Searching for converging flows of atomic gas onto a molecular cloud

Abstract

We present new observations of [CII] fine structure line emission from an isolated molecular cloud using the upGREAT instrument onboard SOFIA. These data are analyzed together with archival CO=1-0 and HI 21 cm emission spectra to investigate the role of converging atomic gas flows in the formation of molecular clouds. Bright [CII] emission is detected throughout the mapped area that likely originates from photodissociation regions excited by UV radiation fields produced by newborn stars within the cloud. Upon spatial averaging of the [CII] spectra, we identify weak [CII] emission within velocity intervals where the HI 21 cm line is brightest; these are blue-shifted relative to velocities of the CO and bright [CII] emission by 4 km/s. The brightness temperatures, velocity dispersions, and alignment with HI 21 cm velocities connect this [CII] emission component to the cold, neutral atomic gas of the interstellar medium (CNM). We propose that this CNM feature is an accretion flow onto the far--side of the existing molecular cloud. The mass infall rate is 3.2x10**{-4} Msun/yr. There is no direct evidence of a comparable red--shifted component in the [CII] or HI 21 cm spectral lines that would indicate the presence of a converging flow.

11 pages, 7 figures, accepted by ApJ

References in corpus (6)

• Theory of Star Formation
• The SCUBA Legacy Catalogue: Continuum Objects Detected by SCUBA
• The Birth of Molecular Clouds: Formation of Atomic Precursors in Colliding Flows
• GREAT/SOFIA atmospheric calibration
• The upGREAT 1.9 THz multi-pixel high resolution spectrometer for the SOFIA Observatory
• Fragmentation and kinematics in high-mass star formation: CORE-extension targeting two very young high-mass star-forming regions

Cited by in corpus (1)

• Research on the Interstellar Medium and Star Formation in the Galaxy: An Indian Perspective