Abstract
We present Very Large Array (VLA) continuum (2, 3.6, and 20 cm) and line (H I 21 cm, C92α, and H92α) observations toward the obscured cometary-like H II region located near the optical nebulosities GGD 12-15. We find that the H92α recombination line profile 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 flow. The C92α observations show that the C+ emission arises from an extended region of ~20'' 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 (~11 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 ~23'' 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 (≤22''), has a line center velocity of 11.7 km s-1, and lies in front of the H II region. Both the C92α 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 ~330 K, a hydrogen column density of ~6 × 1021 cm-2, a H I number density of ~1.5 × 104 cm-3, and a H I mass of ~5 M☉. The mass in photodissociated hydrogen is about 3 orders of magnitude larger than the mass in ionized hydrogen (~2 × 10-3 M☉).
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