W49A North: Global or Local or No Collapse?

Abstract

We attempt to fit observations with 500 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 2000 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 toward 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 500 beam) toward H II region G arises from different components in the three 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 1-5 km s(-1) for a turbulent velocity of about 6 km s(-1). High-resolution observations of the J = 1-0 and 5-4 transitions of CS and (CS)-S-34 may distinguish between these three models. Modeling existing observations of HCO+ and (CO)-O-18 does not allow one to distinguish between the three models but does indicate the existence of a bipolar outflow.