High-mass star-forming cloud G0.38+0.04 in the Galactic center dust ridge contains H₂CO and SiO masers^⋆

¹ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
e-mail: Adam.Ginsburg@eso.org
² International Centre for Radio Astronomy Research, Curtin University, GPO Box U1987, Perth WA 6845, Australia
³ Max–Planck–Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁴ Astron. Dept., King Abdulaziz University, PO Box 80203, 21589 Jeddah, Saudi Arabia
⁵ School of Physics, University of New South Wales, Sydney NSW 2052, Australia
⁶ CSIRO Astronomy and Space Science, PO Box 76, Epping, NSW 1710, Australia
⁷ National Radio Astronomy Observatory, 1003 Lopezville Rd, Socorro, NM 87801, USA
⁸ Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstraße 12-14, 69120 Heidelberg, Germany
⁹ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
¹⁰ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
¹¹ Astrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF, UK
¹² Department of Physics and Astronomy and MQ Research Centre in Astronomy, Astrophysics and Astrophotonics, Macquarie University, NSW 2109, Australia

Received: 25 September 2015
Accepted: 20 October 2015

Abstract

We have discovered a new H₂CO (formaldehyde) 1_1,0−1_1,1 4.82966 GHz maser in Galactic center Cloud C, G0.38+0.04. At the time of acceptance, this is the eighth region to contain an H₂CO maser detected in the Galaxy. Cloud C is one of only two sites of confirmed high-mass star formation along the Galactic center ridge, affirming that H₂CO masers are exclusively associated with high-mass star formation. This discovery led us to search for other masers, among which we found new SiO vibrationally excited masers, making this the fourth star-forming region in the Galaxy to exhibit SiO maser emission. Cloud C is also a known source of CH₃OH Class-II and OH maser emission. There are now two known regions that contain both SiO and H₂CO masers in the CMZ, compared to two SiO and six H₂CO in the Galactic disk, while there is a relative dearth of H₂O and CH₃OH Class-II masers in the CMZ. SiO and H₂CO masers may be preferentially excited in the CMZ, perhaps because of higher gas-phase abundances from grain destruction and heating, or alternatively H₂O and CH₃OH maser formation may be suppressed in the CMZ. In any case, Cloud C is a new testing ground for understanding maser excitation conditions.