A photodissociated region associated with the compact Hıı region near GGD 12-15

Artículo de publicación ISIWe present Very Large Array (VLA) continuum (2, 3.6, and 20 cm) and line (H I 21 cm, C92a, and H92a) observations toward the obscured cometary-like H II region located near the optical nebulosities GGD 12È15. We Ðnd that the H92a recombination line proÐle is asymmetric, probably due to a superposition of line emission from the H II region and from an underlying partially ionized medium (H0). The observed kinematics of the ionized gas suggests that the H II region is undergoing a champagne Ñow. The C92a observations show that the C` emission arises from an extended region of D20A in size that is closely associated with the H II region. The C` emission has a line center velocity of 11.9 km s~1, similar to the velocity of the ambient molecular cloud (D11 km s~1). The 21 cm H I spectrum shows emission and absorption line components. The H I line in emission is detected from a region of D23A in diameter, with a center velocity of 15.4 km s~1 and peaks to the east of the H II region. The absorption feature is unresolved (¹22A), has a line center velocity of 11.7 km s~1, and lies in front of the H II region. Both the C92a and H I emissions are interpreted as arising from a photodissociated region (PDR) around the cometary H II region. An isothermal model has been used to derive the physical parameters of the photodissociated hydrogen gas around the H II region. We derive that the PDR region has an excitation temperature of D330 K, a hydrogen column density of D6]1021 cm~2, a H I number density of D1.5]104 cm~3, and a H I mass of D5 M The mass in photodissociated hydro- _. gen is about 3 orders of magnitude larger than the mass in ionized hydrogen (D2]10~3 M_). Subject headings : H II regions È ISM: abundances È ISM: individual (GGD 12È15) ÈWe thank the referee Gianni Tofani for useful comments that helped improved the presentation of the paper. M. L., L. F. R., S. L., V. E., J. C., and Y. G. acknowledge Ðnancial support from DGAPA-UNAM 102395, IN101695, and CONACyT-Mexico 4616-E9406. Y. G. also acknowledges partial Ðnancial support from the Third World Academy of Sciences and the ACAL UNESCO Fellowship. G. G. acknowledges support from a Chilean Presidential Science Fellowship and FONDECYT project 1950524