Starformation and Astrochemistry
Massive stars have a strong influence on the appearance of galaxies: with their strong outflows during their formation, their winds and UV radiation and, at the end of their lifes, powerful supernova explosions. In spite of their importance, much less is known about their process of formation than for their lower mass, sun-like siblings.
Using teleccopes operating at a large range of wavelenghts (e.g. at cm-wavelengths using Effelsberg and at submm-wavelenghts using APEX, Herschel, SOFIA) many aspects of star formation are studied, in particular with large scale spatial surveys to find and characterize star forming regions in a variety of evolutionary stages and with molecule line surveys to determine their physical and chemical conditions.
Galactic Center Research
Because of the proximity to the center of our Galaxy, the molecular clouds in the Galactic Centre have different characteristics than the molecular cloud in the disk, such as high kinetic temperatures, large linewidth, high cosmic ray ionization rates, etc. They are influenced by large potential gradient and are exposed to very energetic activities that are unique in the Galaxy, which influence the physic and the chemistry of them. The study of the Galactic center offers us an excellent opportunity to explore in detail the chemical and physical processes present in the center of the galaxies.
The Milky Way is a barred spiral galaxy, as seen from observations of CO and HI gas, and star counts. However, our location in the Galaxy makes it difficult to determine the number and positions of spiral arms, the extent and orientation of the central bar, and the Galaxy's rotation curve. As a result, even the most fundamental parameters of the Milky Way, such as the distance to the Galactic center, R0, and the rotation speed, Î0, are still not known with high accuracy. These values are not only important for Galactic astronomy, but also for a wide range of different fields. In recent years, many large scale surveys have covered the Galactic Plane in all wave bands from radio to gamma rays. All of these surveys are two dimensional, and using them to construct a three dimensional model of the Milky Way is not trivial, mainly due to large uncertainties in distance measurements. These uncertainties also affect the interpretation of these surveys, since most astrophysical quantities, such as linear size, mass, and luminosities, strongly depend on the distance to the object.
Late Stages of Stellar Evolution
At the end of their lives, stars go through a sequence of red giant phases accompanied by intense stellar mass loss. This results in atomic and molecular circumstellar envelopes enshrouding the central asymptotic giant branch (AGB) stars and leading to bright infrared sources. Eventually the star becomes hot enough to ionize the envelope, starting the evolution of a planetary nebula (PN). Furthermore, the rapid transition stage between AGB and PN phase is crucial for our understanding of the properties of planetary nebula. Objects in this stage are called proto-planetary nebulae (PPNe) and are very rare.
Studies of the interstellar medium and the radio continuum provide key information about the physical and chemical processes which drive the evolution of galaxies. Observations in the sub-millimeter wavelength regime, as provided by APEX and Herschel, are in particular critical as they trace the cold gas reservoir - the material from which new generations of stars are born. The relations between the chemical and physical properties of the cold molecular gas and star formation are key research areas of our group.
In the coldest phase of the interstellar medium is mainly molecular. Observations of molecular emission lines and radiation from dust grains allow us to measure the gas kinematics, cooling balance and chemical composition of the molecular clouds.
The environment in which cold clouds reside largely affects their capabilities to form stars. Observations of nearby galaxies probe the full scale of conditions met in the local universe and therefore provide important clues to interpret the star formation and galaxy evolution in the early universe. [more]
The Early Universe
Over the past decade tremendous progress has been made in our understanding on galaxy evolution throughout the live time of the universe. Deep sub-millimeter observations are particularly important as they trace dust obscured star-forming galaxies which are often difficult to detect at other wavelength. Unlike observations at other wavelength, the dimming of sub-millimeter light due to the tremendous distances is compensated by increasing intrinsic intensities caused by the redshift and the shape of the spectrum of galaxies at this wavelengh. As such sub-millimeter intensities of distant galaxies remain roughly constant over a large redshift range.
In collaboration with researchers all over the word our group has been leading one of the largest sub-millimeter deep field surveys using LABOCA on APEX. The initial detection of dusty starforming high redshift galaxies in this and other survey allows us to study this endigmative objects in great detail at multi-wavelenght. Ongoing studies include follow up observations with the IRAM facilities, ALMA and many other world leading observatories. High spatial resolution imaging and spectroscopic observations at different wavelength allow us to charcterize these mega-starburst and to put them into the context of galaxy evolution over the Hubble time. Furthermore these distant objects allow us to test fundamental physical paradimes such as potential variations of the fundamental physical constants. [more]