My professional tasks and achievements
Coordinating the International Research School for Astronomy and Astrophysics (2015 - )The International Max Planck Research School (IMPRS) for Astronomy and Astrophysics is a highly competitive-entry graduate program leading to a PhD degree in Astrophysics. The school is run in cooperation with the University of Bonn and University of Cologne. Its speaker is Prof. A. Zensus. My task is to manage and coordinate the activities of this IMPRS. I am also affiliated to the faculty of Mathematics and Science of the University of Bonn as a "Privatdozent" (Adjunct Lecturer).
Commissioning ALMA 2008 - 2013When I arrived in 2008 as a member of the ALMA science team, there were just three antennas at the ALMA base camp. Since they stillhad no radio receivers, we verified the pointing of the antennas using a small optical telescope. In mm astronomy, we have no guide stars (infact, we can observe during the day and even through clouds). Therefore the ALMA antennas are designed to blindly point with an accuracy of 2"to any point in the sky, even if it gets very cold and windy. It was quite some effort to get there. Other examples of our challenges arethat the relative positions of the antennas must be known within a few 10 micron, and that atmospheric fluctuations must be cancelled out byonline sampling the fluctuations of water vapor.
Several important milestones mark the last years: The first radiolight; the first correlated signals between two antennas (we call them "fringes"); the first antennas going up on one of those gigantictransporters from the basecamp at 3000m where the antennas are assembled up to the operations site at 5000m. We were proud of ourfirst fringes, but we were delighted and stunned by the first images. More and more antennas went up until ALMA went into its operationsphase in September 2012; and now several scientific publications are released every month. I described this fascinating process to reachfirst images in an articel for the JAO newsletter.
Besides doing commissioning work for ALMA I enjoyed much my job as co-editor of the ALMA Science Newsletter, where we documented the process made during the construction phase of ALMA.
Station Manager of the IRAM 30-m Telescope (1999-2008)The IRAM 30-m telescope is the world foremost single dish mm-wave telescope. It is located near Granada (Southern Spain) at an altitude of nearly 3000m. As the station manager, I was responsible for a staff of 30 and a yearly budget of 2M€. There were about 200 scientific visitors every year at this highly oversubscribed facility. We not only constantly improved the receivers and antenna but also changed our mode of operations from a pure visitors mode to a mode of flexible observing. I am happy and also a bit proud that this worked out in an international institution where stakeholders from three different countries are eager to get their share of science time. I am also proud that we could organise this new mode without increasing our support staff. Flexible observing and a much improved antenna makes it possible that the 30-m telescope now is able to produce results at wavelengths of <1mm.
I was also successful to get national funding in order to foster institutional collaborations in the fields of galaxy evolution and astronomical databases with the Instituo de Astroficia de Andalucia (Granada) and the Instituto de la Estructura de la Materia (Madrid). More important than the funding we obtained was the strengthening of our scientific bonds to Spanish instituions other than our stakeholders.
Science and Commissioning at the SMT on Mt. Graham (Arizona) (1995-1999)Between 1995 and 1999 I was as a Heisenberg Fellow at Steward Observatory, which at that time commissioned the SMT a 10m sub-mm telescope on Mt. Graham. In fact the first day I arrived at the observatory, I was asked whether I would like to help cleaning the surface. Of course I agreed. In fact the telescope was brand new and the high accuracy surface was still covered with a plastic film. I climbed into the dish, equipped with a protective gear and removed the plastic cover with some solvent. Despite being February, it got very hot there under the Arizona sun. Despite having started my American career literally as a dishwasher I did not become a millionaire ;-). Instead I had ample time for scientific projects with the 12m radiotelescope, the SMT and other radiotelescopes. I was also part of the steering committee who managed the commissioning of that telescopes. As everybody knows, Mount Graham went through some difficult times due to ethnical groups and ecologists wanting to stop the project. Also, it turned out that the weather was not as good as expected from the previous site testings. What I certainly learned from this experience is how important a good public outreach is and also how crucial it is to be aware of the different cultures.
My scientific experience and achievements
Physical conditions in the Galactic and extragalactic interstellar mediumStars like our sun are still forming from clouds of molecular hydrogen, dust and other molecules and atoms. When a massive star is forming by gravitation collapse in such clouds, the gas might be heated to temperatures exceeding 100 K, which for the molecular interstellar medium is considered as hot. When I started my PhD thesis, only the Orion and Sagittarius B2 hot cores were known. I was not only able to identify a significantly larger number of hot cores by using ammonia NH3 cm line emission and absorption as temperature and density tracer, we could also show that a large and extended region in our Galactic center has temperatures larger than 100K. The heating mechanisms must be different: while hot cores are heated via stars that warm up dust, which in turn heats the gas, in the GC our explanation is that turbulent energy is converted to heat. For the paper that led to my PhD thesis, I was awarded the Otto-Hahn-Medal of the Max-Planck-Society.
In 1994, I was awarded the Bennigsen Foerder Prize of the land Northrhine Westfalia, which came with 150000 DM. In collaboration with Leo Bronfman from the Universidad de Chile we refurbished the 1.2m Southern Columbia telescope on Cerro Tololo to map the central few 100pc of the Milky Way in the emission line of C18O, a rare isotope of CO, which is 500 times rarer than normal CO. The objective was to check whether the assumption that normal CO, although it is optically thick, is a good quantitative tracer of the H2 mass. Our main finding was that CO overestimates the gas masses in the central region of our Galaxy by a factor of >5. Our explanation was that in the center of the Milky way, CO is no longer virialized since it experiences the gravitational potential of the stars in the Milky Way center and also collisions with other clouds. In addition the assumption that normal CO is always optically thick may not be valid in the Galactic center.
Using the IRAM 30m telescope, we could show that also in the centers of external galaxies such as NGC 253, CO alone overestimates the H2 mass. In the meanwhile this is generally accepted. During my career, we used molecular line emission from NH3, CS, CH3CCH and other molecules to estimate the densities and kinetic tempertaures in the central regions of nearby galaxies. The physical conditions in these extended regions resemble more a hot core than quiescent molecular clouds, and are with this respect similar to our own Galactic center. I summarized the comparative studies of the physical properties of the Milky Way and other nearby galaxies in a review article and in my Habilitation Thesis (in Germany a habilitation earns you the rights and duties of a Privatdozent, an unpaid assistant professor).
Interstellar ChemistryThe interstellar medium of hot cores is surprisingly rich in more or less complex molecules. In a number of papers we confirmed that several moleules such as ammonia, water and methanol (CH3OH) are much richer in their deuterated substitutions (e.g. CH3OD) than expected from gas phase chemistry. The scenario that explains this best is htat the molecules are enriched in a cold environment and that these molecules froze out on dust grains. When the newly formed stars heat the gas to become a hot core, the deuterated molecules evaporate and can be observed with mm-wave telescopes. We could also detect deuterated molecules for the first time outside the galaxy.
When observing nearby galaxies, we realized that the gas in many nearby is not only as hot and dense as hot cores but surprisingly rich in its chemistry. Using the 30-m telescope we detected a large fraction ofextragalactic molecules for the first time. Among those are molecules as complex as methanol (CH3OH), methyl cyanide (CH3CN) or methyl acetylene (CH3CCH) and also ions such as N2H+ and tracers of hot gas like SiO. When broad band receivers became available my students and I took advantage and observed the first unbiased spectral line sweeps to several kinds of galaxies such as galaxies in an early (NGC253) or late (M82) stage of star formation, or those containing an AGN (NGC1068). We completed these studies with chemical studies of differnet regions of our Milky Way center. We observed large differences in their chemical composition and could show that these are due to differnt environmental conditions such as shocks or ionizing radiation. A large number of publications is based on these observations.