Result: Systematic variation of the stellar initial mass function in early―type galaxies
Gemini Observatory, Northern Operations Centre, 670 North A'ohoku Place, Hilo, Hawaii 96720, United States
European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
Sterrewacht Leiden, Leiden University, Postbus 9513, 2300 RA Leiden, Netherlands
Laboratoire AIM Paris-Saclay, CEA/IRFU/SAp CNRS Unlversité Paris Diderot, 91191 Gif-sur-Yvette, France
Université Lyon 1, Observatoire de Lyon, Centre de Recherche Astrophysique de Lyon and Ecole Normale Supérieure de Lyon, 9 avenue Charles André, 69230 Saint-Genis Laval, France
Max-Planck Institut für extraterrestrische Physik, PO Box 1312, 85478 Garching, Germany
Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, Netherlands
Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, Netherlands
Max-Planck Institut für Astrophysik, KarlSchwarzschild-Strasse 1, 85741 Garching, Germany
Department of Astronomy, Campbell Hall, University of California, Berkeley, California 94720, United States
Centre for Astrophysics Research, University of Hertfordshire, Hatfield AL1 9AB, United Kingdom
Centre for Astrophysics & Supercomputing, Swinburne University of Technology, PO Box 218, Hawthorn, Victoria 3122, Australia
Dunlap Institute for Astronomy & Astrophysics, University of Toronto, 50 St George Street, Toronto, Ontario M5S 3H4, Canada
Physics Department, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801, United States
Observatoire de Paris, LERMA and CNRS, 61 Avenue de l'Observatoire, 75014 Paris, France
Department of Astrophysics, University of Massachusetts, 710 North Pleasant Street, Amherst, Massachusetts 01003, United States
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Further Information
Much of our knowledge of galaxies comes from analysing the radiation emitted by their stars, which depends on the present number of each type of star in the galaxy. The present number depends on the stellar initial mass function (IMF), which describes the distribution of stellar masses when the population formed, and knowledge of it is critical to almost every aspect of galaxy evolution. More than 50 years after the first IMF determination1, no consensus has emerged on whether it is universal among different types of galaxies2. Previous studies indicated that the IMF and the dark matter fraction in galaxy centres cannot both be universal3―7, but they could not convincingly discriminate between the two possibilities. Only recently were indications found that massive elliptical galaxies may not have the same IMF as the Milky Way8. Here we report a study of the two-dimensional stellar kinematics for the large representative ATLAS3D sample9 of nearby early-type galaxies spanning two orders of magnitude in stellar mass, using detailed dynamical models. We find a strong systematic variation in IMF in early-type galaxies as a function of their stellar mass-to-light ratios, producing differences of a factor of up to three in galactic stellar mass. This implies that a galaxy's IMF depends intimately on the galaxy's formation history.