Multi‐ionic Kinematical Study of the HiiRegion Sharpless 2‐158

Abstract

The Sh 2-158 gas complex kinematics is analyzed using four lines from three different ions (Hα, [O III] λ5007, and [S II] λλ6727, 6731) and the CO 1-0 line. The O++ and S+ data cubes were obtained using MOS FP at the CFHT, while the H+ data cube was obtained using FaNTOmM at the Observatoire du mont Megantic. More than 200,000 spectra (S/N ≥ 5) were obtained. Maps of the radial velocity fields, the velocity line width field, and the electronic density field are discussed. All ionic mean radial velocities are blueshifted with respect to the molecular cloud (VLSR = -55.16 ± 0.02 km s-1), more so as one goes from [S II] to Hα to [O III]. Two flows originating from the molecular cloud are identified. The encounter of the two flows, and possibly stellar winds, induces turbulence near the stars, causing larger line widths (≈10 km s-1) than elsewhere in the field. The mean [S II] line width is smaller than the mean [O III] line width, which is smaller than the mean Hα line width. Those differences between the ions are explained by the smaller [O III] Stromgren sphere compared to the Hα Stromgren sphere and the restriction of [S II] to a shell of gas near the molecular cloud. The most probable density value is 225 ± 25 cm-3. The observations are mostly in agreement with the Champagne model. A geometrical model is proposed for Sh 2-158.