Galactic density wave, molecular clouds, and star formation

Journal Article · Sat Oct 15 04:00:00 EDT 1977 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/155595· OSTI ID:5351757

Bash, F N; Green, E; Peters, III, W L

A dynamical model has been devised for the galactic orbits of molecular clouds after their birth in the galactic density wave. This model suggests a picture in which young protoclusters or associations and their associated placental interstellar material actively radiate /sup 12/C/sup 16/O spectral line radiation at 115 GHz until about 30 million years after birth, at which time there is an abrupt cutoff of that spectral line radiation.A survey of 63 young open clusters reveals associated 115 GHz emission if the cluster or association contains main-sequence O stars, but the associated emission is not present for clusters whose earliest main-sequence star is B0 or later, confirming the cutoff predicted by the dynamical model.This association between /sup 1/2C/sup 16/O spectral line radiation and open clusters containing young stars has allowed us to use the surface density of /sup 12/C/sup 16/O to determine the surface density of young clusters, and we have used the dynamical model to determine their corresponding birth locations and birthrates. We also derive the birthrate of open clusters averaged over the Galaxy.In addition, it has been suggested that if supernovae in the cluster are capable of ridding the cluster of its interstellar gas, thereby stopping the CO spectral line radiation, then these observations give an upper mass limit for stars that become supernovae.Next we discuss recombination line observations of H II regions and compare the predictions of our dynamical model for them against the predictions for CO molecular clouds.Finally we compare our independent time scale from the dynamical model with conventional stellar evolution time scales. They agree if about 20 million years elapse between the time and interstellar cloud passes through the spiral-shock wave and the time when stars begin to form in the cloud.

• Research Organization: Department of Astronomy, The University of Texas at Austin
• OSTI ID: 5351757
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 217:2; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640102 -- Astrophysics & Cosmology-- Stars & Quasi-Stellar
Radio & X-Ray Sources
640105* -- Astrophysics & Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CHALCOGENIDES
COSMIC DUST
COSMIC GASES
COSMIC RADIO SOURCES
DISTRIBUTION
DUSTS
FLUIDS
GALAXIES
GASES
H2 REGIONS
INTERSTELLAR SPACE
MILKY WAY
OXIDES
OXYGEN COMPOUNDS
SPACE
SPATIAL DISTRIBUTION
STAR ACCRETION
STAR CLUSTERS
STAR EVOLUTION
STARS
SUPERNOVAE