Local Star Formation: the JCMT Gould's Belt Legacy Survey
THIS LEGACY SURVEY WILL BEGIN IN 2007 AND IN THE FIRST INSTANCE
RUN THROUGH 2008
THE PLAN IS TO CONTINUE THE SURVEY THROUGH
FIGURE 1: Gould's Belt superimposed on to an IRAS 100 micron emission map.
FIGURE 2: A schematic of Gould's Belt
Most star formation within 0.5 kpc lies in Gould's Belt, a ring
around the sky containing star-forming molecular clouds centred on a
point 200 pc from the Sun and tilted at 20 degrees to the Galactic
Plane (Figures 1 and 2).
The aim of the JCMT Gould's Belt Legacy Survey is to use
SCUBA-2 and HARP-B at the JCMT to map the submillimetre continuum
emission and CO line emission from as many clouds within 0.5 kpc as
possible. The survey will include several well known Gould's Belt
clouds: Orion, Taurus, Perseus, and Ophiuchus, as well as several
objects outside of Gould's Belt, including nearby Bok Globules. To
maximize the scientific return of the SCUBA-2 observations, molecular
clouds will be preselected by visual extinction, Av, from the recent
all-Galaxy extinction atlas of Dobashi (2005). Additional information
on the identified star-forming cores will be obtained via molecular
line observations with HARP-B, and with SCUBA-2 Polarimetric
We will map almost all star-forming regions within 0.5 kpc that
are accessible to the JCMT (outlined in the table at the bottom of the
page). Most of the target regions are within Gould's belt. The sample,
which includes many well-known regions, will provide a very
significant snapshot of star formation near the Sun. The survey will
provide a legacy of images, as well as point and extended-source
catalogues, covering roughly 700 square degrees of sky.
The mapping will be divided into two layers, a wide survey of areas
with Av = 1-3, and a deeper survey of area with Av > 3. These maps
will be sensitive to every Class 0 and Class I protostar and every "L
1544-like" pre-stellar core (see e.g. Figures 3 and 4), yielding the
first catalogue of such objects selected by submillimetre continuum
emission and increasing the number of known sources from tens to
Within the field of low-mass star formation, many unresolved issues
will be addressed, including; the duration of its various stages, the
evolution of protostellar collapse, the origin of the initial mass
function (IMF) from intermediate-mass stars to sub-stellar objects,
and the connection between protostars and the molecular cloud
structure from which they are formed. The SCUBA-2 observations will
also provide finding charts for the other aspects of this survey
(described below), and will be a detailed resource for users of future
telescopes (ALMA, Herschel, JWST and beyond).
FIGURE 3: A SCUBA map of Ophiuchus
in 850 micron continuum emission (Johnstone, Di Francesco, & Kirk
2004). This is currently the largest single map of a star-forming
region made in the submillimetre. Note that the compact structures are
confined to very specific regions.
FIGURE 4: A contour map of Ophiuchus, obtained from R-band extinction mapping by
Cambresy (1999). The areas to be mapped with SCUBA-2 are highlighted
in yellow (Av = 1-3) and red (Av > 3). Only the central region was mapped by
Johnstone et al. with SCUBA (Figure 3); clearly a large portion of
the cloud remains to be observed. The SCUBA-2 map will also be at least four
times more sensitive than the SCUBA map.
The SCUBA-2 survey of the local molecular cloud population will
provide a homogeneous catalogue of pre-stellar cores and protostars of
unprecedented size. While this has by itself intrinsic scientific
value, measurements of the kinematics of these cores and clusters of
cores will allow us to address a large number of fundamental
scientific problems in star formation, for the first time using
samples that are large enough to be statistically significant.
In typical star-forming molecular cloud cores, like that shown in
Figure 5, temperatures and densities are in the ranges 10-50 K and
10,000-100,000 particles per cubic centimetre. These are the
conditions under which the CO and isotopic CO lines in the 350 GHz
range are excited. The key goals of the HARP-B line observations are:
to search for and map any high velocity outflows present in the cores
to provide age estimates for the embedded objects; to measure the line
widths and velocity profiles in the cores and filaments to help
understand cloud support mechanisms and their evolution; to
characterize the nature of cloud turbulence in a wide range of
environments; to derive simple constraints on the column density and
CO depletion in these cores; and to generate a large sample of objects
for detailed follow-up with the eSMA and ALMA. These data will also
complement the wide-field survey data being obtained at
optical, near-IR and mid-IR wavelengths at the CFHT, UKIRT and with
FIGURE 5: A map of L 1448 in Perseus showing the CO outflows in red and blue
contours, superposed on to a SCUBA submillimetre continuum map of the region
(Hatchell et al., priv. communication) |
Attempts to characterise the magnetic field in star-forming regions are
driven by the need to understand its significance to the formation of
cloud structure and/or to the regulation of cloud
core collapse. These factors are related to star formation rates and molecular
cloud lifetimes, issues for which there is substantial debate in the
literature (Myers & Goodman 1988; Hartmann et al. 2001; Elmegreen
Measurements of polarized emission from dust are the most
effective means of probing the magnetic field within molecular clouds
and cores, since absorption polarimetry is limited to the periphery of
dense clouds and Zeeman splitting detections are relatively few
(Crutcher 1999). In contrast, polarized emission from dust is detected
from all objects on all scales observed (e.g. Matthews et al. 2001;
Crutcher et al. 2003) and from all compact sources, regardless of
evolutionary epoch (Ward-Thompson et al. 2000; Matthews & Wilson
2002). Sensitivity limitations have generally restricted observations
to several dozen bright (i.e., > 1 Jy), compact objects (e.g. Figure
6). The key goals of the polarimetric mapping proposed as part of the
Gould's Belt Legacy Survey are therefore: to obtain maps of
polarization position angle and fractional polarization in a
statistically meaningful sample of cores; to characterize the evidence
for and the relevance of the field and turbulence (in conjunction with
HARP-B observations) in cores and their surrounding environments; to
test the predictions of the standard low-mass star formation theory
(core, outflow, field geometry); and to generate a large sample of
cores suitable for follow-up with forthcoming single-dish polarimeters
FIGURE 6: These images show the importance of mapping the ambient
environment around cores and the advantage of high resolution. The
SCUBA Serpens map (Davis et al. 2000) shows that the field structure
can be more complex between the cores than their polarization patterns
indicate. The same is true in Barnard 1 (centre; Matthews & Wilson
2002). The NGC 2024 map at right shows that SCUBA observations (red)
of extended structure in Orion (Matthews, Fiege & Moriarty-Schieven
2002) reveal systematic variations missed in earlier lower resolution
maps (green; from Dotson et al. 2000). The Orion B map reveals how critical
resolution is to the effective mapping of magnetic field
The science questions which this survey will address directly are
of fundamental importance to star formation studies. What are
the relative timescales of each of the protostellar stages? How does
protostellar collapse proceed? What determines the stellar initial
mass function (IMF)? How does the environment influence protostar
formation? How do brown dwarfs form? What is the detailed spatial and
velocity structure of the molecular clouds in which star formation
occurs? What is the relative importance of magnetic fields and
turbulence in providing cloud support? By answering or constraining
these vital questions, the immediate impact of this survey will be
Area Coverage and Numbers of Targets Planned for the Survey
||Target 3 ||Area4
|5-yr plan9 |
| SCUBA-2||850 micron|| Av >1 ||562 sq. deg.
||10 mJy/beam || ||1/2 ||131 ||131|
| ||850 micron|| small clouds ||120 sq. deg.
||10 mJy/beam || ||1/2 ||19 || 19 |
| ||850 micron|| blank field ||10 sq. deg.
||10 mJy/beam || ||3 ||5 || 5 |
| ||450/850 micron||Av >3 ||107 sq. deg.
||12/3 mJy/beam || ||1/2 ||125 || 257 |
| HARP-B ||12CO ||1000 cores ||1000 x 2'x2' ||0.3K
||1.0 ||3 ||27 ||30|
| ||12CO ||10 clouds ||10 x 30'x10' ||0.3K
||1.0 ||3 ||19 ||22|
| HARP-B ||C18O(13CO) ||363 cores ||350 x 2'x2'
||0.3K (0.25K) ||0.1 ||1/2 ||8 ||114|
| ||C18O(13CO) ||10 clouds ||10 x 30'x10'
||0.3K (0.25K) ||0.1 ||1/2 ||92 ||236|
| POL-2 ||850 micron ||cores ||100 x FOV
|| 1 mJy/beam || ||2/3 ||50 || 126|
| ||850 micron ||clouds ||10 x 30'x10'
||1 mJy/beam || ||2/3 ||32 ||80|
|Total || || || ||
|| || ||508 ||1020|
1Instrument to be used.
2Continuum wavelength or CO isotope.
3SCUBA-2 target regions will be defined by extinction maps; only the higher-extinction regions
will be mapped at 450 microns.
4Approximate area to be mapped in each tracer.
5Sensitivity limit of each map.
6Spectral resolution of the CO maps.
7Weather conditions needed for each survey component, 1 being the best.
8Time dedicated to each survey component in the first two years.
9Approximate time required to complete each survey.
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Crutcher, R.M. 1999, ApJ, 520, 706
Davis, C.J. et al. 2000, ApJ, 530, 115
Dobashi, K. et al. 2005, PASJ, 57, 1
Elmegreen, B.G. 2000,MNRAS, 311, 5
Hartmann, L., Ballesteros-Paredes, J., & Bergin, E.A. 2001, ApJ, 562, 852
Hatchell, J. et al. 2005, A&A, 440, 151
Johnstone, D., Di Francesco, J. & Kirk J. 2004, ApJ, 611, L45
Kirk, H., Johnstone, D., Di Francesco, J. 2006, in prep.
Matthews, B.C., & Wilson, C.D., 2002, ApJ, 574, 822
Matthews, B.C., Wilson, C.D., & Fiege, J.D. 2001, ApJ, 562, 400
Matthews, B.C., Fiege, J.D., & Moriarty-Schieven, G.H., 2002, ApJ, 569, 304
Myers, P.C., & Goodman, A.A. 1988, ApJ, 326, 27
Ridge, N.A. et al. 2005, in prep.
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Authors: Jane Buckle (Cambridge), James Di Francesco
(NRC-HIA), Jane Greaves (St Andrews), Jennifer Hatchell (Exeter),
Michiel Hogerheijde (Leiden), Doug Johnstone (NRC-HIA), Brenda
Matthews (NRC-HIA), Dave Nutter (Cardiff), John Richer (Cambridge),
Derek Ward-Thompson (Cardiff)
Pierre Bastien, Chris Brunt, Jane Buckle, Harold Butner, Brad Cavanagh,
Chrysostomou, Rachel Curran, Emily Curtis, Chris Davis, Bill Dent, James
Di Francesco, Michel Fich, Jason Fiege,
Laura Fissel, Per Friberg, Rachel Friesen, Gary Fuller, Sarah Graves, Jane
Greaves, Andrew Gosling, Jennifer Hatchell, Michiel Hogerheijde, Martin
Houde, Ray Jayawardhana, Doug Johnstone, Gilles Joncas, Helen Kirk, Jason
Kirk, Lewis Knee, Brenda Matthews, Henry Matthews, Chris Matzner, Gerald
Moriarty-Schieven, Dave Nutter,
Russell Redman, Robert Simpson, Michael Reid, John Richer, Marco Spaans,
Ewine Van Dishoeck, Serena Viti, Derek Ward-Thompson, Bernd Weferling,
Glenn White, Ant Whitworth, Jan Wouterloot, Jeremy Yates, Ming Zhu
A restricted wiki page is available for team members at: http://wiki.astro.ex.ac.uk/bin/view/JCMTGouldBelt/WebHome.