A CS and NH3 survey of regions with H2O maser emission

We present CS (J = 1 --> 0) and NH3 (1, 1) observations toward 172 different star-forming regions (99 observed in both molecules) associated with H2O maser emission. We make a comparative study between the physical parameters obtained from the CS and NH3 spectra and their relationship with the H2O maser emission. We compare the detection rates, line intensities, line widths, and central velocities of the CS and NH3 emissions. We find a relationship between the velocity range of the H2O maser emission and its luminosity, the masers with high-velocity components being more luminous than masers without high-velocity components, which suggests that the maser-pumping mechanism is related to kinetic energy dissipated when small maser condensations move through the molecular cloud. We find that both the CS and the NH3 lines are significantly wider in regions with H2O masers than in other regions. Furthermore, for the first time, we find evidence that these line widths increase with the H2O maser luminosity. These results suggest that the presence of H2O maser emission is intrinsically associated with an increase of the thermal and turbulent energy of the ambient cloud, in agreement with the current models that propose that the H2O maser emission originates in shocked regions, such as those associated with the outflows from young stellar objects.