Astronomy and Astrophysics – Astrophysics
Scientific paper
2004-05-05
Astronomy and Astrophysics
Astrophysics
42 pages, 27 figures, accepted for publication in the ApJS August 2004, v153 issue
Scientific paper
10.1086/422173
We attempt to fit observations with 5" resolution of the J=2-1 transition of CS in the directions of H II regions A, B, and G of W49A North as well as observations with 20" resolution of the J=2-1, 3-2, 5-4, and 7-6 transitions in the directions of H II regions A and G by using radiative transfer calculations. These calculations predict the intensity profiles resulting from several spherical clouds along the line of sight. We consider three models: global collapse of a very large (5 pc radius) cloud, localized collapse from smaller (1 pc) clouds around individual H II regions, and multiple, static clouds. For all three models we can find combinations of parameters that reproduce the CS profiles reasonably well provided that the component clouds have a core-envelope structure with a temperature gradient. Cores with high temperature and high molecular hydrogen density are needed to match the higher transitions (e.g. J=7-6) observed towards A and G. The lower temperature, low density gas needed to create the inverse P-Cygni profile seen in the CS J=2-1 line (with 5" beam) towards H II region G arises from different components in the 3 models. The infalling envelope of cloud G plus cloud B creates the absorption in global collapse, cloud B is responsible in local collapse, and a separate cloud, G', is needed in the case of many static clouds. The exact nature of the velocity field in the envelopes for the case of local collapse is not important as long as it is in the range of 1 to 5 km/s for a turbulent velocity of about 6 km/s. High resolution observations of the J=1-0 and 5-4 transitions of CS and C34S may distinguish between these three models. Modeling existing observations of HCO+ and C18O does not allow one to distinguish between the three models but does indicate the existence of a bipolar outflow.
Auer Lawrence H.
Dickel Helene R.
Williams John A.
No associations
LandOfFree
W49A North - Global or Local or No Collapse? does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with W49A North - Global or Local or No Collapse?, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and W49A North - Global or Local or No Collapse? will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-466830