134 research outputs found
The Life Cycle of Dust
Dust offers a unique probe of the interstellar medium (ISM) across multiple size, density, and temperature scales. Dust is detected in outflows of evolved stars, star-forming molecular clouds, planet-forming disks, and even in galaxies at the dawn of the Universe. These grains also have a profound effect on various astrophysical phenomena from thermal balance and extinction in galaxies to the building blocks for planets, and changes in dust grain properties will affect all of these phenomena. A full understanding of dust in all of its forms and stages requires a multi-disciplinary investigation of the dust life cycle. Such an investigation can be achieved with a statistical study of dust properties across stellar evolution, star and planet formation, and redshift. Current and future instrumentation will enable this investigation through fast and sensitive observations in dust continuum, polarization, and spectroscopy from near-infrared to millimeter wavelengths
The Kinematic and Chemical Properties of a Potential Core-Forming Clump: Perseus B1-E
We present 13CO and C18O (1-0), (2-1), and (3-2) maps towards the
core-forming Perseus B1-E clump using observations from the James Clerk Maxwell
Telescope (JCMT), Submillimeter Telescope (SMT) of the Arizona Radio
Observatory, and IRAM 30 m telescope. We find that the 13CO and C18O line
emission both have very complex velocity structures, indicative of multiple
velocity components within the ambient gas. The (1-0) transitions reveal a
radial velocity gradient across B1-E of 1 km/s/pc that increases from
north-west to south-east, whereas the majority of the Perseus cloud has a
radial velocity gradient increasing from south-west to north-east. In contrast,
we see no evidence of a velocity gradient associated with the denser
Herschel-identified substructures in B1-E. Additionally, the denser
substructures have much lower systemic motions than the ambient clump material,
which indicates that they are likely decoupled from the large-scale gas.
Nevertheless, these substructures themselves have broad line widths (0.4 km/s)
similar to that of the C18O gas in the clump, which suggests they inherited
their kinematic properties from the larger-scale, moderately dense gas.
Finally, we find evidence of C18O depletion only toward one substructure,
B1-E2, which is also the only object with narrow (transonic) line widths. We
suggest that as prestellar cores form, their chemical and kinematic properties
are linked in evolution, such that these objects must first dissipate their
turbulence before they deplete in CO.Comment: Accepted by ApJ, 34 pages, 12 figure
An Observed Lack of Substructure in Starless Cores II: Super-Jeans Cores
We present SMA and CARMA continuum and spectral line observations of five
dense cores located in the Perseus and Ophiuchus molecular clouds whose masses
exceed their thermal Jeans masses. Three of these cores have previously been
identified as being starless and two have been classified as being possibly
protostellar. We find that one core is certainly protostellar. The other four
cores, however, are starless and undetected in both C18O (2-1) and 1.3mm
continuum emission. These four starless cores have flat density profiles out to
at least 0.006 pc, which is typical for starless cores in general. Density
profiles predicted by some collapse models, especially in the early stages of
infall, are consistent with our observations. Archival data reveal that these
starless cores have significant non-thermal support against collapse, although
they may still be unstable.Comment: 18 pages including 5 pages of figures, accepted to Ap
Acceleration and Substructure Constraints in a Quasar Outflow
We present observations of probable line-of-sight acceleration of a broad
absorption trough of C IV in the quasar SDSS J024221.87+004912.6. We also
discuss how the velocity overlap of two other outflowing systems in the same
object constrains the properties of the outflows. The Si IV doublet in each
system has one unblended transition and one transition which overlaps with
absorption from the other system. The residual flux in the overlapping trough
is well fit by the product of the residual fluxes in the unblended troughs. For
these optically thick systems to yield such a result, at least one of them must
consist of individual subunits rather than being a single structure with
velocity-dependent coverage of the source. If these subunits are identical,
opaque, spherical clouds, we estimate the cloud radius to be r = 3.9 10^15 cm.
If they are identical, opaque, linear filaments, we estimate their width to be
w = 6.5 10^14 cm. These subunits are observed to cover the Mg II broad emission
line region of the quasar, at which distance from the black hole the above
filament width is equal to the predicted scale height of the outer atmosphere
of a thin accretion disk. Insofar as that scale height is a natural size scale
for structures originating in an accretion disk, these observations are
evidence that the accretion disk can be a source of quasar absorption systems.
Based on data from ESO program 075.B-0190(A).Comment: 14 emulateapj pages, 7 figures, ApJ in pres
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