502 research outputs found
[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 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 and allowing us to connect these jets with their embedded driving
sources. The [Fe II] 1.64 m/H flux ratio measured in the jets is
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
M.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
Recommended from our members
Direct Imaging At 12 Microns Of The Star-Forming Region W51 IRS-2
Astronom
Carbon monoxide emission from small galaxies
A search was conducted for J = 1 yields 0 CO emission from 22 galaxies, detecting half, as part of a survey to study star formation in small to medium size galaxies. Although substantial variation was found in the star formation efficiencies of the sample galaxies, there is no apparent systematic trend with galaxy size
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