Classification and statistical properties of H2O masers

Abstract

The association between galactic H2O masers and IRAS sources from the Point Source Catalog is established for 442 sources out of a list of 505 objects, which includes all the galactic H2O masers north of 30°, known up to 1988. Using a multivariate statistical analysis on the four FIR fluxes of the associated IRAS source, galactic H2O masers are reclassified into two classes: those associated to star forming regions (SFR, 52%) and those associated to late type stars (STAR, 45%). The remaining 3% cannot be included in either class. The present classification is compared with others in the literature. Distances for a large subsample of 1120 masers are derived, using the galactic rotation curve for SFR and literature data for STAR.The parameters of the H2O maser emission (e.g. integrated flux, luminosity, variability), collected in a homogeneous way in the Arcetri H2O atlas (Comoretto et al. 1990), and those of the associated IRAS sources (e.g. flux density, luminosity, colours) are used to investigate, in a statistical way, the properties of the STAR and SFR classes. In particular, we investigate the spatial distribution of masers both in the galactic plane and perpendicular to it. We also compare the H2O and IRAS luminosities, finding a good correlation. Moreover, we find that high luminosity sources show low colour temperatures and vice versa. The spectral profile and variability are then investigated by different means. Finally, the luminosity function for each maser class is derived.