The James Clerk Maxwell Telescope legacy survey of nearby star?forming regions in the Gould Belt

Abstract

This paper describes a James Clerk Maxwell Telescope (JCMT) legacy survey that has been awarded roughly 500 hr of observing time to be carried out from 2007 to 2009. In this survey, we will map with SCUBA-2 (Submillimetre Common-User Bolometer Array 2) almost all of the well-known low-mass and intermediate-mass star-forming regions within 0.5 kpc that are accessible from the JCMT. Most of these locations are associated with the Gould Belt. From these observations, we will produce a flux-limited snapshot of star formation near the Sun, providing a legacy of images, as well as point-source and extended-source catalogs, over almost 700 deg(2) of sky. The resulting images will yield the first catalog of prestellar and protostellar sources selected by submillimeter continuum emission, and should increase the number of known sources by more than an order of magnitude. We will also obtain with the array receiver HARP (Heterodyne Array Receiver Program) CO maps, in three CO isotopologues, of a large typical sample of prestellar and protostellar sources. We will then map the brightest hundred sources with the SCUBA-2 polarimeter (POL-2), producing the first statistically significant set of polarization maps in the submillimeter. The images and source catalogs will be a powerful reference set for astronomers, providing a detailed legacy archive for future telescopes, including ALMA, Herschel, and JWST.

Full text

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arXiv:0707.0169v1 [astro-ph] 2 Jul 2007
The James Clerk Maxwell Telescope Legacy Survey of Nearby
Star-forming Regions in the Gould Belt
D. Ward-Thompson1, J. Di Francesco2, J. Hatchell3, M. R. Hogerheijde4, P. Bastien5, S.
Basu6, I. Bonnell7, J. Bowey8, C. Brunt3, J. Buckle9, H. Butner10, B. Cavanagh11, A.
Chrysostomou11,12, E. Curtis9, C. J. Davis11, W. R. F. Dent13, E. van Dishoeck4, M. G.
Edmunds1, M. Fich14, J. Fiege15, L. Fissel16, P. Friberg11, R. Friesen2,17, W. Frieswijk18, G.
A. Fuller19, A. Gosling20, S. Graves9, J. S. Greaves7, F. Helmich18, R. E. Hills9, W. S.
Holland13, M. Houde6, R. Jayawardhana16, D. Johnstone2,17, G. Joncas21, H. Kirk2,17, J. M.
Kirk1, L. B. G. Knee2, B. Matthews2, H. Matthews22, C. Matzner16, G. H.
Moriarty-Schieven2,11D. Naylor23, D. Nutter1, R. Padman9, R. Plume24, J. M. C.
Rawlings8, R. O. Redman2, M. Reid25, J. S. Richer9, R. Shipman4, R. J. Simpson1, M.
Spaans4, D. Stamatellos1, Y. Tsanis8, S. Viti8, B. Weferling11, G. J. White26,27, A. P.
Whitworth1, J. Wouterloot11, J. Yates8, M. Zhu2,11

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1School of Physics & Astronomy, Cardiff University, 5 The Parade, Cardiff, UK
2Herzberg Institute of Astrophysics,National Research Council of Canada, 5071 West
Saanich Road, Victoria, BC, Canada
3School of Physics, University of Exeter, Stocker Road, Exeter, UK
4Leiden Observatory, Leiden University, PO Box 9513, 2300 RA, Leiden, The Netherlands
5D´ epartement de physique et Observatoire due Mont-M´ egantic, Universit´ e de Montr´ eal,
C.P. 6128, Succ. Centre-ville, Montr´ eal, QC, Canada
6Physics and Astronomy Department, University of Western Ontario, 1151 Richmond
Street, London, ON, Canada
7Scottish Universities Physics Alliance, Physics & Astronomy, University of St Andrews,
North Haugh, St Andrews, Fife, UK
8Dept of Physics & Astronomy, University College London, Gower Street, London, UK
9Cavendish Laboratory, Cambridge University, J J Thomson Avenue, Cambridge, UK
10Department of Physics and Astronomy, James Madison University, 901 Carrier Drive,
Harrisonburg, VA 22807, USA
11Joint Astronomy Center, 660 N. A’Ohoku Drive, University Park, Hilo, Hawaii
12School of Physics, Astronomy and Mathematics, University of Hertfordshire, College
Lane, Hatfield, UK
13UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh, UK
14Dept of Physics & Astronomy, University of Waterloo, Waterloo, ON, Canada
15Dept of Physics and Astronomy, University of Manitoba, Winnipeg, MB, Canada
16Department of Astronomy and Astrophysics, University of Toronto, 50 St. George St.,
Toronto, ON, Canada
17Dept of Physics & Astronomy, University of Victoria, 3800 Finnerty Rd., Victoria, BC,
Canada
18SRON, Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen,

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Received
;accepted
Draft version, 2007, May 23
The Netherlands
19School of Physics & Astronomy, University of Manchester, Sackville Street, Manchester,
UK
20Astrophysics Group, Department of Physics, Oxford University, Denys Wilkinson Build-
ing, Keble Road, Oxford, UK
21Dept de Physique et Observatoire du Mont Megantic, Universite Laval, QC, Canada
22National Research Council of Canada, Dominion Radio Astrophysical Observatory, 717
White Lake Rd., Penticton, BC, Canada
23Department of Physics, University of Lethbridge, 4401 University Dr., Lethbridge, AB,
Canada
24Dept of Physics & Astronomy, University of Calgary, 2500 University Drive, Calgary,
AB, Canada
25Department of Physics & Astronomy, McMaster University, 1280 Main St. W., Hamil-
ton, ON, Canada
26Dept of Physics and Astronomy, Open University, Walton Hall, Milton Keynes, UK
27Science and Technology Facilities Council, Rutherford Appleton Laboratory, Chilton,
Didcot, UK

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ABSTRACT
This paper describes a James Clerk Maxwell Telescope (JCMT) legacy sur-
vey that has been awarded roughly 500 hrs of observing time to be carried out
from 2007 to 2009. In this survey we will map with SCUBA-2 (Submillimetre
Common User Bolometer Array 2) almost all of the well-known low-mass and
intermediate-mass star-forming regions within 0.5kpc that are accessible from
the JCMT. Most of these locations are associated with the Gould Belt. From
these observations we will produce a flux-limited snapshot of star formation near
the Sun, providing a legacy of images, as well as point-source and extended-source
catalogues, over almost 700 square degrees of sky. The resulting images will yield
the first catalogue of prestellar and protostellar sources selected by submillime-
tre continuum emission, and should increase the number of known sources by
more than an order of magnitude. We will also obtain CO maps with the array
receiver HARP (Heterodyne Array Receiver Programme), in three CO isotopo-
logues, of a large typical sample of prestellar and protostellar sources. We will
then map the brightest hundred sources with the SCUBA-2 polarimeter (POL-2),
producing the first statistically significant set of polarization maps in the sub-
millimetre. The images and source catalogues will be a powerful reference set for
astronomers, providing a detailed legacy archive for future telescopes, including
ALMA, Herschel and JWST.
Subject headings: ISM

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1.Introduction
1.1.Nearby star formation
Understanding star formation is a crucial goal of astronomy. Star formation plays a
pivotal role in most aspects of astronomy from the formation and evolution of galaxies to
the origins of extra-solar planets and the potential for life elsewhere in our Galaxy. Our
knowledge of the star-formation process has increased dramatically due to the advent of
sensitive far-infrared and submillimetre detectors but has suffered from the piece-meal
fashion in which such observations have been undertaken to date. We describe here a
project that aims to produce a large and unbiased sample of star-forming molecular material
in the solar vicinity at relatively high resolution (8–14 arcsec).
To understand star formation, we need to probe the physical conditions of molecular
clouds before and during the star formation process. Although near-IR images can tell us a
great deal about the results of star formation, the objects visible are too old to assess the
crucial conditions in which star formation originates. We need to illuminate the earliest
conditions in order to understand the formation process (e.g. Di Francesco et al., 2007;
Ward-Thompson et al., 2007).
Submillimetre continuum imaging selects the very earliest stages of star formation
because it traces the high column densities of dust, even when that dust is at low
temperatures, within star-forming cores and allows important physical parameters such as
density to be traced in detail. From its earliest days the James Clerk Maxwell Telescope
(JCMT) has been mapping submillimetre continuum emission from star-forming regions
(e.g. Ward-Thompson et al., 1989; 1995). The JCMT identified first the youngest known
protostars (Class 0 objects; Andr´ e et al. 1993) and molecular cloud cores on the verge of
collapse to form protostars (prestellar cores; Ward-Thompson et al. 1994).

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The JCMT also helped determine that the prestellar core mass function mimics the
IMF, indicating that it may be determined at the very beginning of the star formation
process – this was the first observational breakthrough in understanding its origin in nearly
50 years (Johnstone et al. 2000; Motte et al. 2001; Nutter & Ward-Thompson 2007). Many
large area continuum mapping surveys have also been carried out with the Submillimetre
Common-User Bolometer Array (SCUBA) on JCMT of star-forming regions (e.g. Johnstone
& Bally 1999; Pierce-Price et al., 2000; Johnstone et al., 2000; 2001; 2006; Hatchell et
al., 2005; 2007; Nutter et al., 2005; 2006; Nutter & Ward-Thompson 2007; J. Kirk et al.,
2005; Moriarty-Schieven et al., 2006). Many of these regions lie in a ring around the sky,
coincident with the Gould Belt.
1.2.The Gould Belt
The Gould Belt is a ring of nearby O-type stars inclined at about 20◦to the Galactic
Plane. It was first discovered in the southern hemisphere in fact by John Herschel (1847),
who noted that many of the brightest stars in the southern sky lie in a band that is inclined
to the plane of the Galaxy. Subsequently, Gould (1879) traced the northern part of the
band, thereby completing the ring.
The Gould Belt is centred on a point ∼ 200pc from the Sun and is about 350 pc in
radius (e.g. Clube 1967; Stothers & Frogel 1974; Comeron et al. 1992; de Zeeuw et al.,
1999; P¨ oppel 2001). Figure 1 shows a schematic of the Gould Belt, and Figure 2 shows its
projection onto the plane of the sky, showing the inclination to the Galactic Plane.
The formation mechanism of the Belt remains something of a mystery. One hypothesis
is that it may be the result of a high velocity cloud impacting the Galactic Plane (Comeron
& Torra, 1992; 1994; Guillout et al., 1998). An alternative possibility is a local massive

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supernova remnant or stellar wind interacting with a large molecular cloud (Blaauw 1991).
Whatever the cause, the Gould Belt is a highly active ring of nearby star formation,
and most of the local star-forming molecular clouds are associated with it, including
Taurus, Auriga, Orion, Lupus, Ophiuchus, Scorpius, Serpens and Perseus. Study of the star
formation within the Gould Belt sheds light on the process of star formation within these
respective clouds. Moreover, it may also help to shed light on the whole of the Gould Belt
itself. For example, accurate dating of the bursts of star formation around the Belt may be
able to test the various formation mechanisms of the Gould Belt.
1.3. A new era for JCMT
The JCMT is currently undergoing a complete overhaul of its instrumentation,
including a new bolometer array camera, the Submillimetre Common-User Bolometer
Array 2 (SCUBA-2; Holland et al., 2006), with an imaging polarimeter, the SCUBA-2
Polarimeter (POL-2; Bastien et al., 2005), and a heterodyne array receiver, the Heterodyne
Array Receiver Programme for B-band (HARP; Smith et al., 2003). The combination of
SCUBA-2, HARP, and POL-2 are a powerful tool set with which to study star formation.
SCUBA-2 is an innovative 10,000 pixel submillimetre camera due to be delivered
shortly to the JCMT. The camera is expected to revolutionize submillimetre astronomy
in terms of its ability to carry out wide-field surveys to unprecedented depths. SCUBA-2
uses Transition Edge Super-conducting (TES) bolometer arrays, which come complete
with in-focal-plane Superconducting Quantum Interference Device (SQUID) amplifiers and
multiplexed readouts, and are cooled to 100mK by a liquid cryogen-free dilution refrigerator.
SCUBA-2 will observe simultaneously at 850 and 450 microns, with angular resolutions of
14 and 8 arcsec respectively (Holland et al., 2006).

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The polarimeter POL-2 will have an achromatic continuously rotating half-wave plate
in order to modulate the signal at a rate faster than atmospheric transparency fluctuations.
Such a modulation should improve significantly the reliability and accuracy of submillimetre
polarimetric measurements. The signal will be analyzed by a wire-grid polarizer. For
calibration, a removable polarizer will also be available. The components, in the order that
the radiation will encounter them, are the calibration polarizer, the rotating wave plate,
and the polarizer. The components will be mounted in a box fixed permanently in front of
the entrance window of the main cryostat of SCUBA-2. All components will be mounted so
that they can be taken in and out of the beam remotely, making it very easy and fast to
start polarimetry at the telescope (Bastien et al., 2005).
HARP is a 350GHz, 4×4 element, heterodyne focal plane array, using SIS detectors,
recently commissioned on the JCMT. Working in conjunction with the backend Auto-
Correlation and Spectral-line Imaging System (ACSIS; Hovey et al., 2000), HARP provides
3-dimensional imaging capability with high sensitivity at 325 to 375GHz. This is the
first submillimetre spectral imaging system on JCMT, affording significantly improved
productivity in terms of speed of mapping. The core specification for the array is that
the combination of the receiver noise temperature and beam efficiency, weighted optimally
across the array is <330K single side-band (SSB) for the central 20GHz of the tuning range
(Smith et al., 2003). The 16 pixels have receiver temperatures of 94–165 K. The angular
resolution of HARP is 14 arcsec, matching the 850-µm resolution of SCUBA-2.
ACSIS has 16 inputs (actually 32, paired up), with a maximum bandwidth per channel
of approximately 2GHz in a 2×1 GHz configuration. It has a minimum sample time of 50ms
and a maximum output map size of 16 Gbytes. It has a number of spectral bandwidths and
resolutions that can be selected by the user: 250MHz bandwidth with 30kHz resolution;
500MHz bandwidth with 61kHz resolution (multi-subsystem mode); 1GHz bandwidth with

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500kHz resolution; and 2GHz bandwidth with 1000kHz resolution (merged). In practise,
the usable bandwidth will be about 10% less than this, because of the filter roll-off.
ACSIS and HARP together have a number of observing modes, including raster
mapping with position switching for mapping large areas, chopped jiggle mapping for fully
sampled mapping of areas comparable to the HARP focal plane area, and jiggle mapping
with fast frequency switching for fully sampled mapping of compact areas where no nearby
off-source reference position is available.
During the planning phase of observations with the new JCMT instrumentation,
numerous ideas were put forward for science questions that could be addressed (e.g.
Ward-Thompson 2004). From these plans a number of proposals emerged. One such
proposal, described herein, was to map local star-forming regions with SCUBA-2, HARP
and POL-2. This was one of seven proposals accepted as part of the JCMT Legacy
Programme.
With the increased mapping speed of SCUBA-2, one can cover essentially all of the
star-forming regions within 0.5kpc in a reasonable amount of time, detecting all of the
protostars and prestellar cores. SCUBA-2 is designed to have increased sensitivity in each
pixel, but also has two orders of magnitude more pixels than SCUBA, giving it about a
1000-fold increase in mapping speed. The increased mapping speed of SCUBA-2 can be
illustrated by comparison with the large-scale mapping survey carried out by SCUBA of
the Galactic Centre (Pierce-Price et al., 2000), which took ∼50 hours of telescope time and
covered only 1.4 square degrees. By contrast this survey with SCUBA-2 will cover roughly
700 square degrees to a greater depth in ∼120 hours.
We will use SCUBA-2 to map the submillimetre continuum emission from as many
clouds within 0.5 kpc as are visible from the JCMT, including several well known Gould
Belt clouds such as Orion, Taurus, Perseus, and Ophiuchus. Several objects outside of

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the Gould Belt, including nearby Bok Globules, will also be mapped (c.f. Launhardt et
al., 1997). We estimate that the source catalogue that we will produce will contain over
five thousand sources. Such large samples of protostars and starless cores are required to
provide robust statistics on objects over a range of evolutionary stages. With SCUBA-2’s
predicted improvement in per-pixel sensitivity over SCUBA, we will measure the prestellar
clump mass functions down to substellar masses.
HARP increases the heterodyne mapping speed of the JCMT by over an order of
magnitude. We will use this increased mapping speed to map a significant fraction of the
SCUBA-2 sources in isotopologues of CO. The combination of dust continuum maps from
SCUBA-2 plus spectral line data cubes from the heterodyne array at matched resolution
will be extremely powerful. Since molecular clouds are highly turbulent, and star formation
generates infall, outflow, and rotational motions, velocity measurements are critical in
understanding the mass-assembly process, feedback, and star-formation efficiency (e.g.
Goodwin et al., 2004a & b; Vazquez-Semadeni et al., 2005). In addition, another use of the
HARP data will be a determination of the amount of line contamination in the SCUBA
data. Johnstone et al. (2003) considered this problem in Orion and argued that it was
not significant except for faint sources. With the increased sensitivity of SCUBA2 such
contamination may be important.
POL-2 will be able to make polarization maps of both high and low density material in
molecular clouds. We will use it to map one hundred bright sources found in the SCUBA-2
survey. At present there is a debate over the relative importance of magnetic fields and
turbulence in regulating the star formation process (e.g. Mouschovias 1991; Padoan &
Nordlund 2002). Combined with kinematics from HARP, the POL-2 observations will allow
for an investigation into the balance between gravity, turbulent support, and magnetic
fields over a statistically meaningful number of star-forming cores. Previously only a few

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cores have been mapped (e.g., Holland et al., 1999; Ward-Thompson et al., 2000; Matthews
& Wilson 2002; Crutcher et al., 2004; J. Kirk et al., 2006).
The goal of this paper is to outline the aims of the Gould Belt Survey and to describe
the observations that will be carried out. In total this programme will take roughly 1000
hours of observing time on the JCMT, 500 of which have been allocated over the first two
years between 2007/8 and 2009/10. Section 2 details the SCUBA-2 aspects of the survey,
section 3 discusses the HARP survey, section 4 describes the survey to be carried out with
POL-2, section 5 outlines some surveys at far-infrared wavelengths being carried out in
parallel with this survey, and section 6 provides a brief summary of the paper.
2.SCUBA-2 Survey
To obtain a complete view of the star formation in the Gould Belt, we need an inventory
of all protostellar objects contained in these clouds. We will map with SCUBA-2 all of the
star-forming regions within 0.5 kpc in the Gould Belt accessible by the JCMT. The sample,
which includes many well-known regions, will provide a very significant snapshot of star
formation near the Sun. We will map the thermal dust emission at 850 microns towards
the AV > 1 areas of our target clouds (see Table 1) to a uniform depth, with a resolution of
14 arcsec. In higher extinction regions (AV > 3), we will go deeper, and will utilize better
weather to observe at both 850 and 450 microns – the latter has a superior resolution of 8
arcsec.
Table 1 lists details of the main clouds to be mapped, and Figures 3 – 12 illustrate the
approximate mapping areas. This will provide a legacy of images, as well as point-source
and extended-source catalogues, of roughly 700 square degrees of sky. These maps will be
sensitive to every Class 0 & I protostar in the Gould Belt and every L1544-like prestellar

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core within 200 pc (J. Kirk et al., 2005). The maps will yield the first extensive catalogue of
such objects selected by submillimetre continuum emission and will increase the number of
known sources by more than an order of magnitude. Comparison with observations taken
at other wavelengths, such as with Spitzer or Herschel, will allow correct classification of
the sources.
The key science goals of the SCUBA-2 survey are:
• to calculate the duration of each of the protostellar stages;
• to elucidate the nature of the evolution of protostellar collapse;
• to discover the origin of the initial mass function (IMF) of stars from intermediate-mass
stars to sub-stellar objects;
• to discern the connection between protostars and the molecular cloud structure from
which they formed.
In addition, the SCUBA-2 maps will provide ‘finding charts’ both for the other
aspects of this survey and for future projects. SCUBA-2 will take this subject beyond the
source-by-source approach of the past, into the domain where large-number statistics on
the earliest stages of star formation can finally be carried out, through a wide census of
starless and prestellar cores and protostars.
To avoid mapping large areas of blank sky, molecular clouds have been pre-selected
by visual extinction, AV, from the recent extinction atlas of Dobashi et al. (2005). The
continuum mapping will be divided into two layers, a wide survey of areas with AV = 1-3,
and a deep survey of area with AV > 3. Figures 3–12 show the extents of each of the
surveys in each region. In addition, some ‘blank field’ areas will also be mapped as a control
sample.

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2.1.Shallow Survey
For the shallow survey, we will map areas with AV > 1 at 850µm to a depth of 1 σ =
10 mJybeam−1. Within the Gould Belt, this comprises an area of ∼400 square degrees.
In addition, we will map 120 square degrees outside of the major star-forming complexes,
but positionally associated with the Gould Belt. This will cover nearby small clouds and
isolated star formation regions selected from dark cloud catalogues (e.g. Lynds 1962;
Cambresy 1999; Dobashi et al., 2005) and previous catalogues (e.g. Clemens & Barvainis
1988; Jijina et al. 1999; Lee & Myers 1999; Visser et al. 2002).
Finally, we will map ∼10 square degrees of blank sky (i.e. AV < 1) split into several
fields near the Gould Belt to the same depth. This will act as a control sample to see if we
have missed significant numbers of objects by using AV to select our target regions. The
data from the shallow survey will be sensitive at 3 σ to masses down to the sub-stellar mass
limit of 0.08 M⊙per beam for objects at 0.5 kpc that have Td≥ 20K, which is typical of
the low extinction parts of molecular clouds.
2.2.Deep Survey
Temperatures vary within molecular clouds and the inner regions are colder (Td∼
10K) than the outer regions (Td∼ 20K) due to increased shielding from the interstellar
UV field. For the deep survey we will map regions with AV > 3 to a depth of 1 σ = 3
mJybeam−1at 850µm to ensure a complete census of star-forming cores. These regions
comprise an area of ∼64 square degrees. These data will also reach the sub-stellar mass
limit of 0.08 M⊙per beam at 3 σ for objects at 0.5kpc at Td= 10K.
Furthermore, these observations will simultaneously provide maps at 450µm with a
mean 1 σ rms of 12 mJy per 450µm beam (i.e. equal to 6 mJy per 850µm beam after

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smoothing). This is because this aspect of the survey will be carried out in ‘Grade 1’
weather conditions (τ225GHZ≤ 0.05). The 450µm and 850µm data together will provide
spectral index information, where it is essential to have comparable resolution, to constrain
the dust opacity indices and thus the masses of the objects.
2.3. Source Count Predictions
The total star formation rate for clouds within 0.5 kpc is ∼6 × 10−3M⊙yr−1(e.g.
McKee & Williams 1997). Using the measured IMF (e.g. Kroupa 2001), the total stellar
production rate within this distance is therefore ∼0.02 stars yr−1. The best current
estimates of the timescales for prestellar cores and Class 0 protostars are ∼3 × 105yr and
∼3 × 104yr respectively (e.g. Andr´ e et al., 2000). Thus, we expect ∼6000 prestellar cores
and ∼600 Class 0 protostars to be found in our wide survey. Even allowing for possible
uncertainties in these by factors of ∼2, we would still expect thousands of objects in total,
with hundreds at low mass (M < 0.5M⊙) and tens at high-mass (M > 8M⊙).
These objects will fill in the under-populated extremes of currently measured mass
functions. Note that only tens of Class 0 protostars and hundreds of prestellar cores in
total are currently known (Andr´ e et al., 2000). Finally, the expected numbers of objects
at the mass function peak (M ≈ 0.5M⊙) will be large enough (∼20-50 in each cloud) to
reveal statistically if differences in characteristic stellar masses that exist between clouds
are caused by local environmental influences on core formation such as cloud density and
sound speed.

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2.4. Protostellar Lifetimes and Accretion Rates
The census of prestellar cores and protostars from the continuum mapping will allow
us to calculate the relative duration of these stages. Since half of the envelope mass is
accreted during the Class 0 stage and the rest during the Class I stage (Andr´ e et al., 1993),
the duration of each stage tells us about the protostellar accretion rate. For instance, if
they are roughly equal then the accretion rate is probably constant, as in the Shu collapse
model (Shu 1977).
Alternatively, if the Class 0 duration is only one-tenth the Class I duration, as is
currently suspected (Andr´ e et al., 2000), then accretion must start very rapidly and
decrease over time (e.g. Whitworth & Ward-Thompson 2001), implying a very different
collapse scenario. In addition, if much of the envelope mass is ejected (e.g. Matzner &
McKee 2000), then the fractions accreted will sum to less than 1. Current observations are
limited by small-number statistics (e.g. Visser et al. 2002) but the wide survey will provide
a sufficiently large sample to answer this question.
Furthermore, the relative quantities of prestellar cores at varying degrees of central
condensation (given by continuum radial profiles) will inform models that predict the onset
of protostellar collapse (e.g. turbulent dissipation vs. magnetic regulation).
2.5.Origin of the IMF
With the census of nearby prestellar cores provided by the continuum mapping, we
will be able to plot a very well-populated mass spectrum of these objects over a very wide
range of masses. This will allow us to confirm or refute the claim that this mass function
(e.g. Motte et al. 2001; Johnstone et al., 2006; Nutter & Ward-Thompson 2007) mimics the
stellar IMF (Salpeter 1955). Recent observations appear to show that the prestellar core