Research
My research is in general focussed on the nature of
galaxies
in the early
universe. During my graduate studies 1996-2000 I worked on this topic (under
the supervision of Palle Møller and Bjarne Thomsen) by studying
so called Damped Ly-α
Absorbers (DLAs). These objects are high
redshift galaxies found via the absorption they cause in the spectra of
yet more distant and bright QSOs. The advantage of DLAs for the study of
high redshift galaxies is that they are absorption selected from
the pool of galaxies present at these early epochs. The consequence of
this is that it allows an independent look at the high redshift galaxy
population with different selection effects than for high redshift galaxies
identified via their emission. Perhaps more
importantly a wealth of information about the chemical enrichment of the
galaxies can be derived from the study of absorption lines in the
spectrum of the QSO due to metals in the absorbers. My thesis can be
found here. In my thesis thre were two main results: 1) an exploration of the relation between DLAs and a new population of galaxies called "Lyman-break galaxies" (see below). I found in the thesis that DLAs must belong to a much more numerous population of fainter galaxies than the Lyman-break galaxies found at the time. 2) we found the first (or at least one of the first) example of what has later been known as "Lyman-alpha blobs".
After finishing my PhD I had the honour of work as a fellow at ESO. This allowed
my to continue my collaboration with Palle Møller and this collaboration has continued throughout my career. This has been and still is great.
My interest next turned towards studying the properties of high redshift galaxies selected also in other ways
than via absorption. In the period 2000-2010 I mainly focused on
Gamma Ray Bursts and
the galaxies hosting them, and on
Ly-α emission
selected galaxies. The work on Ly-α emission led to my involvement in
the Ultra-VISTA survey as one of four co-PIs.
Bo Milvang-Jensen has been absolutely instrumental for this work. The work on GRBs led to the very surprising discovery of GRBs without associated supernovae: No supernovae associated with two long-duration gamma-ray bursts. I also had the honour of leading a large international collaboration that worked on building complete samples of GRB follow-up observations. Two of the many papers from that effort can be seen here: Low-resolution Spectroscopy of Gamma-ray Burst Optical Afterglows: Biases in the Swift Sample and Characterization of the Absorbers, The X-shooter GRB afterglow legacy sample (XS-GRB).
As mentioned I was also interested in
Lyman Break selected,
and
ISO/SCUBA selected galaxies, and in general in understanding
how these different pieces to the `Galaxy Formation puzzle' can be fitted
together to a consistent picture. This line of work I have followed throughout my career and some of the results from our group are in these papers:
Reconciling the Metallicity Distributions of Gamma-Ray Burst, Damped Ly-alpha, and Lyman Break Galaxies at z = 3 and
High-redshift damped Ly-alpha absorbing galaxy model reproducing the N(HI) - Z distribution.
In 2004 I started as associate professor at the Niels Bohr Institute and in 2005 Jens Hjorth, Anja Andersen, Kristian Pedersen, Jesper Sollerman, Darach Watson and I started the Darck Cosmology centre. That DG center ran from 2005 to 2015, which was an exiting period with
lots of interesting research.
Starting around 2010 my interest turned towards dust both in DLAs and GRB host galaxies. In particular, I started an activity searching for dusty and metal rich
DLAs by searching for red quasars. This led to a lot of interesting work that is still ongoing. Instrumental for this work has been and still is Jens-Kristian Krogager, Kasper Heintz, Stefan Geier who I have all had the pleasure of supervising. An example of this work can be found in this paper led by Stefan Geier:
Gaia-assisted selection of a quasar reddened by dust in an extremely strong damped Lyman-α absorber at z = 2.226. Together with emeritus Erik Hoeg I started thinking about how the astrometric mission Gaia could be used to build an unbiased sample of quasars. This has so far led to three papers describing the technique and the result of a pilot study: A study of purely astrometric selection of extragalactic point sources with Gaia, Unidentified quasars among stationary objects from Gaia DR2, Spectroscopic classification of a complete sample of astrometrically-selected quasar candidates using Gaia DR2. This work is still ongoing and we hope to use the technique to build a sample large enough to draw groundbreaking conclusions on both quasar populations and dusty DLAs.
In these years I spend most of my research time working on a new spectrograph and imager for the Nordic Optical Telescope: NOT Transient Explorer. This is a very ambitious project that hopefully will be completed in 2022 (COVID doesn't help). The project is mainly funded by the Carlsberg Foundation, but also with contributions from a list of other very good partners.
I also spend a lot of time applying for money with very poor succees. If there was one thing I could change in the way we conduct research today it would be this in my view absurd funding situation. I have also written about that - see under Outreach and Public Debate (see what I wrote in Biozoom and Science Report).
You can find more information on all these topics
in the Level5 knowledgebase
and among my publications.
Last updated : Dec 29, 2020