[Fe II] jets from intermediate-mass protostars in Carina

We present new HST/WFC3-IR narrowband [Fe II] images of protostellar jets in the Carina Nebula. Combined with 5 previously published sources, we have a sample of 18 jets and 2 HH objects. All of the jets we targeted with WFC3 show bright infrared [Fe II] emission, and a few H$\alpha$ candidate jets are confirmed as collimated outflows based on the morphology of their [Fe II] emission. Continuum-subtracted images clearly separate jet emission from the adjacent ionization front, providing a better tracer of the collimated jet than H$\alpha$ and allowing us to connect these jets with their embedded driving sources. The [Fe II] 1.64 $\mu$m/H$\alpha$ flux ratio measured in the jets is $\gtrsim 5$ times larger than in the adjacent ionization fronts. The low-ionization jet core requires high densities to shield Fe$^+$ against further ionization by the FUV radiation from O-type stars in the H II region. High jet densities imply high mass-loss rates, consistent with the intermediate-mass driving sources we identify for 13 jets. The remaining jets emerge from opaque globules that obscure emission from the protostar. In many respects, the HH jets in Carina look like a scaled-up version of the jets driven by low-mass protostars. Altogether, these observations suggest that [Fe II] emission is a reliable tracer of dense, irradiated jets driven by intermediate-mass protostars. We argue that highly collimated outflows are common to more massive protostars, and that they suggest the outflow physics inferred for low-mass stars formation scales up to at least $\sim8$ M$_{\odot}$.Comment: 24 pages, 23 figures, accepted for publication in MNRA

The Lifetimes of Phases in High-Mass Star-Forming Regions

High-mass stars form within star clusters from dense, molecular regions, but is the process of cluster formation slow and hydrostatic or quick and dynamic? We link the physical properties of high-mass star-forming regions with their evolutionary stage in a systematic way, using Herschel and Spitzer data. In order to produce a robust estimate of the relative lifetimes of these regions, we compare the fraction of dense, molecular regions above a column density associated with high-mass star formation, N(H2) > 0.4-2.5 x 10^22 cm^-2, in the 'starless (no signature of stars > 10 Msun forming) and star-forming phases in a 2x2 degree region of the Galactic Plane centered at l=30deg. Of regions capable of forming high-mass stars on ~1 pc scales, the starless (or embedded beyond detection) phase occupies about 60-70% of the dense, molecular region lifetime and the star-forming phase occupies about 30-40%. These relative lifetimes are robust over a wide range of thresholds. We outline a method by which relative lifetimes can be anchored to absolute lifetimes from large-scale surveys of methanol masers and UCHII regions. A simplistic application of this method estimates the absolute lifetimes of the starless phase to be 0.2-1.7 Myr (about 0.6-4.1 fiducial cloud free-fall times) and the star-forming phase to be 0.1-0.7 Myr (about 0.4-2.4 free-fall times), but these are highly uncertain. This work uniquely investigates the star-forming nature of high-column density gas pixel-by-pixel and our results demonstrate that the majority of high-column density gas is in a starless or embedded phase.Comment: 10 pages, accepted to Ap

Direct Imaging At 12 Microns Of The Star-Forming Region W51 IRS-2

Astronom

Jets, Outflows, and Explosions in Massive Star Formation

Multispectral studies of nearby, forming stars provide insights into all classes of accreting systems. Objects which have magnetic fields, spin, and accrete produce jets and collimated outflows. Jets are seen in systems ranging from brown dwarf stars to supermassive black holes. Outflow speeds are typically a few times the escape speed from the launch region - 100s of \kms\ for young stars to nearly the speed of light for black-holes. Because many young stellar objects (YSOs) are nearby, we can see outflow evolution and measure proper motions on times scales of years. Because the shocks in YSO outflows emit in atoms, ions, and molecules in addition to the continuum, many physical properties such as temperatures, densities, and velocities can be measured. Momenta and kinetic energies can be computed. YSO outflows are a major source of feedback in the self-regulation of star formation. The lessons learned can be applied to much more distant and energetic cosmic sources such as AGN and galactic nuclear super winds - systems in which evolution occurs on time-scales of hundreds to millions of years. Some dense star-forming regions produce powerful explosions. The nearest massive star-forming region, Orion OMC1, powered a $\sim 10^{48}$ erg explosion about 550 years ago (that is when the light from the event would have reached the Solar System). The OMC1 explosion was likely powered by an N-body interaction which resulted in the formation of a compact, AU-scale binary or resulted in a protostellar merger. The binary or merger remnant, the $\sim$15 \Msol\ object known as radio source I (Src I) was ejected from the core with a speed of $\sim$10 \kms\ along with two other stars. The $\sim$10~\Msol\ BN object was ejected with $\sim$30~\kms\ and a $\sim$3~\Msol\ star was ejected with $\sim$55~\kms .Comment: 21 pages, 11 figure