Molecular Outflows in Star Forming Regions

Abstract

This thesis work focus on the study of the molecular emission from outflows produced by jets in regions of star formation. After introducing the topic of star formation, and in particular its related outflow process, a series of studies performed in the millimeter and sub-millimeter wavelengths range are presented, including regions of low-, intermediate-, and high-mass.<br /> Using the Submillimeter Array the SiO, H_2CO, and CH_3OH lines were observed in a prototypical low-mass protostellar outflow. These observations revealed a small scale stratification of the different molecular species, with the SiO mainly tracing the principal bow-shock in the region. However, the kinematic structure at the main bow-shock position is different from that expected in a single bow shock. It is proposed that the high-velocity SiO clump at such position is kinetically independent from the low-velocity gas. The analysis of the SiO emission allowed the determination of the physical conditions of the emitting gas, showing that the the high velocity SiO clumps consist of high density gas, with values comparable to the density of the bullets in the extremely high velocity (EHV) jets. It is proposed that the high-velocity SiO clumps in L1157 have the same origin as the EHV bullets. <br /> The so-called mid-J CO lines (CO J=6-5, J=7-6) were observed with the APEX telescope towards regions of low-, intermediate-, and high-mass star formation. The warm gas traced by these transitions was particularly found in the high-velocity gas close to the exciting source and in the terminal bow shocks, suggesting that energetic processes are at work in these environments and are especially traced by these lines. A relevant result obtained from the mid-J CO observations is that even at low velocities the emission clearly defines the outflow structures, which is remarkably different from what we see in low-J CO lines. The latter allowed to identify outflows whose axis are close to the plane of the sky, particularly important in region of high-mass star formation. In addition, an EHV outflow was unveiled only by the mid-J CO observations, suggesting that this kind of outflow are particularly traced by mid-J CO lines. Therefore, the overall picture presented by the mid-J CO observations in protostellar outflows is a tendency to trace the most excited regions within them, i.e. the jet component and the terminal bow shocks. Also, the mid-J CO lines have proven to be good tracers of the low-velocity emission in outflows, as well as important tracers of highly excited extremely high velocity emission.<br /> One of the first high spectral resolution observations of high-J CO lines are also presented in this thesis. The high-J CO lines at terahertz frequencies (CO J=12-11, J=13-12), observed with the GREAT instrument on the SOFIA telescope, proved to be important tracers of molecular bullets in the intermediate-mass outflow studied here. In addition to be prominent in the high-velocity bullets, the high-J CO emission was also found at low velocities, which means that previous assumptions made for spectrally unresolved observations that the high-J CO emission in protostellar outflows is produced only at high velocities must be revisited.