Dissipationless collapse and the dynamical mass-ellipticity relation of elliptical galaxies in Newtonian gravity and MOND
arXiv (Cornell University)(2023)
摘要
Context. Deur (2014) and Winters et al. (2023) proposed an empirical relation
between the dark to total mass ratio and ellipticity in elliptical galaxies
from their observed total dynamical mass-to-light ratio data M/L = (14.1 +/-
5.4)ϵ. In other words, the larger is the content of dark matter in the
galaxy, the more the stellar component would be flattened. Such observational
claim, if true, appears to be in stark contrast with the common intuition of
the formation of galaxies inside dark halos with reasonably spherical symmetry.
Aims. Comparing the processes of dissipationless galaxy formation in different
theories of gravity, and emergence of the galaxy scaling relations therein is
an important frame where, in principle one could discriminate them. Methods. By
means of collisionless N-body simulations in modified Newtonian dynamics (MOND)
and Newtonian gravity with and without active dark matter halos, with both
spherical and clumpy initial structure, I study the trends of intrinsic and
projected ellipticities, Sérsic index and anisotropy with the total dynamical
to stellar mass ratio. Results. It is shown that, the end products of both cold
spherical collapses and mergers of smaller clumps depart more and more from the
spherical symmetry for increasing values of the total dynamical mass to stellar
mass, at least in a range of halo masses. The equivalent Newtonian systems of
the end products of MOND collapses show a similar behaviour. The M/L relation
obtained from the numerical experiments in both gravities is however rather
different from that reported by Deur and coauthors.
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关键词
elliptical galaxies,newtonian gravity,mond,mass-ellipticity
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