Fields of Research

Lyman Alpha and UV Continuum-Emission

I am an observational astronomer currently doing PhD studies at the Department of Astronomy of the University of Stockholm under supervision of Matthew Hayes. My thesis is based on the still poorly understood role of Lyman Alpha Emitters (LAE) within the cosmological epoch of reionization, about only 0.4 to 1 billion (109) years after the Big Bang corresponding to a redshift of z=11 to z=6, respectively. In order to get a better understanding of observations at these high redshifts, I am using local counterparts of those high-z LAEs. Thereby, I rely on the so called “Lyman Alpha Reference Sample” (LARS), which was defined by Hayes et al. (2013) and consists of 14 galaxies up to a redshift of z=0.2. The advantage is that LARS galaxies can be studied in much more detail compared to LAEs at high-z. I aim to learn about the underlying physical conditions responsible for effective UV emission on a galactic scale. Morphological and kinematical aspects certainly play an important role as well as the overall atomic hydrogen content. However, since UV radiation is intimately linked to an ongoing process of star-formation, the molecular gas must play a major role too, because molecular hydrogen is the main ingredient – the fuel – for star formation.
Beside LARS, I am working on HST/COS data of Tololo 1247-232, which is the second known Lyman Continuum Emitter in the local universe to date. From its leakage, I am trying to learn about underlying physical properties leading to an effective UV emission shortward to the Lyman limit.

Star Formation and Molecular Gas in the Local Universe

During my master studies at the Department of Astrophysics of the University of Vienna, I was working within the collaboration of CALIFA, the Calar Alto Legacy Integral Field Area survey. The CALIFA sample consists of 600 local galaxies with redshifts ranging from z=0.005 to z=0.03. CALIFA has been designed to obtain maps of stellar populations, ages, metallicities, ionized gas distributions, gas excitation mechanisms, chemical abundances as well as kinematic properties from stellar and ionized gas components. However, a key piece for the complete understanding and interpretation of the nature and properties of star formation in the investigated sample is missing: the cold molecular gas reservoir, the fuel for star formation.
That missing key piece was subject to my master thesis, supervised by Dr. Helmut Dannerbauer and Prof. Bodo Ziegler. My thesis, entitled Census of the Molecular Gas in Nearby Galaxies Selected from the CALIFA Survey, can be understood as a preliminary study of the ultimate goal of obtaining interferometric CO maps with ALMA, PdBI and CARMA with matching spatial resolution of the optical IFU data of 2 arcsec (corresponding to a physical scale of 200-760 pc) to investigate molecular gas properties of local galaxies on a statistical basis.
Based on an extended literature and archival search for CO data, I was able to homogeniously calculate molecular gas masses of a subsample of CALIFA galaxies. For that purpose, a sophisticated aperture correction was applied to the data in order to get accurate and comparable results. Finally, I was able to set up the Kennicutt-Schmidt relation for CALIFA. Based on the findings, star formation efficiencies as well as gas depletion timescales could be derived and discussed. Furthermore, a detailed analysis of the molecular gas distribution within a local late-stage-merger, NGC2623, was performed. Thereby, CO J=1-0 data gained with the Submillimeter Array (SMA) was calibrated, reduced and interpreted. The so gained spatially resolved CO maps were compared to CALIFA’s maps of ionized gas. It was found, that a huge molecular clump with a size of approximately one kiloparsec, is currently fallen into the center of the galaxy, whereas at the same time the ionized gas is streaming outwards. These findings are in agreement with the late-stage-merger model of Iono et al. (2004) and thus a confirmation of that model.
Additionally, I have provided the CALIFA collaboration with a MySQL based database with many filtering and sorting mechanisms of all compiled multi-wavelength data including images and spectra.

Light Pollution Research

Up to now, astronomers have mainly been measuring the brightness of the night sky (in magnitudes/arcsec2) at dark sites, especially at modern mountain observatories, or at potential observatory sites as part of “site-testing”. Within the past few years, it has become evident that increasing night sky brightness and light pollution have far-reaching consequences for many branches of human life as well as wildlife. Therefore, it is desirable to measure and monitor the night sky brightness not only at remote mountaintop observatory locations, but also close to the centers of modern civilization, and to do so every night, in a reproducible way, with the aim of performing long-term studies (such as in climate research). Only in this way can the impact of night sky brightness on biological rhythms on animal behaviour, and human health be assessed.
For that reason, I am working together with Thomas Posch (Dept. of Astrophysics, Univ. of Vienna), Stefan Uttenthaler (Dept. of Astrophysics, Univ. of Vienna), Axel Schwope (Leibniz-Institut für Astrophysik Potsdam, Germany) and many other people on setting up so called Sky Quality Meters (SQMs) at as many locations as possible. So far, we were able to establish a small network of SQMs with stations in Vienna (AT), Lower Austria (AT), Linz (AT), Potsdam (DE) and soon Stockholm (SE). The measurements are visualized in real-time and accessible through our Light Pollution Website.
Furthermore, we have already performed an analysis of our first year data gained in Vienna and our two-year dataset gained at Potsdam. Our results can be found in two articles published in the Journal of Quantitative Spectroscopy and Radiative Transfer (JQSRT):

Additionally, on behalf of the Department of Environmental Protection of the State Government of Upper Austria, led by Ing. Heribert Kaineder, I was able to substantially contribute to creating a guideline for the Upper Austrian districts on how public lighting ideally should be used in the future in order to minimize light pollution. The created brochure entitled “LEITFADEN Besseres Licht – Alternativen zum Lichtsmog” (only in German) gives an introduction into the topic as well as practical guidance when installing outdoor lightings.

Updated by Johannes on April 25, 2018.