2015A&A...584L...7G

We have discovered a new H₂CO (formaldehyde) 1₁.0-1.1₄ 82966GHz 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.