Active Star Formation toward the Ultracompact HiiRegions G45.12+0.13 and G45.07+0.13

Abstract

A multiwavelength study of the molecular cores containing the ultracompact (UC) H II regions G45.12+0.13 and G45.07+0.13 reveals a series of phenomenological differences that distinguish the age of these cores in terms of their development of high-mass star formation. First, we report the discovery of massive, bipolar molecular outflows from both UC H II regions. The G45.12+0.13 UC H II region lies centered on a spatially extended, 6 km s-1 outflow that we have mapped in the CO J = 2 ? 1, 3 ? 2, 6 ? 5,13CO 2 ? 1, and C18O 2 ? 1 transitions at the Caltech Submillimeter Observatory (CSO). The broad bipolar structure is optically thick in the 12CO line. The 13CO measurements imply a large outflow mass of 4800 M? (12% of the total cloud mass). Interferometric observations with the Owens Valley Radio Observatory (OVRO) millimeter array in the 13CO 1 ? 0 line resolve the gas into at least two outflows, one of which emanates from the 4.0 Jy, 110 GHz source identified with the UC H II region. An additional outflow is driven by an adjacent young, embedded object that contributes to the extended submillimeter continuum emission imaged with the CSO bolometer array camera. Lying in a separate core a few arcminutes away, the G45.07+0.13 UC H II region contains H2O masers and presents higher velocity (11 km s-1) yet more compact CO emission. An outflow has been detected in the CO 6 ? 5 transition, along with a compact submillimeter continuum source. OVRO observations in the CS J = 2 ? 1 transition confirm a compact outflow centered on the 98 GHz continuum source toward which infall is also seen in the form of redshifted absorption. The multiple outflows, higher CO antenna temperatures, more extended submillimeter and radio continuum emission, and lack of H2O masers all distinguish the core containing G45.12+0.13 as a more advanced site of massive star formation than the neighboring core containing G45.07+0.13.