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The quantity of dark matter in early-type galaxies and its relation to the environment

A. Nigoche-Netro, G. Ramos-Larios, P. Lagos, E. de la Fuente, A. Ruelas-Mayorga, J. Méndez-Abreu, S. N. Kemp, R. J. Diaz

Abstract
We study the behaviour of the dynamical and stellar mass inside the effective radius of early-type galaxies (ETGs) as a function of environment considering Newtonian dynamics, different surface-brightness profiles, different initial mass functions (IMF), and different redshift ranges. We use several samples of ETGs – ranging from 19 000 to 98 000 objects – from the ninth data release of the Sloan Digital Sky Survey. We assume that any difference between the dynamical and stellar mass is due to dark matter and/or a non-universal IMF. The main results, considering samples in the redshift range 0.0024 ≤ z ≤ 0.35, are as follows: (i) the amount of dark matter inside ETGs depends on the environment; (ii) ETGs in low-density environments span a wider dark matter range than ETGs in dense environments; (iii) the amount of dark matter inside ETGs in the most dense environments will be less than approximately 55–75 per cent of the dynamical mass; (iv) the accurate value of this upper limit depends on the impact of the IMF on the stellar mass estimation; (v) in the case of an ETG sample which is approximately complete for log(MVirial/MSun) > 10.5 and in the redshift range 0.04 ≤ z ≤ 0.08, we find that the amount of dark matter in the most dense environments will be less than approximately 60–65 per cent of the dynamical mass.

Keywords
galaxies: distances and redshifts, galaxies: fundamental parameters, galaxies: photometry, dark matter

Monthly Notices of the Royal Astronomical Society
Volume 488, Issue 1, Page 1320
2019 September

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia