Physical and chemical variations within the W3 star-forming region .2. The 345 GHz spectral line survey

Results are presented of the 345 GHz spectral survey toward three sources in the W 3 Giant Molecular Cloud: W 3 IRS4, W 3 IRS5 and W 3(H2O). Nearly 90% of the atmospheric window between 334 and 365 GHz has been scanned using the James Clerk Maxwell Telescope (JCMT(1)) down to a noise level of similar to 80 mK per resolution element. These observations are complemented by a large amount of data in the 230 GHz atmospheric window. From this data set physical conditions and beam-averaged column densities are derived for more than 14 chemically different species (over 24 different isotopes). The physical parameters derived in Paper I (Helmich et al. 1994) are confirmed by the analysis of the excitation of other species, although there is evidence that the silicon- and sulfur-bearing molecules exist in a somewhat denser and warmer environment. The densities are high, greater than or equal to 10(6) cm(-3), in the three sources and the kinetic temperatures for the bulk of the gas range from 55 K for IRS4 to 220 K for W 3(H2O). The chemical differences between the three sources are very striking: silicon- and sulfur-bearing molecules such as SiO and SO2 are prominent toward IRS5, whereas organic molecules like CH3OH, CH3OCH3 and CH3OCHO are at least an order of magnitude more abundant toward W 3(H2O). Vibrationally excited molecules are also detected toward this source. Only simple molecules are found toward IRS4. The data provide constraints on the amount of deuterium fractionation and the ionization fraction in the observed regions as well. These chemical characteristics are discussed in the context of an evolutionary sequence, in which IRS5 is the youngest, W 3(H2O) somewhat older and IRS4, although still enigmatic, the oldest.