Projects and Collaborations
The interest and work of our group divides into two broad science areas: the evolution of galaxies, and the observation of galaxy clusters through the Sunyaev-Zel'dovich (SZ) effect. Furthermore, we support the ALMA operations and its users through our ALMA Regional Center (ARC) node at Bonn/Cologne, and we participate in the construction of the CCAT-prime submillimeter telescope.
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CCAT / FYST
The centerpiece of the Cerro Chajnantor Atacama Telescope (CCAT) Observatory is the Fred Young Submillimeter Telescope (FYST), a 6-meter telescope designed for observations at submillimeter to millimeter wavelengths. It is located at an exceptional 5,600-meter site on Cerro Chajnantor in the Chilean Atacama Desert. FYST’s innovative optical design enables high-throughput, wide-field observations, allowing for rapid and efficient sky mapping. Its precision surface and superb location provide routine access to the 350-micron observing window.
Designed and built by CPI Vertex Antennentechnik GmbH, FYST was recently transported from its construction site in Germany to Chile and is now deployed at its final site. First light is expected in late 2026.
The University of Bonn is a partner in the CCAT Collaboration, which is responsible for construction of the telescope, instrument development, observatory operations, data analysis, and scientific exploitation. The Millimeter/Sub-Millimeter Astronomy Team at the Argelander-Institut für Astronomie supports both the scientific and technical aspects of the project. The groups of Profs. Bigiel and Porciani also support the science preparation of CCAT.
Contact: Prof. Bertoldi, CCAT Observatory website or here from our German perspective.
Galaxy evolution: A3COSMOS
A major focus of modern astrophysics is to understand how galaxies form, grow, and eventually cease to form stars. These evolutionary phases — and the transitions between them — are governed by a galaxy’s ability to sustain star formation.
With the A³COSMOS project, we study the physical properties and star formation activity of distant, high-redshift galaxies through their emission at (sub)millimetre wavelengths observed with the ALMA telescope. A³COSMOS compiles and uniformly processes all ALMA data available in the two major extragalactic fields, COSMOS and GOODS-South, covering more than 1300 arcmin² of sky and expanding continuously across the full ALMA bandwidth.
This homogeneous data set enables the construction of large, statistically robust samples of hundreds to thousands of galaxies, allowing us to trace their star formation histories and evolution across cosmic time. The resulting A³COSMOS database is made publicly available to the community.
Contact: Sylvia Adscheid, Benjamin Magnelli (CEA Paris-Saclay), Prof. Bertoldi
Collaborators: Daizhong Liu (Nanjing, China), Eva Schinnerer (MPIA, Heidelberg).
SZ Effect and Cosmology
Our research is centered on the study of the Sunyaev-Zeldovich (SZ) effect from galaxy clusters, which is a tiny chang of the intensity of the cosmic microwave background (CMB) radiation, caused by inverse Compton scattering off the energetic electrons in the intracluster plasma (arXiv:1903.04944). The SZ effect is a powerful tool in the study of galaxy cluster astrophysics and cosmology, providing information on topics as divers as the accelerated expansion of the universe and cosmic ray composition within AGN jets.
For over one decade we have been involved in the APEX-SZ cluster survey, using one of the world's first multi-pixel TES bolometer cameras, mounted on the APEX telescope in Chile. Our research has moved onto multi-wavelength follow-up of galaxy clusters, particularly in X-rays and at radio wavelengths, the analysis of all-sky data from the Planck satellite, SZ spectral measurements and the preparation for future multi-wavelength CMB/SZ surveys.
Currently our activities are focused on CCAT/FYST, which will undertake one of the most sensitive and most wide-spectrum surveys of galaxy clusters. This survey will start collecting data in 2026, and our team is involved in all relevant aspects of scientific and instrumental planning.
Contact: Dr. Kaustuv Basu.
Hydrogen recombination lines
Background: When studying the structure and evolution of distant galaxies, the total star formation rate (SFR) of a given galaxy is an important observable. It is related to the gas, dust, and stellar mass content of a galaxy, and is strongly related to the UV radiation field, which affects the physical and chemical state of the star-forming interstellar gas. The SFR can be inferred from several observational tracers, such as UV emission (from massive stars), far-infrared (FIR) emission (from dust heated by massive stars), radio synchrotron emission (from relativistic electrons accelerated in supernovae), or hydrogen recombination line emission in the ionized gas around massive stars, the so-called HII regions.
Aproach: A promising SFR tracer that has not yet been extensively studied for distant galaxies is the mm-wavelength hydrogen recombination line (mm-RL) emission. On the theory side we have been investigating how the physical conditions in HII regions affect the amplification and attenuation of mm-RL emission. Observationally we harvest the ALMA data archive to assemble mm-RL detections towards nearby (within a few hundred Mpc) star-forming galaxies. We compare the implied SFR of these galaxies when derived from the mm-RL emission and from their FIR emission, and find a linear correlation that is consistent with measurements of individual massive star-forming regions in our Milky Way galaxy, stretching over eight orders of magnitude. We find that several sources show mm-RL emission suffering from maser amplification, and that maser amplification cannot be ruled out even for galactic sources. Our aim is to assess the quality of mm-RL emission as a reliable SFR tracer.
Contact: Prof. Bertoldi, Dr. Toma Badescu
Line Intensity Mapping
Understanding how the first stars formed within the first generations of galaxies is a central goal in modern astrophysics. At high redshifts, most galaxies are too faint to be detected individually, so we use line intensity mapping (LIM) , a technique that measures the cumulative emission from many faint galaxies without resolving them. By capturing this emission across both the sky and frequency, LIM provides a three-dimensional view of large volumes of the Universe, allowing us to trace star-formation activity through spectral lines such as [CII] and CO.
Our work focuses on building realistic models of the LIM signal that connect line emission to star formation in early galaxies and will guide the interpretation of upcoming observations. Using cosmological simulations such as IllustrisTNG, we generate realistic mock maps to forecast the expected signal for instruments like the Fred Young Submillimeter Telescope (FYST/CCAT).
A major challenge for LIM is contamination from low-redshift foregrounds, especially CO emission. We design and evaluate foreground removal methods to isolate the high-redshift [CII] signal. In parallel, we apply our analysis techniques to real ALMA data to test and validate these methods on existing observations.
Contact: Dr. Christos Karoumpis
Collaborators: Prof. Bertoldi, Dr. Benjamin Magnelli (CEA Saclay), Prof. D. Riechers (U. zu Köln)
Galaxy evolution: the CCAT GalEvo project
A significant portion of the optical light from newly formed stars in the universe is absorbed by dust and re-emitted at infrared and submillimetre wavelengths. Observing distant galaxies on the mm and submm domain can shed light on how the universe assembled its galaxies and how they evolved over cosmic time. Using state-of-the-art observations from FYST with unprecedented depth and spatial coverage, we can trace the star formation history of the universe using comprehensive samples of hundreds of thousands of galaxies out to the highest redshifts. We combine multi-wavelength ancillary data with novel statistical and machine learning methods to identify, characterize and model the underlying dusty galaxy population.
Contact: Doctoral student Andrea Guerrero, Prof. Frank Bertoldi.
Collaborators: Dr. Benjamin Magnelli (CEA Saclay), Prof. D. Riechers (U. zu Köln)
