Fornax 3D project: a two-dimensional view of the stellar initial mass function in the massive lenticular galaxy FCC 167

¹ University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA
e-mail: imartinn@ucsc.edu
² Max-Planck Institut für Astronomie, Konigstuhl 17, 69117 Heidelberg, Germany
³ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching b. München, Germany
⁴ University of Vienna, Department of Astrophysics, Türkenschanzstrasse 17, 1180 Vienna, Austria
⁵ Instituto de Astrofísica de Canarias, c/ Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
⁶ Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
⁷ Dipartimento di Fisica e Astronomia “G. Galilei”, Università di Padova, vicolo dell’Osservatorio 3, 35122 Padova, Italy
⁸ INAF–Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁹ INAF–Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Napoli, Italy
¹⁰ Department of Physics and Astronomy, Macquarie University, Sydney NSW 2109, Australia
¹¹ Australian Astronomical Observatory, PO Box 915, Sydney NSW 1670, Australia
¹² Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, UK
¹³ Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
¹⁴ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281, 9000 Gent, Belgium
¹⁵ Sterrewacht Leiden, Leiden University, Postbus 9513, 2300 RA Leiden, The Netherlands
¹⁶ Max-Planck-Institut fuer extraterrestrische Physik, Giessenbachstrasse, 85741 Garching bei München, Germany

Received: 25 February 2019
Accepted: 22 March 2019

Abstract

The stellar initial mass function (IMF) regulates the baryonic cycle within galaxies, and is a key ingredient for translating observations into physical quantities. Although it was assumed to be universal for decades, there is now growing observational evidence showing that the center of massive early-type galaxies hosts a larger population of low-mass stars than is expected based on observations from the Milky Way. Moreover, these variations in the IMF have been found to be related to radial metallicity variations in massive galaxies. We present here a two-dimensional stellar population analysis of the massive lenticular galaxy FCC 167 (NGC 1380) as part of the Fornax3D project. Using a newly developed stellar population fitting scheme, we derive a full two-dimensional IMF map of an early-type galaxy. This two-dimensional analysis allows us go further than a radial analysis, showing how the metallicity changes along a disk-like structure while the IMF follows a distinct, less disky distribution. Thus, our findings indicate that metallicity cannot be the sole driver of the observed radial IMF variations. In addition, a comparison with the orbital decomposition shows suggestive evidence of a coupling between stellar population properties and the internal dynamical structure of FCC 167, where metallicity and IMF maps seem to track the distribution of cold and warm orbits, respectively.