Molecular Gas and Star Formation in the Galactic Center Region

The Galactic Center is obviously the most nearby core of a galaxy. We conducted a
high-resolution, interferometric, wide-field survey of ammonia in this region with the
Australia Telescope Compact Array. Due to its molecular structure, ammonia can be
used as a thermometer and one of results comprise a temperature map of the dense
molecular gas between Sgr A*, the black hole in the center of the Milky Way, and Sgr
B2, one of the most prominent starbusts, at a resolution of ~1pc. our deep survey
also lets us to derive the properties of thousands of individual molecular clouds. This
provides comprehensive statistics of cloud sizes, densities, masses, temperatures,
and pressures. In addition, the survey provides a high-resolution map of the
continuum emission at 1.2cm wavelength.


The Interstellar Medium in the Magellanic System

The Magellanic Clouds are some of the most nearby galaxies. They are interacting
dwarf galaxies and exhibit low-metallicities and a high radiation field - conditions
which may resemble those of the distant Universe. We used both, the Mopra single
dish telescope and the Australia Telescope Compact Array to study the star
fromation conditions in these objects. Their proximity and their nearly face-on view
allow us to distinguish between different molecular cloud and star forming scenarios.
In addition, the properties of the dense gas can be determined and, hopefully, be
used to better understand star formation at the very early stages of galaxy evolution.



Molecular Gas and Star Formation in Starburst Galaxies and ULIRGS


With the Australia Telescope Compact Array we observed a sample of the most
prominent nearby southern starburst galaxies to detect the dense molecular gas. This
particular gas phase is the material from which stars ultimately form. Despite the very
strong ionizing radiation fields and the energetic impact of supernovae in starburst
galaxies, i.e., galaxies with an extremely high current star formation rate, the galaxies
still maintain their star formation activity over many tens or hundreds of Myr. It is
therefore important to know why the molecular gas is not destroyed, how it can form
in large quantities under such conditions, and why, eventually, starburst suddenly
stop. In particular we observed lines of ammonia, which are used to probe the
temperature of the dense gas. A second survey concentrates on the HCN/HNC ratio
which is sensitive to the radiation field in these extremely starforming objects.


 Triggering Star Formation and Stellar Feedback in Nearby Galaxies

Star formation can have a dramatic impact on the surrounding interstellar medium.
Young, massve stars are short-lived and dump massive amounts of mechanical
energy into their surroundings in the form of strong stellar winds and supernova
explosions. This influences the dynamics and energetics of the ISM and can be
observed, e.g., in the form of expanding supergiant shells, observable in the 21cm
line of neutral hydrogen (HI). This is of particular interest in dwarf galaxies, i.e.,
galaxies with a low gravitational potential. In fact, if the conditions are right, the
energetic input of star formation can remove part or all of the ISM in a galaxy, which
is an important factor for subsequent star formation and the metallicity enrichment of
the intergalactic medium. With the Very Large Array (VLA), we will be observing a
large sample of galaxies in a "Large Program" . This survey of ~70 galaxies is a
complementary to the ANGST project, the goal of which is to determine the spatially
resolved star formation history in a volume-limited sample of nearby galaxies with the
Hubble Space Telescope (HST). The combination of HST and VLA will be essential
to study the interplay of triggering of star formation and the stellar feedback of into
the ISM. The data will eventually be complemented by observations of molecular gas
with the Combined Array for Research  in Millimeter-wave Astronomy (CARMA).


Hot Gas in Dwarf Starburst Galaxies

As mentioned above, young massive stars dump massive amounts of energy into the
surroundijng ISM. A direct consequence is the thermalization of this energy which
heats up the gas to millions of degrees. This phase can be observed in X-ray
emission. For my thesis, I studied X-ray Chandra data of a sample of nearby dwarf
starburst galaxies. We determined the temperatures and the densities of this gas
phase, its energetics and the possible removal of ISM caused by it. It turns out that a
large envelope of less dense material may inhibit the total removal of gas, despite of
the low gravitational potential of their host galaxies. We also address the metallicity
distribution which arises from newly created elements in the supernovae, and
compare the X-ray emission to shock tracers such as Halpha emission and to the
cold atomica gas phase traced by HI. For one object, NGC3077, we were also able to
derive and compare the properties of different hot gas filled bubbles in the same
object.





For more information, please have a look at my list of publications, and feel free to
get in touch with me.