Extended H I regions around spiral galaxies: a probe for galactic structure and the intergalactic medium

Journal Article · Tue Nov 01 04:00:00 EST 1977 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/155635· OSTI ID:5280980

Bergeron, J

The H I disks observed at large radii around nearby spiral galaxies provide sensitive probes for the mass distributions in these galaxies and of their environments. We show, for a few well-observed systems, that there is an unseen component which dominates the mass at large radii. This additional matter cannot be gas, either neutral or ionized. The data do not distinguish strongly between flat and spherical spatial distributions for this mass, though they suggest that the distribution is spherical. An observational test is proposed to differentiate the two. We investigate the thermal interaction between a hot intergalactic medium near the closure density and these extended H I regions in the assumption of magnetic field lines extended outward into the intergalactic medium (IGM). We show that, with plausible initial conditions, the intergalactic temperature at present cannot exceed 1 x 10/sup 7/ K if the H I is to have survived until now. Consideration of conditions in the past places even more stringent limits on the temperature and density of the IGM. Survival of the H I disk also implies that these galaxies cannot have persistent hot, dense halos. The X-ray observations of M31, in particular, cannot be interpreted in terms of a thermal bremsstrahlung halo model, unless this halo is younger than about 10/sup 7/ yr.

• Research Organization: W. K. Kellogg Radiation Laboratory, California Institute of Technology, Carnegie Institution of Washington
• OSTI ID: 5280980
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 217:3; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics & Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COSMIC GASES
COSMIC RADIATION
COSMIC RADIO SOURCES
ELECTROMAGNETIC RADIATION
EVAPORATION
FLUIDS
GALAXIES
GASES
H1 REGIONS
H2 REGIONS
INTERGALACTIC SPACE
IONIZATION
IONIZING RADIATIONS
MAGNETIC FIELDS
PHASE TRANSFORMATIONS
RADIATIONS
SPACE
X RADIATION