Survey of gravitationally-lensed objects in HSC imaging (SuGOHI)

III. Statistical strong lensing constraints on the stellar IMF of CMASS galaxies^⋆

¹ Leiden Observatory, Leiden University, Niels Bohrweg 2, 2333 Leiden, The Netherlands
e-mail: sonnenfeld@strw.leidenuniv.nl
² Kavli IPMU (WPI), UTIAS, The University of Tokyo, Kashiwa, Chiba 277-8583, Japan
³ Faculty of Science and Engineering, Kindai University, Higashi-Osaka 577-8502, Japan
⁴ Astronomical Institute, Tohoku University, Aramaki, Aoba, Sendai 980-8578, Japan
⁵ Institute of Physics, Laboratory of Astrophysics, École Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, 1290 Versoix, Switzerland
⁶ The Inter-University Center for Astronomy and Astrophysics, Post bag 4, Ganeshkhind, Pune 411007, India
⁷ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild Str. 1, 85741 Garching, Germany
⁸ Physik-Department, Technische Universität München, James-Franck-Straße 1, 85748 Garching, Germany
⁹ Institute of Astronomy and Astrophysics, Academia Sinica, 11F of ASMAB, No.1, Section 4, Roosevelt Road, Taipei 10617, Taiwan
¹⁰ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹¹ Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
¹² Research Center for the Early Universe, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
¹³ National Optical Astronomy Observatory, 950 N Cherry Ave, Tucson, AZ 85719, USA

Received: 21 April 2019
Accepted: 11 July 2019

Abstract

Context. The determination of the stellar initial mass function (IMF) of massive galaxies is one of the open problems in cosmology. Strong gravitational lensing is one of the few methods that allow us to constrain the IMF outside of the Local Group.

Aims. The goal of this study is to statistically constrain the distribution in the IMF mismatch parameter, defined as the ratio between the true stellar mass of a galaxy and that inferred assuming a reference IMF, of massive galaxies from the Baryon Oscillation Spectroscopic Survey (BOSS) constant mass (CMASS) sample.

Methods. We took 23 strong lenses drawn from the CMASS sample, measured their Einstein radii and stellar masses using multi-band photometry from the Hyper Suprime-Cam survey, then fitted a model distribution for the IMF mismatch parameter and dark matter halo mass to the whole sample. We used a prior on halo mass from weak lensing measurements and accounted for strong lensing selection effects in our model.

Results. Assuming a Navarro Frenk and White density profile for the dark matter distribution, we infer a value μ_IMF = −0.04 ± 0.11 for the average base-10 logarithm of the IMF mismatch parameter, defined with respect to a Chabrier IMF. A Salpeter IMF is in tension with our measurements.

Conclusions. Our results are consistent with a scenario in which the region of massive galaxies where the IMF normalisation is significantly heavier than that of the Milky Way is much smaller than the scales 5 − 10 kpc probed by the Einstein radius of the lenses in our sample, as recent spatially-resolved studies of the IMF in massive galaxies suggest.