIC GASES
79 ASTRONOMY AND ASTROPHYSICS
GALAXY CLUSTERS
ISOTROPY
MAGELLANIC CLOUDS
NEBULAE
VELOCITY