A Simultaneous 22 GHz Water and 44/95 GHz Methanol Maser Survey toward Massive Star- forming Regions

Abstract

The 22 GHz \water~and 44 / 95 GHz \methanol~masers are predominantly associated with high-mass star formation and these signposts would allow us to do statistical studies of high-mass star-forming regions. These molecules are originated from the icy mantle of dust grain and released in shocks. However we do not fully understand the role of those common masers in the process of massive star formation. The main aim of this thesis is to investigate the relationships of those masers with massive star-forming regions in a different evolutionary phase. We carried out simultaneous single-dish surveys of 22 GHz \water~and 44 and 95 GHz class I \methanol~maser transitions toward 782 massive star-forming regions. Our samples consist of Infrared Dark Clouds (IRDCs), Red MSX Sources (RMSs), high-mass protostellar objects (HMPOs), Methanol Maser Sources (MMS) and ultra-compact HII regions (UCHIIs). The overall detection rates are 32\%, 51\%, 61\%, 96\% and 67\% for IRDCs, RMSs, HMPOs, MMSs, and UCHIIs, respectively. There is an increasing trend for each detection rate of 22 GHz and 44 GHz maser emission with evolution of the central objects from IRDCs to UCHIIs. In samples of RMSs, 138 sources are located in the Methanol Multibeam (MMB) survey area and 25\% of them are associated with 6.7~GHz class~II \methanol\ masers. We detected \water~maser of high-velocity ($>$ 30\kms) features in 99 of 386 \water~maser sources(26\%). We discovered nine sources of being dominant \water~maser outflow candidates from RMS samples. Both of 44 and 95 GHz class I \methanol~masers have very similar properties in line parameters, which implies that they hold a common origin of the masing gas. We examined the relationship between the maser luminosity and physical conditions of parental clumps(cores) from ATLASGAL. There were significant ($\rho > 0.5$) correlations between the maser luminosity and the bolometric luminosity and the clump mass for all three masers. For maser sources associated with \ammonia~data, we found a increasing trends in the lindwidth and kinetic temperature with the evolution of the central objects. Using the L$_{\rm bol}$/M$_{\rm clump}$ ratio, we compared the distribution on each type of the central objects. There is no robust difference in the distribution on the combinations with threee maser species. Our investigation on the virial parameter against M$_{\rm clump}$ suggested that ATLASGAL clumps with any maser emission are more gravitationally stable than those with no maser emission in a wide range of clump mass. Like the L$_{\rm bol}$/M$_{\rm clump}$, L$_{\rm maser}$/L$_{\rm bol}$ appear to decrease as the cnetral objects evolve.