The integrated galaxy-wide stellar initial mass function over the radial acceleration range of early-type galaxies

Abstract

The observed radial accelerations of 462 Early-type galaxies (ETGs) at their half-mass radii are discussed. They are compared to the baryonic masses of the same galaxies, which are derived from theoretical expectations for their stellar populations and cover a range from ≈104 M⊙ to ≈1011 M⊙. Both quantities are plotted against each other, and it is tested whether they lie (within errors) along theoretical radial acceleration relations (RARs). We choose the Newtonian RAR and two Milgromian, or MONDian RARs. At low radial accelerations (corresponding to low masses), the Newtonian RAR fails without non-baryonic dark matter, but the two MONDian ones may work, provided moderate out-of-equilibrium dynamics in some of the low-mass ETGs. However all three RARs fail at high accelerations (corresponding to high masses) if all ETGs have formed their stellar populations with the canonical stellar initial mass function (IMF). A much better agreement with the observations can however be accomplished, if the theory of the integrated galaxy-wide stellar initial mass functions (IGIMFs) is used instead. This is because the IGIMF-theory predicts the formation of an overabundance of stellar remnants during the lifetime of the massive ETGs. Thus their baryonic masses today are higher than they would be if the ETGs had formed with a canonical IMF. Also the masses of the stellar-mass black holes should be rather high, which would mean that most of them probably formed when the massive ETGs were not as metal-enriched as they are today. The IGIMF-approach confirms downsizing.

The Variation in the Galaxy-wide Initial Mass Function for Low-mass Stars: Modeling and Observational Insights

“…Unfortunately, these studies have primarily presented IMF results in terms of the IMF mismatch parameter, a ratio of the expected and observed mass-to-light ratio. This parameter is contingent on stellar remnant mass and, consequently, the IMF slope of massive stars and the poorly constrained SFH of a galaxy (Yan et al 2017(Yan et al , 2019bDabringhausen & Kroupa 2023).…”

“…The variation in the massive end of the IMF alters the stellar-to-remnant mass ratio across different galaxies and even at various radii for the same galaxy. Consequently, constraints derived from the dynamical mass-tolight ratio, coupled with chemical enrichment, play an inseparable role in shaping our understanding of the galaxy-wide IMF of ETGs (Yan et al 2021;Dabringhausen & Kroupa 2023).…”

A Strong Falsification of the Universal Radial Acceleration Relation in Galaxies

“…For example, the RAR shown in galaxies is not consistent with the data of galaxy clusters (Chan & Del Popolo 2020;Chan & Law 2022). Also, whether the RAR can be applied in elliptical galaxies is controversial (Chae et al 2020;Dabringhausen & Kroupa 2023). Generally speaking, verifying or falsifying the RAR requires very high-quality measurements of rotation velocity in galaxies.…”