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S. I. Sadavoy,
J. Di Francesco,
D. Johnstone,
M. J. Currie,
E. Drabek,
J. Hatchell,
D. Nutter,
Ph. André,
D. Arzoumanian,
M. Benedettini, [......],
J. C. Mottram,
S. Pezzuto,
A. Roy,
K. Rygl,
N. Schneider-Bontemps,
L. Spinoglio,
L. Testi,
N. Tothill,
D. Ward-Thompson,
G. White
[show abstract]
[hide abstract]
ABSTRACT: We present Herschel observations from the Herschel Gould Belt Survey and
SCUBA-2 science verification observations from the JCMT Gould Belt Survey of
the B1 clump in the Perseus molecular cloud. We determined the dust emissivity
index using four different techniques to combine the Herschel PACS+SPIRE data
at 160 - 500 microns with the SCUBA-2 data at 450 microns and 850 microns. Of
our four techniques, we found the most robust method was to filter-out the
large-scale emission in the Herschel bands to match the spatial scales
recovered by the SCUBA-2 reduction pipeline. Using this method, we find beta ~
2 towards the filament region and moderately dense material and lower beta
values (beta > 1.6) towards the dense protostellar cores, possibly due to dust
grain growth. We find that beta and temperature are more robust with the
inclusion of the SCUBA-2 data, improving estimates from Herschel data alone by
factors of ~ 2 for beta and by ~ 40% for temperature. Furthermore, we find core
mass differences of < 30% compared to Herschel-only estimates with an adopted
beta = 2, highlighting the necessity of long wavelength submillimeter data for
deriving accurate masses of prestellar and protostellar cores.
03/2013;
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[show abstract]
[hide abstract]
ABSTRACT: The Pipe Nebula is a molecular cloud hosting the B59 region as its only
active star-forming clump. While the particular importance of outflows in
active star forming regions is subject of debate, the quiet nature of the gas
in B59 makes it a good site to directly see the impact of protostellar feedback
on the quiescent dense gas. Using HARP at the JCMT, we mapped the B59 region
with the J=3-2 transition of 12CO to study the kinematics and energetics of the
outflows, and 13CO and C18O to study the overall dynamics of the ambient cloud,
the physical properties of the gas, and the hierarchical structure of the
region. The B59 region has a total of 30Msun of cold and quiescent material,
mostly gravitationally bound, with narrow line widths throughout. Such low
levels of turbulence in non-star-forming sites of B59 are indicative of the
intrinsic initial conditions of the cloud. On the other hand, close to the
forming protostars the impact of the outflows is observed as a localised
increase of both line widths from 0.3 to 1 km/s, and 13CO excitation
temperatures by 2-3K. The impact of the outflows is also evident in the low
column density material which shows signs of being pushed, shaped and carved by
the outflow bow shocks as they pierce their way out of the cloud. Much of this
structure is readily apparent in a dendrogram analysis of the cloud. The low
mass of B59 together with its intrinsically quiescent gas and small number of
protostars, allows the identification of specific regions where the outflows
from the embedded sources interact the dense gas. Our study suggests that
outflows are an important mechanism for injecting and sustaining supersonic
turbulence at sub-parsec size scales. We find that less than half of the
outflow energy is deposited as turbulent energy of the gas, however this
turbulent energy is sufficient to slow down the collapse of the region.
05/2012;
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J. V. Buckle,
C. J. Davis,
J. Di Francesco,
S. F. Graves,
D. Nutter,
J. S. Richer,
J. F. Roberts,
D. Ward-Thompson,
G. J. White,
C. Brunt, [......],
B. Matthews,
H. Matthews,
J. M. C. Rawlings,
S. Sadavoy,
R. J. Simpson,
N. F. H. Tothill,
Y. G. Tsamis,
S. Viti,
J. G. A. Wouterloot,
J. Yates
[show abstract]
[hide abstract]
ABSTRACT: The Gould Belt Legacy Survey will map star-forming regions within 500 pc,
using HARP (Heterodyne Array Receiver Programme), SCUBA-2 (Submillimetre
Common-User Bolometer Array 2) and POL-2 (Polarimeter 2) on the James Clerk
Maxwell Telescope (JCMT). This paper describes HARP observations of the J = 3-2
transitions of 13CO and C18O towards Orion A. The 1500-resolution observations
cover 5 pc of the Orion filament, including OMC1 (inc. BN-KL and Orion Bar),
OMC 2/3 and OMC 4, and allow a comparative study of the molecular gas
properties throughout the star-forming cloud. The filament shows a velocity
gradient of ~1 km/s /pc between OMC 1, 2 and 3, and high velocity emission is
detected in both isotopologues. The Orion Nebula and Bar have the largest
masses and line widths, and dominate the mass and energetics of the high
velocity material. Compact, spatially resolved emission from CH3CN, 13CH3OH,
SO, HCOOCH3, C2H5OH, CH3CHO and CH3OCHO is detected towards the Orion Hot Core.
The cloud is warm, with a median excitation temperature of ~24 K; the Orion Bar
has the highest excitation temperature gas, at >80 K. The C18O excitation
temperature correlates well with the dust temperature (to within 40%). The C18O
emission is optically thin, and the 13CO emission is marginally optically
thick; despite its high mass, OMC 1 shows the lowest opacities. A virial
analysis indicates that Orion A is too massive for thermal or turbulent
support, but is consistent with a model of a filamentary cloud that is threaded
by helical magnetic fields. The variation of physical conditions across the
cloud is reflected in the physical characteristics of the dust
cores....continued
01/2012;
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[show abstract]
[hide abstract]
ABSTRACT: The complexity of the ISM is such that it is unlikely that star formation is
initiated in the same way in all molecular clouds. While some clouds seem to
collapse on their own, others may be triggered by an external event such as a
cloud/flow collision forming a gravitationally unstable enhanced density layer.
This work tests cloud-cloud collisions as the triggering mechanism for star
formation in the Serpens Main Cluster as has been suggested by previous work. A
set of smoothed particle hydrodynamics (SPH) simulations of the collision
between two cylindrical clouds are performed and compared to (sub)millimetre
observations of the Serpens Main Cluster. A configuration has been found which
reproduces many of the observed characteristics of Serpens, including some of
the main features of the peculiar velocity field. The evolution of the velocity
with position throughout the model is similar to that observed and the column
density and masses within the modeled cloud agree with those measured for the
SE sub-cluster. Furthermore, our results also show that an asymmetric collision
provides the ingredients to reproduce lower density filaments perpendicular to
the main structure, similar to those observed. In this scenario, the formation
of the NW sub-cluster of Serpens can be reproduced only if there is a
pre-existing marginally gravitationally unstable region at the time the
collision occurs. This work supports the interpretation that a collision
between two clouds may have been the trigger of the most recent burst of star
formation in Serpens. It not only explains the complicated velocity structure
seen in the region, but also the temperature differences between the north (in
"isolated" collapse) and the south (resulting from the shock between the
clouds). In addition it provides an explanation for the sources in the south
having a larger spread in age than those in the north.
01/2011;
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C. J. Davis,
A. Chrysostomou,
J. Hatchell,
J. G. A. Wouterloot,
J. V. Buckle,
D. Nutter,
M. Fich,
C. Brunt,
H. Butner,
B. Cavanagh, [......],
J. S. Richer,
J. Roberts,
S. Sadavoy,
R. J. Simpson,
N. Tothill,
Y. Tsamis,
S. Viti,
D. Ward-Thompson,
Glenn J. White,
J. Yates
[show abstract]
[hide abstract]
ABSTRACT: As part of a James Clerk Maxwell Telescope (JCMT) Legacy Survey of star formation in the Gould Belt, we present early science results for Taurus. CO J= 3 –2 maps have been secured along the north-west ridge and bowl, collectively known as L 1495, along with deep 13CO and C18O J= 3 –2 maps in two subregions. With these data, we search for molecular outflows, and use the distribution of flows, Herbig–Haro (HH) objects and shocked H2 line-emission features, together with the population of young stars, protostellar cores and starless condensations to map star formation across this extensive region. In total, 21 outflows are identified. It is clear that the bowl is more evolved than the ridge, harbouring a greater population of T Tauri stars and a more diffuse, more turbulent ambient medium. By comparison, the ridge contains a much younger, less widely distributed population of protostars which, in turn, is associated with a greater number of molecular outflows. We estimate the ratio of the numbers of pre-stellar to protostellar cores in L 1495 to be ∼1.3–2.3, and of gravitationally unbound starless cores to (gravitationally bound) pre-stellar cores to be ∼1. If we take previous estimates of the protostellar lifetime of ∼5 × 105 yr, this indicates a pre-stellar lifetime of 9(±3) × 105 yr. From the number of outflows, we also crudely estimate the star formation efficiency in L 1495, finding it to be compatible with a canonical value of 10–15 per cent. We note that molecular outflow-driving sources have redder near-infrared colours than their HH jet-driving counterparts. We also find that the smaller, denser cores are associated with the more massive outflows, as one might expect if mass build-up in the flow increases with the collapse and contraction of the protostellar envelope.
Monthly Notices of the Royal Astronomical Society 06/2010; 405(2):759 - 776. · 4.90 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: The Serpens North Cluster is a nearby low mass star forming region which is part of the Gould Belt. It contains a range of young stars thought to correspond to two different bursts of star formation and provides the opportunity to study different stages of cluster formation. This work aims to study the molecular gas in the Serpens North Cluster to probe the origin of the most recent burst of star formation in Serpens. Transitions of the C17O and C18O observed with the IRAM 30m telescope and JCMT are used to study the mass and velocity structure of the region while the physical properties of the gas are derived using LTE and non-LTE analyses of the three lowest transitions of C18O. The molecular emission traces the two centres of star formation which are seen in submillimetre dust continuum emission. In the ~40M_sun NW sub-cluster the gas and dust emission trace the same structures although there is evidence of some depletion of the gas phase C18O. The gas has a very uniform temperature (~10K) and velocity (~8.5km/s) throughout the region. This is in marked contrast to the SE sub-cluster. In this region the dust and the gas trace different features, with the temperature peaking between the submillimetre continuum sources, reaching up to ~14K. The gas in this region has double peaked line profiles which reveal the presence of a second cloud in the line of sight. The submillimetre dust continuum sources predominantly appear located in the interface region between the two clouds. Even though they are at a similar stage of evolution, the two Serpens sub-clusters have very different characteristics. We propose that these differences are linked to the initial trigger of the collapse in the regions and suggest that a cloud-cloud collision could explain the observed properties. Comment: Accepted for publication in A&A
06/2010;
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S. F. Graves,
J. S. Richer,
J. V. Buckle, A. Duarte-Cabral,
G. A. Fuller,
M. R. Hogerheijde,
J. E. Owen,
C. Brunt,
H. M. Butner,
B. Cavanagh, [......],
J. F. Roberts,
S. Sadavoy,
R. J. Simpson,
N. F. H. Tothill,
Y. G. Tsamis,
S. Viti,
D. Ward-Thompson,
G. J. White,
J. G. A. Wouterloot,
J. Yates
[show abstract]
[hide abstract]
ABSTRACT: The Gould Belt Legacy Survey (GBS) on the JCMT has observed a region of 260 square arcminutes in 12CO J=3--2 emission, and a 190 square arcminute subset of this in 13CO and C18O towards the Serpens molecular cloud. We examine the global velocity structure of the non-outflowing gas, and calculate excitation temperatures and opacities. The large scale mass and energetics of the region are evaluated, with special consideration for high velocity gas. We find the cloud to have a mass of 203 solar masses, and to be gravitationally bound, and that the kinetic energy of the outflowing gas is approximately seventy percent of the turbulent kinetic energy of the cloud. We identify compact outflows towards some of the submillimetre Class 0/I sources in the region Comment: 17 Pages, accepted by MNRAS
06/2010;
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J. V. Buckle,
E. I. Curtis,
J. F. Roberts,
G. J. White,
J. Hatchell,
C. Brunt,
H. M. Butner,
B. Cavanagh,
A. Chrysostomou,
C. J. Davis, [......],
J. M. C. Rawlings,
J. S. Richer,
S. Sadavoy,
R. J. Simpson,
N. F. H. Tothill,
Y. G. Tsamis,
S. Viti,
D. Ward-Thompson,
J. G. A. Wouterloot,
J. Yates
[show abstract]
[hide abstract]
ABSTRACT: The Gould Belt Legacy Survey will survey nearby star-forming regions (within 500 pc), using Heterodyne Array Receiver Programme (HARP), Submillimetre Common-User Bolometer Array 2 and Polarimeter 2 on the James Clerk Maxwell Telescope. This paper describes the initial data obtained using HARP to observe 12CO, 13CO and C18O J= 3 → 2 towards two regions in Orion B, NGC 2024 and NGC 2071. We describe the physical characteristics of the two clouds, calculating temperatures and opacities utilizing all the three isotopologues. We find good agreement between temperatures calculated from CO and from dust emission in the dense, energetic regions. We determine the mass and energetics of the clouds, and of the high-velocity material seen in 12CO emission, and compare the relative energetics of the high- and low-velocity material in the two clouds. We present a clumpfind analysis of the 13CO condensations. The slope of the condensation mass functions, at the high-mass ends, is similar to the slope of the initial mass function.
Monthly Notices of the Royal Astronomical Society 12/2009; 401(1):204 - 222. · 4.90 Impact Factor
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H Christie,
S Viti,
J Yates,
J Hatchell,
G A Fuller, A Duarte-Cabral,
S Sadavoy,
J V Buckle,
S Graves,
J Roberts,
D Nutter,
C Davis,
G J White,
M Hogerheijde,
D Ward-Thompson,
H Butner,
J Richer,
Di J Francesco
[show abstract]
[hide abstract]
ABSTRACT: We present a statistical comparison of CO depletion in a set of local molecular clouds within the Gould Belt using Sub-millimetre Common User Bolometer Array (SCUBA) and Heterodyne Array Receiver Programme (HARP) data. This is the most wide-ranging study of depletion thus far within the Gould Belt. We estimate CO column densities assuming local thermodynamic equilibrium and, for a selection of sources, using the radiative transfer code RADEX in order to compare the two column density estimation methods. High levels of depletion are seen in the centres of several dust cores in all the clouds. We find that in the gas surrounding protostars, levels of depletion are somewhat lower than for starless cores with the exception of a few highly depleted protostellar cores in Serpens and NGC 2024. There is a tentative correlation between core mass and core depletion, particularly in Taurus and Serpens. Taurus has, on average, the highest levels of depletion. Ophiuchus has low average levels of depletion which could perhaps be related to the anomalous dust grain size distribution observed in this cloud. High levels of depletion are often seen around the edges of regions of optical emission (Orion) or in more evolved or less dynamic regions such as the bowl of L1495 in Taurus and the north-western region of Serpens.
Monthly Notices of the Royal Astronomical Society. 422(2):968-980.
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http://dx.doi.org/10.1051/0004-6361/200913919.
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JV Buckle,
EI Curtis,
JF Roberts,
GJ White,
J. Hatchell,
C. Brunt,
HM Butner,
B. Cavanagh,
A. Chrysostomou,
CJ Davis, [......],
JMC Rawlings,
JS Richer,
S. Sadavoy,
RJ Simpson,
NFH Tothill,
YG Tsamis,
S. Viti,
D. Ward-Thompson,
JGA Wouterloot,
J. Yates
-
CJ Davis,
A. Chrysostomou,
J. Hatchell,
JGA Wouterloot,
JV Buckle,
D. Nutter,
M. Fich,
C. Brunt,
H. Butner,
B. Cavanagh, [......],
JS Richer,
J. Roberts,
S. Sadavoy,
RJ Simpson,
N. Tothill,
Y. Tsamis,
S. Viti,
D. Ward-Thompson,
GJ White,
J. Yates
-
J V Buckle,
C J Davis,
Di J Francesco,
S F Graves,
D Nutter,
J S Richer,
J F Roberts,
D Ward-Thompson,
G J White,
C Brunt, [......],
B Matthews,
H Matthews,
J M C Rawlings,
S Sadavoy,
R J Simpson,
N F H Tothill,
Y G Tsamis,
S Viti,
J G A Wouterloot,
J Yates
[show abstract]
[hide abstract]
ABSTRACT: The Gould Belt Legacy Survey will map star-forming regions within 500 pc, using Heterodyne Array Receiver Programme (HARP), Submillimetre Common-User Bolometer Array 2 (SCUBA-2) and Polarimeter 2 (POL-2) on the James Clerk Maxwell Telescope (JCMT). This paper describes HARP observations of the ensuremath Jensuremath<?iensuremath>= 3 $rightarrow$ 2 transitions of ensuremath 13ensuremath<?supensuremath>CO and Censuremath 18ensuremath<?supensuremath>O towards Orion A. The 15 arcsec resolution observations cover 5 pc of the Orion filament, including OMC 1 (including BN-KL and Orion bar), OMC 2?3 and OMC 4, and allow a comparative study of the molecular gas properties throughout the star-forming cloud. The filament shows a velocity gradient of textttchar1261 km sensuremath -1ensuremath<?supensuremath> pcensuremath -1ensuremath<?supensuremath> between OMC 1, 2 and 3, and high-velocity emission is detected in both isotopologues. The Orion Nebula and Bar have the largest masses and linewidths, and dominate the mass and energetics of the high-velocity material. Compact, spatially resolved emission from CHensuremath 3ensuremath<?subensuremath>CN, ensuremath 13ensuremath<?supensuremath>CHensuremath 3ensuremath<?subensuremath>OH, SO, HCOOCHensuremath 3ensuremath<?subensuremath>, CHensuremath 3ensuremath<?subensuremath>CHO and CHensuremath 3ensuremath<?subensuremath>OCHO is detected towards the Orion Hot Core. The cloud is warm, with a median excitation temperature of textttchar12624 K; the Orion Bar has the highest excitation temperature gas, at ensuremath>80 K. The Censuremath 18ensuremath<?supensuremath>O excitation temperature correlates well with the dust temperature (to within 40 per cent). The Censuremath 18ensuremath<?supensuremath>O emission is optically thin, and the ensuremath 13ensuremath<?supensuremath>CO emission is marginally optically thick; despite its high mass, OMC 1 shows the lowest opacities. A virial analysis indicates that Orion A is too massive for thermal or turbulent support, but is consistent with a model of a filamentary cloud that is threaded by helical magnetic fields. The variation of physical conditions across the cloud is reflected in the physical characteristics of the dust cores. We find similar core properties between starless and protostellar cores, but variations in core properties with position in the filament. The OMC 1 cores have the highest velocity dispersions and masses, followed by OMC 2?3 and OMC 4. The differing fragmentation of these cores may explain why OMC 1 has formed clusters of high-mass stars, whereas OMC 4 produces fewer, predominantly low-mass stars.
Monthly Notices of the Royal Astronomical Society. 422(1):521-541.
