The onset of high-mass star formation in the direct vicinity of the Galactic mini-starburst W43^⋆

¹ Max-Planck-Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: name@mpia.de
² Max Planck Institute for Radioastronomy, Auf dem Hügel 69, 53121 Bonn, Germany
³ University of Cologne, Zülpicher Strasse 77, 50937 Köln, Germany
⁴ Laboratoire AIM Paris-Saclay, CEA/IRFU, CNRS/INSU, Université Paris Diderot, Service d’Astrophysique, CEA-Saclay, Bât. 709, 91191 Gif-sur-Yvette Cedex, France
⁵ Institute of Astronomy, The University of Tokyo, Osawa, Mitaka, 181-0015 Tokyo, Japan

Received: 8 August 2011
Accepted: 22 November 2011

Abstract

Context. The earliest stages of high-mass star formation are still poorly characterized. Densities, temperatures and kinematics are crucial parameters for simulations of high-mass star formation. It is also unknown whether the initial conditions vary with environment.

Aims. We want to investigate the youngest massive gas clumps in the environment of extremely active star formation.

Methods. We selected the IRDC 18454 complex, directly associated with the W43 Galactic mini-starburst, and observed it in the continuum emission between 70 μm and 1.2 mm with Herschel, APEX and the 30 m telescope, and in spectral line emission of N₂H⁺ and ¹³CO with the Nobeyama 45 m, the IRAM 30 m and the Plateau de Bute Interferometer.

Results. The multi-wavelength continuum study allows us to identify clumps that are infrared dark even at 70 μm and hence the best candidates to be genuine high-mass starless gas clumps. The spectral energy distributions reveal elevated temperatures and luminosities compared to more quiescent environments. Furthermore, we identify a temperature gradient from the W43 mini-starburst toward the starless clumps. We discuss whether the radiation impact of the nearby mini-starburst changes the fragmentation properties of the gas clumps and by that maybe favors more high-mass star formation in such an environment. The spectral line data reveal two different velocity components of the gas at 100 and 50 km s^-1. While chance projection is a possibility to explain these components, the projected associations of the emission sources as well as the prominent location at the Galactic bar – spiral arm interface also allow the possibility that these two components may be spatially associated and even interacting.

Conclusions. High-mass starless gas clumps can exist in the close environment of very active star formation without being destroyed. The impact of the active star formation sites may even allow for more high-mass stars to form in these 2nd generation gas clumps. This particular region near the Galactic bar – spiral arm interface has a broad distribution of gas velocities, and cloud interactions may be possible.