The distribution of interstellar medium in the Scd galaxy NGC 6946 and in a sample of dwarf irregular galaxies

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1988

OSTI ID:5095982

Tacconi-Garman, L J

The author has compared the atomic and molecular hydrogen distributions in the spiral galaxy NGC 6946 and in 15 dwarf irregular galaxies. He made observations of the CO J = 1 {yields} 0 transition to obtain a fully sampled map to a radium of 10 kpc in NGC 6946, using the 14-meter telescope of the Five College Radio Astronomy Observatory, and also completely mapped the 21-cm line of neutral hydrogen with the Very Large Array. He has also made CO observations at FCRAO in 15 dwarf irregular galaxies spanning a wide range of infrared luminosity and color. In NGC 6946 the CO HI maps were used to investigate the radial and azimuthal variations in the atomic and molecular gas. The H{sub 2} mass is found to dominate the ISM in the inner disk of this galaxy. The H{sub 2}, H{alpha}, radio continuum, and blue light radial profiles are found to be centrally peaked with exponential falloffs, while the HI distribution is much flatter, with a central depression. He infers a constant efficiency of star formation with radium in NGC 6946 and suggest that HI plays only a passive role in the star formation process of this galaxy. Spiral arm enhancements in the H{sub 2} surface densities, H{alpha} surface brightnesses, and {sigma} (H{sub 2})/{mu}(H{alpha}) ratios are observed. The presence of these arm enhancements, as well as enhancements in the gas surface densities in interarm regions is consistent with a picture in which cloud-cloud collisions play an important role in the star formation process in NGC 6946. For the dwarf galaxies, high observed L{sub IR}/L{sub CO} ratios in the blue systems are indicative of a present burst of star formation, while the red systems exhibit low L{sub IR}/L{sub CO} ratios.

• Research Organization: Massachusetts Univ., Amherst, MA (USA)
• OSTI ID: 5095982
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics & Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ASTRONOMY
ATOMS
COLLISIONS
COMPARATIVE EVALUATIONS
CONFIGURATION
COSMIC GASES
COSMIC RADIO SOURCES
DENSITY
DISTRIBUTION
ELECTROMAGNETIC RADIATION
ELEMENTS
FLUIDS
GALAXIES
GASES
H1 REGIONS
HYDROGEN
INTERSTELLAR SPACE
MASS
MOLECULES
MORPHOLOGY
NONMETALS
PHYSICAL PROPERTIES
RADIATIONS
RADIOASTRONOMY
RADIOWAVE RADIATION
SPACE
SPATIAL DISTRIBUTION
SPIRAL CONFIGURATION
STAR EVOLUTION
VARIATIONS