The Astrophysics group has a strong research
program studying star formation and the interstellar medium. Combining optical,
infrared, millimetre and radio telescopes the group is undertaking a diverse range
of projects exploring the environment in which star formation occurs in our Galaxy.
The group makes major use of the Mopra
millimetre wave telescope, at Siding Spring Observatory and the NANTEN2 telescope at the 5,000m Atacom plateau of Chile.
Research programs centre around both the
study of individual sources and the development of new facilities for furthering
Polyaromatic Hydrocarbon (PAH) emission at 3.3µm in the NGC 6334 star
forming complex, imaged with the SPIREX telescope at the South Pole
Infrared (left, 2MASS) and Optical (right, AAO) images
of Eta Carina and the Keyhole Nebula.
The principal research
- The evolutionary sequence to massive star formation
- The environment of star forming complexes
and outflows from young stellar objects
The various stages of the
star formation process, from initial collapse of a cloud core, through the formation
of a disk and outflow, to the emergence of a young star from its natal cloud,
are now beginning to be defined from an observational basis. Massive star formation,
in particular, is a spectacular event which can be seen across the Galaxy. Through
conducting an investigation of 6.6GHz methanol maser emission associated with
the ultra-compact HII region phase of massive star formation (when an ionized
bubble forms around the young star), our work showed that the masers actually
predate the UCHII region phase, and are a signpost to a hitherto unknown stage
of the formation process. We have postulated they originate in 'Hot Molecular
Cores', and mark the very earliest phase of the massive star forming process.
Our work has opened up new avenues of investigation into star formation, including
searching for (and discovering!) protostellar embedded sources.
the massive stars form they have a dramatic effect on their environment, bombarding
their natal molecular clouds with winds and intense radiation fields. This both
lights up the environment, and feeds back into regulating the rate of star formation
in the cloud. We have been studying the evolution of star forming complexes, such
as NGC 6334 in its early stages, and the Keyhole Nebula in Carina which has nearly
finished shredding its natal cloud.
Star formation also produces collimated
outflows. This is particularly evident in low mass star formation, where the confusing
effects of winds and intense radiation fields are absent. These flows also stir
up the clouds and drive turbulence within them, shock-heating the ambient gas
they interact with. We are studying these mechanisms, in particular the interaction
of the outflows with the clouds.
Excitation of Molecular Clouds
The main research areas here are:
This research involves studying the excitation of the hydrogen molecule
by interstellar shock waves and by UV-fluorescence. Such activity takes place
in star forming regions, including photodissociation regions (PDRs), the surfaces
of molecular clouds heated by UV radiation. This work involves a broad-ranging
observing programme applying a combination of imaging, spectroscopic and polarimetric
techniques to study the hot gas in molecular clouds. While it has concentrated
on the near-IR spectrum from the v=1 vibrational level of H2, it has
developed to the study of emission from highly-excited levels of the molecule.
Such lines allow us to distinguish between the relative merits of competing models
for the emission, which diverge in their predictions for the population of higher
energy levels. It involved, for instance, the first measurements of the molecular
hydrogen emission in the optical CCD regime. Other aspects of this research include
observing the H2 line profiles at high spatial resolution, to probe
the structure of bow shocks, and comparing the distribution of different emission
lines in a source. An example here includes the spectacular discovery of a plethora
of bullets (from an explosion in the core of the Orion Nebula).
Debris from an interstellar explosion, imaged with the IRIS on the AAT
The Interaction of Supernova Remnants with Molecular Clouds
|Supernovae must commonly explode within or
nearby to their natal molecular clouds. Their expanding blast wave interacts and
overruns these clouds. Yet relatively few such examples are known. Such a SNR
looks different to 'conventional' remnants, with the bulk of the emission irradiated
in the IR rather than the optical, through molecular hydrogen and atomic fine-structure
lines. These SNRs provide a laboratory to examine the interaction of a shock wave
with molecular gas, uncontaminated by the activity associated with star forming
regions where such events are usually observed. Our work has included studying
these interactions in several Galactic and LMC remnants, undertaking wide-field
near-IR imaging of the molecular hydrogen and ionized iron emission, and measuring
their total energy budget. The recent suggestion that 1720 MHz OH maser emission
may be a signpost to this activity has lead to a new program to search for (and
find!), associated shocked molecular hydrogen line emission.||
Infrared image of the ICC443 Supernova Remnant (red-shocked molecular hydrogen,
blue-shocked iron; 2MASS).
The Centre of the Galaxy
|The hostile environment of the Galactic Centre
is an unlikely place to find both molecular clouds and star formation, but it
is in fact home to both. Massive star formation is occurring within the central
2 parsecs of the Galaxy, and in a number of clusters within the inner 100 parsecs.
These stars form a population I core to our Galaxy, whose (unobserved) lower mass
members may provide the bulk of the mass within the central parsec? Or it may
lie in a million solar mass black hole? Our work involves, particularly, studying
the stellar population in these young clusters, to determine the nature of the
massive stars that are forming from their near-IR emission spectrum. A recent
development has been imaging the molecular hydrogen emission from the circumnuclear
disk and in the Sgr A East supernova remnant to understand its excitation and
dynamics. This combines both HST/NICMOS and the AAT/UNSWIRF, the former to provide
exquisite spatial resolution, the later to remove the strong continuum emission
from the stars and to measure the gas velocities. We are currently undertaking a project to map the Central Molecular Zone, the inner 300pc of our Galaxy, in a variety of organic molecules. The CMZ is the repository of 10% of our Galaxy's molecular gas. The project makes extensive use of both the Mopra and NANTEN2 telescopes.
Infrared (IRIS, AAT) view of the Centre of the Galaxy