The molecular environment of NGC 3603^*

I. Spatial distribution and kinematic structure

¹ Institut für Theoretische Physik und Astrophysik, Univ. Würzburg, Am Hubland, 97074 Würzburg, Germany
² Institut de Radio-Astronomie Millimétrique, 300 rue de la Piscine DU, 38406 St. Martin-d'Hères, France
³ Departamento de Astronomía, Universidad de Chile, Casilla 36 - D, Santiago, Chile
⁴ Jet Propulsion Laboratory, California Inst. of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
⁵ Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany

Corresponding author: D. E. A. Nürnberger, nurnberg@astro.uni-wuerzburg.de

Received: 23 April 2002
Accepted: 9 July 2002

Abstract

We present CS (2–1) and CS (3–2) observations of the molecular gas associated with the Galactic starburst template NGC 3603, over an area of 58  167, with the OB cluster at the center. Total velocity integrated maps and channel maps give insight into the spatial distribution and the kinematic structure of the dense gas in the giant molecular cloud from which the starburst cluster originated. We identify 13 molecular clumps with radii less than 0.8 pc and derive upper limits for their virial masses as well as lower limits for their H₂ column densities:    (1.0 ± 0.6)  10³  and    (0.4 ± 0.2)  10²³ cm^-2. One of the clumps, MM 11, clearly stands out with a mass and column density 4 times higher than average. The CS (3–2) / CS (2–1) map shows higher intensity ratios to the south of the OB cluster than to the north (0.80 ± 0.08 versus 0.32 ± 0.11), which indicates a substantial difference in the physical conditions (either opacities or excitation temperatures) of the molecular gas. From the average of the line peak velocities, 14.2 ± 1.6 km s^-1, we deduce a kinematic distance of 7.7 ± 0.2 kpc for NGC 3603. We estimate the star formation efficiency (30%) of the central part of the NGC 3603 H ii  region. If we assume the age of the OB cluster to be less than 3 Myr and the star formation rate to be larger than 1.3  10^-3   yr^-1, the derived timescale for gas removal (τ ~ 6 Myr) can explain why the starburst cluster itself is nearly void of interstellar material. The remnant clump MM 1 appears to constitute the head of a prominent pillar which still becomes dispersed by ionizing radiation and stellar winds originating from the massive stars of the cluster. Because some of the molecular clumps are associated with near and mid infrared sources as well as OH, H₂O and CH₃OH maser sources we conclude that star formation is still going on within NGC 3603.