A deep Hα survey of the Milky Way VI. The l = 332° area

Abstract

The Galactic plane has been observed between l = 330° to l = 336° as part of a velocity resolved Hα survey of the southern Milky Way using a scaning Fabry-Perot on a 36 cm telescope. The detailed analysis of the resultant Hα profiles reveals the presence of several layers of ionized gas with different velocities over the surveyed region. We have studied in detail both the 2-D spatial and velocity structure of the HII regions RCW102, RCW104 and RCW106. Combining these Ha observations with stellar and radio data we provide estimates for the most probable distances of these different layers. The first layer at -5 km s -1 is local emission linked to the Sco-Cen association at 170 pc. The next layer, around -24 km s -1, is at 1.9 kpc and traces the near section of the Sagittarius-Carina arm. Well connected to the Sagittarius-Carina arm portions traced in the adjacent regions (l = 328° and l = 338° area), the arm, in this longitude range, clearly shows and confirms the departure from a logarithmic spiral. The Scutum-Crux arm is also traced in this area by faint and diffuse emission at -40 km s -1 which can be placed at 3.2 kpc. The layer at -52 km s -1 is the major spiral-arm feature of the studied area; its most probable stellar distance is 4.2 kpc. An important emission component is also observed at -65 km s -1 in the southern part of the surveyed area. This mainly patchy and filamentary emission we identify as the possible optical counterpart of a Supernovae remnant centered at l = 332.0°, b = -3.2°. Finally, two complexes have been determined around 12.5 kpc which places them in the far section of the Norma arm.