Katharina Immer

Galactic Center

The central few hundred parsec of our Galaxy present an exceptional environment with very extreme conditions in the Milky Way. The Central Molecular Zone (CMZ) contains the so called dust ridge (e.g., Lis & Carlstrom 1994) which is a narrow ridge of dust clouds, located between the radio continuum sources G0.18-0.04 and Sgr B2. Due to the high masses (13000 - 150000 Msun) and the low dust temperatures (15 - 22 K) of the clouds, it is possible that an active site of future star formation will develop in this region. The detection of Class II methanol masers indicate the formation of high-mass stars in two of the clouds.

We observed the dust ridge region at 8.4 GHz with the Very Large Array. Analyzing the data, I detected five radio sources outside of the dust ridge clouds, in low column density regions. These sources are probably all excited by young high-mass stars. However, the existence of stars with spectral types earlier than B0.5 within the dust ridge clouds is excluded by these observations (Immer et al. 2012). The dust ridge contains the famous source M0.25+0.012 which is together with cloud "e" the most massive cloud in the ridge. Although the clouds are very similar in mass and radius, M0.25+0.012 does not contain any clear signs of high-mass star formation while cloud "e" contains a methanol masers, indicating ongoing star formation.

We obtained APEX observations of three dust ridge clouds (including M0.25+0.012 and cloud "e") as well as two other clouds in the CMZ (PI: Immer) to compare the physical conditions and chemical abundances within the clouds with and without ongoing star formation.

In another project, we are conducting proper motion observations of methanol masers in the CMZ (PI: Immer) with the VLBA to test the theory proposed by Molinari et al. (2011) who suggested that the dense and cold clouds in the CMZ are orbiting around the Galactic Center on a ring of elliptical shape.