An international team of astronomers that includes University of Malta astronomer Joseph Caruana (Department of Physics, Institute for Space Sciences and Astronomy) has discovered glowing gas clouds surrounding distant quasars. Quasars are the cores of distant active galaxies, thought to be powered by material accreting onto a supermassive black hole at their centre, in the process emitting a great amount of radiation across the electromagnetic spectrum. The properties of the halos surrounding these quasars disagree with currently accepted theories of galaxy formation in the early universe.
The team used an instrument called MUSE on the European Southern Observatory’s Very Large Telescope in Chile to carry out their observations. Their work suggests that halos surrounding quasars are much more common than expected. Whereas in previous studies only 10% of quasars were found to have such halos, in this new study with MUSE, all 19 quasars observed (which were chosen from among the brightest that MUSE can observe) exhibited halos. This is thought to be due the massive increase in MUSE's observing power over similar instruments, but more observations are required to confirm this. “It is still too early to say if this is due to our new observational technique or if there is something peculiar about the quasars in our sample. So there is still a lot to learn; we are just at the beginning of a new era of discoveries”, says lead author Elena Borisova, from the ETH Zurich.
The set of discovered halos also had another surprise in store: their temperature is around 10 000 degrees Celsius. This is in strong disagreement with currently accepted models of the structure and formation of galaxies, which suggest that gas so close to the galaxies should have temperatures higher than a million degrees.
Co-author Sebastiano Cantalupo remarked: “We have exploited the unique capabilities of MUSE in this study, which will pave the way for future surveys. Combined with a new generation of theoretical and numerical models, this approach will continue to provide a new window on cosmic structure formation and galaxy evolution.”
Joseph Caruana commented on the fantastic capabilities of MUSE: "This instrument allows one to obtain images and spectra simultaneously; essentially, you have a spectrum for every single pixel. So for every pixel, you can look at how the light's intensity varies across a range of wavelengths. MUSE offers a wide field of view while boasting high spatial resolution and a fairly large spectral range."
The team is composed of Elena Borisova, Sebastiano Cantalupo, Simon J. Lilly, Raffaella A. Marino and Sofia G. Gallego (Institute for Astronomy, ETH Zurich, Switzerland), Roland Bacon and Jeremy Blaizot (University of Lyon, Centre de Recherche Astrophysique de Lyon, Saint-Genis-Laval, France), Nicolas Bouché (Institut de Recherche en Astrophysique et Planétologie, Toulouse, France), Jarle Brinchmann (Leiden Observatory, Leiden, The Netherlands; Instituto de Astrofísica e Ciências do Espaço, Porto, Portugal), C Marcella Carollo (Institute for Astronomy, ETH Zurich, Switzerland), Joseph Caruana (Department of Physics, University of Malta, Msida, Malta; Institute of Space Sciences & Astronomy, University of Malta, Malta), Hayley Finley (Institut de Recherche en Astrophysique et Planétologie, Toulouse, France), Edmund C. Herenz (Leibniz-Institut für Astrophysik Potsdam, Potsdam, Germany), Johan Richard (Univ Lyon, Centre de Recherche Astrophysique de Lyon, Saint-Genis-Laval, France), Joop Schaye and Lorrie A. Straka (Leiden Observatory, Leiden, The Netherlands), Monica L. Turner (MIT-Kavli Center for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA), Tanya Urrutia (Leibniz-Institut für Astrophysik Potsdam, Potsdam, Germany), Anne Verhamme (University of Lyon, Centre de Recherche Astrophysique de Lyon, Saint-Genis-Laval, France), Lutz Wisotzki (Leibniz-Institut für Astrophysik Potsdam, Potsdam, Germany).