7 research outputs found
Giant Molecular Outflows Powered by Protostars in L1448
We present sensitive, large-scale maps of the CO J=1-0 emission of the L1448
dark cloud. These maps were acquired using the On-The-Fly capability of the
NRAO 12-meter telescope. CO outflow activity is seen in L1448 on parsec-scales
for the first time. Careful comparison of the spatial and velocity distribution
of our high-velocity CO maps with previously published optical and
near-infrared images and spectra has led to the identification of six distinct
CO outflows. We show the direct link between the heretofore unknown, giant,
highly-collimated, protostellar molecular outflows and their previously
discovered, distant optical manifestations. The outflows traced by our CO
mapping generally reach the projected cloud boundaries. Integrated intensity
maps over narrow velocity intervals indicate there is significant overlap of
blue- and red-shifted gas, suggesting the outflows are highly inclined with
respect to the line-of-sight, although the individual outflow position angles
are significantly different. The velocity channel maps also show that the
outflows dominate the CO line cores as well as the high-velocity wings. The
magnitude of the combined flow momenta, as well as the combined kinetic energy
of the flows, are sufficient to disperse the 50 solar mass NH3 cores in which
the protostars are currently forming, although some question remains as to the
exact processes involved in redirecting the directionality of the outflow
momenta to effect the complete dispersal of the parent cloud.Comment: 11 pages, 9 figures, to be published in the Astronomical Journa
Infall models of Class 0 protostars
We have carried out radiative transfer calculations of infalling, dusty
envelopes surrounding embedded protostars to understand the observed properties
of the recently identified ``Class 0'' sources. To match the far-infrared peaks
in the spectral energy distributions of objects such as the prototype Class 0
source VLA 1623, pure collapse models require mass infall rates
\sim10^{-4}\msunyr. The radial intensity distributions predicted by
such infall models are inconsistent with observations of VLA 1623 at sub-mm
wavelengths, in agreement with the results of Andre et al. (1993) who found a
density profile of rather than the expected gradient. To resolve this conflict, while still invoking
infall to produce the outflow source at the center of VLA 1623, we suggest that
the observed sub-mm intensity distribution is the sum of two components: an
inner infall zone, plus an outer, more nearly constant-density region. This
explanation of the observations requires that roughly half the total mass
observed within 2000 AU radius of the source lies in a region external to the
infall zone. The column densities for this external region are comparable to
those found in the larger Oph A cloud within which VLA 1623 is embedded. The
extreme environments of Class 0 sources lead us to suggest an alternative or
additional interpretation of these objects: rather than simply concluding with
Andre et al. that Class 0 objects only represent the earliest phases of
protostellar collapse, and ultimately evolve into older ``Class I'' protostars,
we suggest that many Class 0 sources could be the protostars of very dense
regions. (Shortened)Comment: 22 pages, including 3 PostScript figures, accepted for publication in
The Astrophysical Journa
Models for Multiband IR Surveys
Empirical 'backward' galaxy evolution models for IR-bright galaxies are
constrained using multiband IR surveys. A new Monte-Carlo algorithm is
developed for this task. It exploits a large library of realistic Spectral
Energy Distributions (SEDs) of 837 local IR galaxies (IRAS 25 selected)
from the UV (1000{\AA}) to the radio (20cm), including ISO-measured 3--13 unidentified broad features (UIBs). The basic assumption is that the local
correlation between SEDs and Mid-Infrared (MIR) luminosities can be applied to
earlier epochs of the Universe. Three populations of IR sources are considered
in the evolution models. These include (1) starburst galaxies, (2) normal
late-type galaxies, and (3) galaxies with AGN. A set of models so constructed
are compared with data from the literature. Predictions for number counts,
confusion limits, redshift distributions, and color-color diagrams are made for
multiband surveys using the upcoming SIRTF satellite.Comment: 40 pages latex. 32 GIF figures. New Version (July 8, 2001) to be
accepted by ApJ. High quality figures (included in a PS file of the paper)
can be found in
http://spider.ipac.caltech.edu/staff/cxu/papers/paper_model_3.ps.g