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JPS
JCMT
Galactic Plane Survey
Summary
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The basic science goal of the JPS is to achieve a full census of
star-formation activity in the plane of the Galaxy observable from
JCMT, to a detected mass limit of around 40 solar masses at the far
edge of the Galaxy. Given this limit and the latitude range (equivalent
to the scale height of OB stars at ~3kpc), the specific science goals
are related to high-mass star formation and can be grouped under four
main headings:
- An Evolutionary Sequence for high-mass SF:
A complete sample of all embedded phases of high-mass young stellar
objects, in comparison to existing (and planned) IR-selected samples,
will allow a determination of a basic evolutionary sequence. In
particular, the numbers and distribution of objects detected in the
submm continuum but not in the IR will establish the length of the
poorly understood earliest evolutionary phases and the extent to which
triggering and clustering are necessary conditions for high-mass star
formation.
- Triggering and the star-forming content of molecular clouds:
Measurements of the potential star forming content of molecular clouds,
in the form of dense and potentially bound structures will allow us to
measure the natural variation of this 'star-formation' efficiency and
of the mass function in dense cores in different environments. We will
be able to quantify the effects of triggering interactions (compression
due to OB star winds, expanding HII regions and SNe) on the production
and mass distribution of dense structures, a first step towards a
quantitative understanding of the effects of feedback on star
formation. In addition, we will be able to test models of star
formation in a turbulent environment.
- Cold Dark Clouds and the formation of molecular clouds:
In order to understand star formation we need to determine the process
that produces the molecular clouds in which stars form. Cold Dark
Clouds (CDCs) contain both atomic and molecular gas and have densities
and temperatures that bridge the gap between the ambient atomic ISM and
cold, dense molecular clouds. Many have cold HI absorption without CO
emission but structures similar to molecular clouds. CDCs may therefore
be sites of formation of molecular clouds out of the turbulent neutral
medium. SCUBA observations will provide estimates of total gas columns
and hence constrain the atomic-to-molecular ratios in these objects.
Using 450/850 ratios and the FTS data, the JPS will also show how dust
properties, as manifested in the thermal balance and emissivity index
in the submm continuum, vary between and within CDCs.
- Galactic Structure:
The location of dense, star-forming structures relative to sites of
recent high-mass star formation traced by HII regions (e.g. from the
CORNISH VLA survey), OB clusters traced by UKIDSS and Spitzer, and the
far-IR traced Massive Young Stellar Objects will show the relationship
between two or three generations of high-mass SF yielding a structural
picture of star formation in the Galaxy, how it relates to Galactic
spiral structure as understood from, e.g. HI studies, and the
dependence on environment, especially with respect to the difference in
feedback rates in the inner and outer Galaxy.
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The shaded region is the area covered by SCUBA at 850 µm.
Green contours are integrated 12CO intensity from FCRAO. The circles
represent dense cores identified in the 850 µm data (sizes
proportional to their mass). Red circles indicate cores with evidence
of star formation while blue circles indicate cores without.
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The 2-year programme
The programme has been awarded, in its first two years, 334 hours
within weather band 2 with a target of reaching a sensitivity of 4 mJy
per beam at 850 µm. It aims to survey, at both 850 and 450
µm, the following areas:
- +10 < l (degrees) < +65; -1 < b (degrees) < +1
- +102.5 < l (degrees) < +141.5; -1 < b (degrees) < +1
There are 5- hours of FTS time also allocated to this project to help calibrate the 850/450 spectral index measurements.
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