Scientific research

Without going into painful amounts of detail, my interests lie in the formation and evolution of galaxies. My work is mostly observational in method, and derives from data obtained mostly from the Hubble Space Telescope (HST) (in low earth orbit), the ESO Very Large Telescope (VLT) (in the Atacama desert, Chile), and the Canada France Hawaii Telescope (CFHT) (on Mauna Kea, Hawaii). Smaller contributions come from the Spitzer Space Telescope, Chandra X-ray Observatory, Gran Telescopio Canarias, ESO New Technology Telescope, Nordic Optical Telescope, Green Bank Radio Telescope, and probably more. Sometimes, however, I have to rely upon simulation data, for which we use large supercomputers.

Central in the field of galaxy evolution are questions such as when did the universe form its stars and how has this process proceeded over cosmic history. I.e. how do the properties of galaxy populations evolve over cosmic time in quantities such as stellar mass, stellar age, etc.)? Since stars are factories for dust and metals, how have the dust and metal contents of galaxies evolved with cosmic epoch? Star-formation and the associated supernova explosions also generate winds, which will expel these metals into the intergalactic medium, so understanding this feedback is vital in almost all studies. However if winds are flowing out, how do galaxies acquire the gas they need to fuel the formation of stars? Can gas flow in and out of galaxies at the same time? How are all these processes related to environment? How has the large-scale structure of the universe - its dark matter haloes - evolved and how does this affect the star formation process? How are these processes - i.e. those related to star formation - all tied up with the formation of active galactic nuclei and super-massive black holes? Do they trigger or quench star formation and how did stars and black holes co-evolve? Which objects re-ionized the intergalactic medium and how did the process proceed? That's quite a lot of questions... Furthermore, of particular importance when observationally addressing any astrophysical phenomenon: how does an observable quantity relate to the underlying physical conditions?

We investigate some of the above questions in a number of ways.

  • We perform our own surveys for galaxies in the distant universe. Here we search for some of the most distant galaxies in the universe by using the Lyman-break/'dropout' technique using optical and near infrared broadband imaging data. These data have been obtained from CFHT (WUDS; the WIRCam Ultra-Deep Survey) and VLT/HAWI-I, targeting blank fields and lensing clusters, respectively. We then follow them up with ground-based spectrographs on big telescopes such as VLT/X-Shooter, and will use GTC/EMIR and VLT/KMOS when they come online. The best source of information on these projects would be the REGALDIS page.
  • As well as finding galaxies by virtue of their stellar continuum we also select high-z galaxies by virtue of their nebular emission lines, particularly the Lyman-alpha (Lyα) and H-alpha (Hα) lines. Particularly with respect to Lyα emitters, this has the big virtue of being sensitive to the least massive detectable galaxies, which also happen to be the most abundant. The disadvantage is that Lyα data are notoriously difficult to interpret. That, however, is the bulk of the fun. For this we also use VLT and CFHT, with other components of the full data sets coming from the Nordic Optical Telescope, and exploiting large Hubble Space Telescope surveys. The best place to read about these programmes is on my high-z Lyα page.
  • Above, we alluded to the importance of Lyα studies at cosmological distances, but also pointed out that the line is difficult to interpret. It therefore needs detailed empirical study, which due to the enormous distances involved, cannot be performed on distant galaxies. We therefore turn to actively star-forming galaxies in the local universe that can be studied in exquisite detail with Hubble observations, together with a huge array of ancillary data at various wavelengths from many other telescopes. The best place to read about this is on the LARS page (which is incomplete), or on the data distribution page for the pilot studies.
  • As well as observations in the Lyα line, it is also the subject of an impressive body of theoretical investigations. The origin of the interpretation difficulties of Lyα stem from the fact it is a resonance line: it scatters off neutral hydrogen atoms in the interstellar medium, and its path through a galaxy is unpredictable in any realistic case. The situation is so complicated that no analytical formalisms can really do justice to the problem, and so we fall into the less elegant, but infinitely flexible, world of computer simulations. Read more about this on my radiation transport page or in look up any paper on which Anne Verhamme is an author.
  • The Spitzer IRAC-MIPS Extragalactic Survey (SIMES) is beginning...
  • I collaborate on various other projects relating to cosmology and starburst astrophysics. Specifically the Stockholm VIMOS Supernova Survey (SVISS), which searches for core-collapse supernova (as well as thermonuclear ones) out to a redshift of around 1, and detailed studies of young star clusters in blue compact galaxies in the nearby universe. For these you should see a series of articles by Jens Melinder (and also his PhD thesis), and the webpage of Angela Adamo (and also her PhD Thesis).