High-resolution maps of 6 centimeter formaldehyde: clumping in molecular clouds

Journal Article · Sun Dec 01 04:00:00 EST 1985 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/163708· OSTI ID:6103028

Martin-Pintado, J; Wilson, T L; Johnston, K J; Henkel, C

VLA maps of W31, W33, W49, and W51 in the 1/sub 10/--1/sub 11/ line of ortho-H/sub 2/CO are presented. The maps were made with angular resolutions of 10''--15'' and a velocity resolution of 1.8 km s/sup -1/. The total velocity coverage was 45 km s/sup -1/. In all of the regions measured, the ortho-H/sub 2/CO distribution breaks up into a number of condensations, or clumps. For W33 and W49, all of the single-dish line flux density is present in our VLA maps; for the other two, about 70% is measured. Averaged over all of the sources, the median clump size is 0.5 pc with a range from <0.2 pc (one-half of the beam size) to >1.4 pc. The median apparent optical depth is 0.4 with a range from <0.1 to 1.1. The median line width (FWHP) is 5.0 km s/sup -1/, with a range from <1 km s/sup -1/ to 12 km s/sup -1/. The median space densities of ortho-H/sub 2/CO are calculated on a source-by-source basis. Combining these with H/sub 2/ densities, we find that the (ortho-H/sub 2/CO/H/sub 2/) ratios are about an order of magnitude larger than the prediction of Wootten and colleagues published in 1978. Based on line width, the clumps can be placed in two categories: those having FWHP widths < or =1 km s/sup -1/ and those having widths larger than 3 km s/sup -1/. The first group could follow the relation given by Larson in 1981 and might have masses which agree with virial estimates. For the second group, comparisons of our data with the analysis of Larson show that (1) our clumps have approx.10% of the sizes predicted from the line widths, and (2) the masses of most of these clumps toward W31 and W51 are 20%--60% of the virial mass estimates.

• Research Organization: Max-Planck-Institut fuer Radioastronomie, Bonn, FRG
• OSTI ID: 6103028
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 299:1; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics &amp; Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABSORPTION SPECTRA
ALDEHYDES
CHEMICAL COMPOSITION
COSMIC RADIO SOURCES
DISTRIBUTION
FORMALDEHYDE
H2 REGIONS
INTERFEROMETRY
INTERSTELLAR GRAINS
LINE WIDTHS
MAPS
OPACITY
OPTICAL PROPERTIES
ORGANIC COMPOUNDS
PARTICLES
PHYSICAL PROPERTIES
RADIAL VELOCITY
SPATIAL DISTRIBUTION
SPECTRA
VELOCITY