DAAD-Projekt C

»The Faintest Active Galactic Nuclei – Constraining Black Hole Growth Across Cosmic Time«

Prof. Dr. Lutz Wisotzki (AIP, advisor) and Prof. Dr. Philipp Richter (UP, co-advisor)

Background: While it is now established that all large galaxies harbour supermassive black holes (BHs) in their centres, we still lack a proper understanding of their origin. The discovery of bright quasars at high redshifts proves the existence of very massive BHs already in the very young universe, even before galaxies were fully formed. But our picture of BH demographics is substantially incomplete: Low-mass BHs probably also exist at all redshifts, but are the hardest to detect as they leave the least observable imprints. Arguably the most sensitive approach to identify low-mass BH candidates at high redshifts is by searching for faint Active Galactic Nuclei (AGN) in deep surveys. The advent of new astronomical instrumentation at large telescopes makes this now possible.

Aims: We want to build a sample of type 1 AGN with very low bolometric luminosities, especially at redshifts z > 3, and study the properties of the corresponding black holes. We will estimate black hole masses from optical spectroscopy, infer the mass and Eddington ratio distribution functions, and constrain the activity duty cycle of the lowest mass black holes in the young universe. As an additional (mostly educational) assignment, the doctoral student will also be involved into a team effort to perform the spectroscopic identification of ultra-faint AGN in nearby galaxies from the CALIFA survey.

Methods: The data for this project will be obtained with the revolutionary MUSE instrument [1] which will be installed in the spring of 2014 at the ESO Very Large Telescope in Chile. A major part of the Guaranteed Observing Time (GTO, coordinated by the advisor of this project) will be dedicated to a survey for faint emission line objects that reaches an order of magnitude deeper than existing searches with narrow-band filters. While the main objective of that survey is to study the formation of galaxies, the same data will provide a unique bonanza to search for weak AGN with broad emission lines. The student will have to develop criteria to isolate likely broad-line AGN from other galaxies, learn how to perform spectroscopic measurements of emission lines, and interpret the measurements in terms of BH demographics [2]. In the second assignment, the student will obtain complementary know-how about low-mass BHs in the local universe by participating in the spectroscopic classification of emission-line galaxies observed by the CALIFA project. CALIFA [3] is a legacy survey conducted since 2010 with the Potsdam-built PMAS instrument and comprises already more than 200 dark nights at the Calar Alto Observatory. In this assignment, the student will learn about analysis techniques and methods of optical spectroscopy, also with the idea of acquiring the know-how to explore large spectroscopic databases such as CALIFA.




  1. R. Bacon, M. Accardo, L. Adjali, et al., 2010: The MUSE Second-Generation VLT Instrument. In: Ground-Based and Airborne Instrumentation for Astronomy III, I.S. McLean, S.K. Ramsay, H. Takami (eds.), Proceedings of the SPIE, 7735, 7
  2. A. Schulze, L. Wisotzki, 2010: Low Redshift AGN in the Hamburg/ESO Survey. II. The Active Black Hole Mass Function and the Distribution Function of Eddington Ratios. Astronomy and Astrophysics, 516, 87
  3. S.F. Sanchez, R.C. Kennicutt, A. Gil de Paz, et al., 2012: CALIFA, the Calar Alto Legacy Integral Field Area Survey. I. Survey Presentation. Astronomy and Astrophysics, 538, 8