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 sour ces 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 n oise level of similar to 80 mK per resolution element. These observati ons are complemented by a large amount of data in the 230 GHz atmosphe ric window. From this data set physical conditions and beam-averaged c olumn densities are derived for more than 14 chemically different spec ies (over 24 different isotopes). The physical parameters derived in P aper I (Helmich et al. 1994) are confirmed by the analysis of the exci tation of other species, although there is evidence that the silicon- and sulfur-bearing molecules exist in a somewhat denser and warmer env ironment. 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 t he gas range from 55 K for IRS4 to 220 K for W 3(H2O). The chemical di fferences between the three sources are very striking: silicon- and su lfur-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 ex cited molecules are also detected toward this source. Only simple mole cules are found toward IRS4. The data provide constraints on the amoun t of deuterium fractionation and the ionization fraction in the observ ed regions as well. These chemical characteristics are discussed in th e context of an evolutionary sequence, in which IRS5 is the youngest, W 3(H2O) somewhat older and IRS4, although still enigmatic, the oldest .