Coevolution

15 July 2016

Type: PhD position
Deadline: 12 September 2016

PhD position on triggering of high-accretion black holes

Formal description:

The Galaxies and Cosmology department of the Max Planck Institute for Astronomy (MPIA) in Heidelberg invites candidates to apply for a PhD position in the field of extragalactic astronomy to be carried out under the supervision of Dr. Knud Jahnke. The successful applicant will analyse two valuable datasets from the Hubble Space Telescope and the Very Large Telescope to investigate which mechanisms are triggering the growth of supermassive black holes in galaxies. The specific goal is to answer the question of whether galaxy mergers play a dominating role for black hole growth in galaxies at redshifts z=0.2 and z=2.

Research will take place at the very stimulating academic enviroment of the Max Planck Institute for Astronomy in Heidelberg, Germany. MPIA is one of the leading astronomical institutions in Europe, with currently ~40 full-time faculty, ~55 post-docs, and ~50 PhD students. The associated course program takes place within the framework of the International Max Planck Research School in Heidelberg, in collaboration with the University of Heidelberg. PhD students from MPIA succeed exceptionally well in the international job market. More information about research at MPIA can be found at http://www.mpia.de/en.

The starting date can be as early as 1 October 2016, but a later starting date up to mid-2017 is subject to negotiation. The successful candidate must have a MSc degree (or equivalent) by the starting date. The program is nominally for four years, with a contract likely in the form of 3 initial years with a one year extension. PhD students at MPIA are paid as civil servants with a salary based on TVöD (wage agreement for the public service), 50% E 13. Medical, social security and pension benefits are paid in accordance with the provisions of the civil service.

Applications should be sent by email to jobs16-06@mpia.de. A complete application includes a cover letter with preferred starting date, CV with list of publications, course record including grades from undergraduate and Master's courses (translated into english, if necessary), a summary of the Master's thesis, and a brief (1 page) statement of research interests and experience. Two letters of recommendation from scientists familiar with the applicant's work or studies should be sent to the same address. Incomplete applications can not be considered.

The Max Planck Society is an equal opportunity employer. Applications from women, disabled people, and minority groups are particularly welcome. The MPIA supports its employees in their search for suitable child care.

All applications sent by 12 September 2016 will receive full consideration. Later applications will be considered until the position is filled. Applicants are invited to contact Dr. Jahnke with any questions.

Scientific background of the project:'

Supermassive black holes (BHs) exist in most if not all (massive) galaxies. Since they grow from the same gas that also forms stars in the surrounding galaxy, the formation and evolution of black hole and stellar content of a galaxy are at least indirectly linked. In addition, the vast amounts of energy emitted when gas loses angular momentum and energy when falling towards the black hole, which then appears as an Active Galactic Nucleus (AGN), can potentially impact the gas in the galaxy. This "feedback" has been described theoretically in several different incarnations and is at least active by transport of energy through jets in galaxy clusters. Stronger impacts might be due, if highly accreting BHs were actually pushing gas out of the galaxy, potentially ending star formation.

Since the AGN-phases have such a potentially, though not finally established, impact on their galaxies and hence galaxy evolution in general, we set out to test in which instances these BHs actually start growing. The background is a paradigm from 1988 by Sanders et al. that optically luminous QSOs are a mere phase in the merger of gas-rich galaxies, which first produce an obscured AGN which then blows out gas. If this were true, then the AGN phases would be directly coupled to galaxy merging, which would then also be the instance in which star formation might be truncated.

We have already tested this "merger-AGN" paradigm in three studies, working our way through the parameter space: In Cisternas et al. (2011) we studied whether the AGN population dominating BH growth since z=1 actually shows a significantly higher prevalence of merger signatures compared to inactive galaxies. The resulting merger fractions were consistent, even though possibly mildly enhanced for AGN. We added to this by repeating this test for the highest mass BHs at z=2 (Mechtley et al. 2015) and z=0.2 (in prep.), both with similar results.

The final untested and yet centrally important part of parameter space are the BHs with the highest accretion rates. It is very plausible that for these some specifically large amount of gas has to be delivered or transported into the central region of the galaxy, and potentially the best or maybe only mechanism might be a major gas rich galaxy merger. This we want to test in this advertised PhD project.

We have obtained 21 orbits with the HST, imaging 21 QSOs at z=2 accrete at more than 30% of their Eddington accretion rate. These QSO images are to be analysed and compared to images of inactive galaxies from the CANDELS legacy fields, w.r.t. signs of recent gravitational disturbances. This will be done in cooperation with Dr. Matt Mechtley (Arizona State University), who will prepare this dataset for scientific exploitation.

The second dataset complements the first, with the same question asked for z=0.2, i.e. current times, as a difference to z=2 when BH growth peaked. For this, we have been granted 39h of imaging with VLT/FORS to observe a well selected sample of QSOs and matched inactive galaxies. This will be completed with a subset of QSOs observed with Subaru.

The candidate is expected to do hands on work with these data, to reduce and analyse the images, have them classified by other colleagues in a blind test, and to compile this into a comprehensive set of papers. As a result we will finally know whether galaxy mergers play a significant role at least for triggering the highest accretion rate black holes.

Skills:

The skillset we are looking for is quite diverse but there is time to learn a substantial fraction of these skills during the project. Overall the project will mainly require data analysis (preferably with Python) and statistics, and knowledge on galaxies and AGN. The first steps will require less data treatment but some working knowledge on statistical data analyis. Later, data reduction and analysis will become more important. In depth knowledge on galaxy evolution and AGN can be built up over time. Candidates should describe whether they have already some experience in these areas.

If you have further questions, please contact Knud Jahnke directly.