Aperture Synthesis CS Observations of NGC 7538 IRS 1—3: Ring of Dense Gas around IRS 1
Ryohei Kawabe, Mika Suzuki, Naomi Hirano, Kenji Akabane, Mary Barsony, Joan R. R, Osamu Kameya, Masato IshiguroAbstract
We have carried out aperture synthesis CS (J = 2—1) observations of the dense molecular gas around a young stellar object NGC 7538 IRS 1–3 with 6″ resolution using the Nobeyama Millimeter Array (NMA). We have found that the dense molecular gas has a ring-like structure centered on an infrared source NGC 7538 IRS 1. The ring has a diameter of 20″ (0.26 pc) and an H2 mass of 230M◉. The velocity structure of CS (2—1) emission indicates the existence of an expanding motion of the ring (Vexp ~ 1 km s-1/sini, where i is the inclination angle of the ring). These results suggest that the observed structure is a nearly face-on view of a protostellar disk of molecular gas with a central hole formed by wind from IRS 1. IRS 2 and IRS 3 are apparently on the ring. In addition to the structure, several clumps of dense gas have been found around the ring. These clumps have a typical size of 10″ (0.13 pc) and a velocity dispersion of 1–2 km s-1; the H2 masses range from 20 to 60M◉. It is suggested that these clumps are gravitationally bound, and would be protostellar condensations.