Volume 563, March 2014
|Number of page(s)||26|
|Published online||12 March 2014|
Star formation sites toward the Galactic center region
The correlation of CH3OH masers, H2O masers, and near-IR green sources⋆
I. Physikalisches Institut, Universität zu Köln,
Zülpicher Str. 77, 50937
2 Department of Physics and Astronomy and Center for Interdisciplinary Research in Astronomy, Northwestern University, Evanston IL 60208, USA
3 National Radio Astronomy Observatory, 1003 Lopezville Road, Socorro NM 87801, USA
Received: 25 September 2013
Accepted: 15 January 2014
Aims. We present a study of star formation in the central molecular zone (CMZ) of our Galaxy through the association of three star formation indicators: 6.7 GHz CH3OH masers, 22 GHz H2O masers, and enhanced 4.5 μm emission (‘green’) sources. We explore how star formation in the CMZ(|ℓ| < 1.3°, |b| < 10′) compares with that of the Galactic disk (6 °> ℓ > 345°, |b| < 2°).
Methods. Using an automated algorithm, we search for green sources toward 6.7 GHz CH3OH masers detected in the Parkes Methanol Multibeam Survey. We combine these results with lists of 22 GHz H2O masers, including our Mopra survey of the CMZ.
Results. We find that the correlation of CH3OH masers with green sources is a function of Galactic latitude, with a minimum close to b = 0 and increasing with |b| (toward the central part of the Galaxy, 6 °> ℓ > 345°, |b| < 2°). We find no significant difference between the correlation rate of CH3OH masers with green sources in the CMZ and the disk. This suggests that although the physical conditions of the gas are different in the CMZ from that of the Galactic disk, once gravitational instability sets in at sufficiently high densities, signatures of star formation appear to be similar in both regions. Moreover, the detection of green sources, even at the distance of the Galactic center, shows that our technique can easily identify the early stages of star formation, especially in low-extinction regions of the Galaxy. Through the association of H2O and CH3OH masers, we identify 15 star-forming sites in the CMZ. We find a higher correlation rate of coincident H2O and CH3OH masers within the CMZ compared to the Galactic disk, indicating a difference in the maser evolutionary sequence for star-forming cores in these two regions.
Key words: ISM: clouds / ISM: molecules / stars: formation / Galaxy: center
Appendices A and B are available in electronic form at http://www.aanda.org
© ESO, 2014
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