The
Mopra Galactic Plane CO Survey – the formation of molecular
clouds
 This
site provides information about the molecular gas survey of the
southern galactic plane being conducted with the Mopra millimetre-wave
telescope in Coonabarabran, New South Wales, Australia. The survey
is designed to map the distribution and dynamics of the carbon
monoxide molecule (CO) along a 35 degree sector of the Galactic
Plane, from l=305°-340°. The principal scientific
motivation is to understand how molecular clouds are formed in
space. The data will be combined with similar survey data collected
on the sub-millimetre neutral carbon line (C) with the Nanten2
telescope in Chile, and the terahertz ionized carbon line (C+)
from the balloon-borne Stratospheric Terahertz Observatory (STO)
in Antarctica. With these surveys we will be able to build a picture
of the distribution and motion of the principal forms of carbon
in the interstellar medium. Taken together, these three species
can provide us with a picture of the molecular medium of our our
Galaxy.
With
the data we aim to answer a longstanding question: how do molecular
clouds form in the interstellar medium? This process plays a key,
but so far poorly understood, role in the life cycle of our Galaxy,
as it is from these molecular clouds that stars will be born.
To
understand molecular cloud formation we must first find all of
the molecular gas. An important, but unseen component, is the “dark” gas. Lacking the primary tracers found
in atomic gas (hydrogen atoms) and fully-developed molecular clouds
(carbon monoxide), this “dark” gas can be seen primarily
via the emission from atoms of neutral and singly-ionized carbon.
Interestingly,
this dark gas may also be associated with the emission of gamma
rays, produced when cosmic ray particles interact with gas nuclei
in the interstellar medium. Currently we cannot reconcile the distribution
measured for the gas using conventional tracers with that for the
gamma rays in many sources. This work will test the hypothesis
that the difference between these results arises from the presence
of dark gas.
To
address these questions we need to map the atomic and molecular
gas across a spiral arm of our Galaxy, thus determining the distribution
and dynamics of all the gas in all its states – including the dark component. We
will use three telescopes that our research team have developed,
in Australia, Chile and Antarctica, to trace the element carbon
in molecular, neutral and ionized gas. These novel telescopes are
able to look through hard-to-see windows in the atmosphere to measure
these spectral diagnostics. Together, they make it possible to
trace carbon in these forms (and hence all of the gas) over large
areas of sky, and with sufficient spatial and spectral resolution
to isolate individual emitting gas clouds and to determine their
motions through the Galaxy.
In
the pages linked below we provide further information on this program
as follows:
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