Simultaneous 22 GHz water and 44 GHz methanol maser survey of ultracompact H II regions.
KIM W.-J., KIM K.-T. and KIM K.-T.
Abstract (from CDS):
We have carried out a multi-epoch simultaneous survey of 22 GHz H2O and 44 GHz Class I CH3OH masers toward 103 ultracompact H II regions (UCH IIs) between 2010 and 2017. We detected H2O and CH3OH maser emission in 74 (72%) and 55 (53%) UCH IIs, respectively. Among them, three H2O and 27 CH3OH maser sources are new detections. These high detection rates suggest that the occurrence periods of both maser species are significantly overlapped with the UCH II phase of massive star formation. The CH3OH maser lines always have small (<10 km s–1) relative velocities with respect to the natal molecular cores, while H2O maser lines often show larger relative velocities. Twenty four H2O maser-detected sources have maser lines at relative velocities >30 km s–1, and 13 of them show extremely high-velocity (>50 km s–1) components. The appearance and disappearance of H2O maser lines are quite frequent over six-month or one-year time intervals. In contrast, CH3OH maser lines usually do not exhibit significant variations in the line intensity, velocity, or shape for the same periods. The isotropic luminosities of both masers appear to correlate with the bolometric luminosities of the central stars. This correlation becomes much stronger in the case where data points in the low- and intermediate-mass regimes are added. The maser luminosities also tend to increase with the radio continuum luminosities of UCH IIs and the submillimeter continuum luminosities of the associated dense cores.