IRAS 05358+3543: Multiple outflows at the earliest stages of massive star formation

We present a high-angular-resolution molecular line and millimeter continuum study of the massive star formation site IRAS 05358+3543. Observations with the Plateau de Bure Interferometer in CO 1-0, SiO 2-1 and (HCO+)-C-13 1-0 reveal at least three outflows which cannot be separated in single-dish data. Observations at millimeter and sub-millimeter wavelengths from the IRAM 30 m telescope and the CSO provide additional information on the region. The most remarkable feature is a highly collimated (collimation factor similar to10) and massive (>10 M.) bipolar outflow of similar to1 pc length, which is part of a quadrupolar outflow system. The three observed molecular outflows forming the IRAS 05358+3543 outflow system resemble, in structure and collimation, those typical of low-mass star-forming regions. They might therefore, just like low-mass outflows, be explained by shock entrainment models of jets. We estimate a mass accretion rate of similar to10(-4) M./yr, sufficient to overcome the radiative pressure of the central object and to build up a massive star, lending further support to the hypothesis that massive star formation occurs similarly to low-mass star formation, only with higher accretion rates and energetics. In the millimeter continuum, we find three sources near the center of the quadrupolar outflow, each with a mass of 75-100 M.. These cores are associated with a complex region of infrared reflection nebulosities and their embedded illuminating sources. The molecular line data show that SiO is found mostly in the outflows, whereas (HCO+)-C-13 traces core-like structures, though likely with varying relative abundances. Thermal CH3OH comprises both features and can be disentangled into a core-tracing component at the line center, and wing emission following the outflows. A CO line-ratio study (using data of the J = 1-0, 2-1 and 6-5 transitions) reveals local temperature gradients.