A multifrequency study of the active star forming region NGC 6357

Abstract

We investigate the distribution of the ionized, atomic neutral and molecular gas, and of the interstellar dust in the complex star forming region NGC 6357, with the aim of studying the interplay between the massive stars and the surrounding interstellar matter. We based the study of the ionized gas on narrow-band optical images (Hα, [SII], [OIII]) obtained with the Curtis-Schmidt Camera at CTIO, Chile, and on radio continuum observations at 1465 MHz taken with the VLA, USA, with a synthesized beam of 40 seconds of arc. The distribution of the neutral atomic gas is analyzed using HI 21cm line data from the Southern Galactic Plane Survey obtained with the ATCA and Parkes radiotelescopes (synthesized beam = 2.3 minutes of arc). The distribution of the molecular gas was investigated using CO(1-0) data obtained with the Nanten radiotelescope (angular resolution = 2.7 minutes of arc), in Chile. The interstellar dust distribution was studied using infrared data from the IRAS satellite (HIRES) and MSX. The images show neutral atomic and molecular gas with velocities in the range -12 to +1 km/s associated with the outer ionized nebula. A detailed analysis of the region reveals the presence of interstellar bubbles and photodissociation regions created by the massive stars in the open cluster Pis 24 and by undiscovered ionizing sources.