W43: the closest molecular complex of the Galactic Bar?
Abstract
We used a large database extracted from Galaxy-wide surveys of H I, 13CO 1-0, 8 and 870 continuum to trace diffuse atomic gas, low- to medium-density molecular gas, high-density molecular gas, and star formation activity which we complemented by dedicated 12CO 2--1, 3--2 observations of the W43 region. From the detailed 3D (space-space-velocity) analysis of the molecular and atomic cloud tracers through the region and despite its wide velocity range (FWHM22.3 around 95.9 ), we identified W43 as a large (equivalent diameter 140 pc) and coherent complex of molecular clouds which is surrounded by an atomic gas envelope (equivalent diameter 290 pc). We measured the total mass of this newly-identified molecular complex (M total 7.1 × 106 ), the mass contained in dense 870 clumps (<5 pc dense cloud structures, M clumps 8.4 × 105 ) and conclude that W43 is particularly massive and concentrated. The distance we assume for the W43 complex is 6 kpc from the Sun, which may place it at the meeting point of the Scutum-Centaurus (or Scutum-Crux) Galactic arm and the Bar, a dynamically complex region where high-velocity streams could easily collide. The star formation rate of W43 is suggested not to be steady but it is increasing from \, 0.01 \, yr-1 (measured from its 8\,μm luminosity) to 0.1 \, yr-1 (measured from its molecular content). From the global properties of W43, we claim it is an extreme molecular complex in the Milky Way and it could even be forming starburst clusters in the near future.