Extremely High Velocity Outflows

Extremely high velocity (EHV) wings, with full widths of 72 to 140 km s, are seen on the CO J = 3→2 lines toward W3 IRS 5, GL 490, NGC 2071, W28 A2 (G05.89–0.39), GL 2591, S140, and Cepheus A. Observations of CO and CO J = 3→2 and J = 2→1 lines indicate that optical depth generally decreases with increasing velocity separation from the ambient cloud velocity. Maps of the extremely high velocity (|V −V0| >∼ 20 km s ) and the high-velocity (5 <∼ |V − V0| <∼ 20 km s ) CO emission components show that the morphology of the two components is similar in W3 IRS 5 and W28 A2 but may be different in GL 2591, S140, and Cepheus A. The results of our survey suggest that EHV wings are common around infrared sources of moderate to high luminosity [500 to (4 × 10) L⊙] in dense regions. Line ratios imply that the EHV gas is usually optically thin and warm. Characteristic velocities range from 20 to 40 km s, yielding timescales of 1600–4200 yr. Since most sources in this study are producing some ionizing photons, these short timescales suggest that neutral winds coexist with ionizing photons. We examined two possible sources for the extremely high velocity CO emission: a neutral stellar wind; and swept-up or entrained molecular gas. Neither can be ruled out. If the high-velocity (HV) gas is swept up by a momentum-conserving stellar wind traced by the extremely high velocity CO emission, most of the C in the winds from luminous objects cannot be in CO. If the EHV and HV forces are equal, the fraction of C in a form other than CO increases with source luminosity and with the production rate of ionizing photons. This trend is natural in the stellar wind hypothesis, but models of winds around such luminous objects are needed. We consider other possible chemical states for the carbon in the stellar wind. Subject headings: ISM: jets and outflows — ISM: kinematics and dynamics — ISM: molecules Electronic mail: [email protected] Electronic mail: [email protected] Electronic mail: [email protected]