Imprint of the galactic acceleration scale on globular cluster systems

M Bílek,S Samurović,F Renaud

doi:10.1051/0004-6361/201936158

Abstract

We report that the density profiles of globular cluster (GC) systems in a sample of 17 early-type galaxies (ETGs) show breaks at the radii where the gravitational acceleration exerted by the stars equals the galactic acceleration scale a0 known from the radial acceleration relation or the modified Newtonian dynamics (MOND). The match with the other characteristic radii in the galaxy is not that close. We propose possible explanations in the frameworks of the Lambda cold dark matter (ΛCDM) model and MOND. We find tentative evidence that in the ΛCDM context, GCs reveal not only the masses of the dark halos through the richness of the GC systems but also the concentrations through the break radii of the GC systems.

Highlights

Radial surface density profiles of globular cluster (GC) systems have traditionally been described either by a power law or by a Sérsic profile
We report that the density profiles of globular cluster (GC) systems in a sample of 17 early-type galaxies (ETGs) show breaks at the radii where the gravitational acceleration exerted by the stars equals the galactic acceleration scale a0 known from the radial acceleration relation or the modified Newtonian dynamics (MOND)
Assuming the standard ΛCDM framework, Navarro et al (2017) proposed that the MOND-like behavior in spiral galaxies stems from the following factors: 1) the galaxies are embedded in dark halos with Navarro-Frenk-White (NFW) profiles (Navarro et al 1996), 2) the mass of the halo correlates with the baryonic mass of the galaxy, 3) the baryonic mass of a disk galaxy correlates with the scale length of its exponential profile, and 4) the rotation curves can only be observed to about five scale lengths

Summary

Introduction

Radial surface density profiles of GC systems have traditionally been described either by a power law or by a Sérsic profile (see, e.g., the review Brodie & Strader 2006). We report that the break radii rbr are very close to the radii where the gravitational accelerations generated by the stars of the galaxies equal the much discussed galactic acceleration scale a0 and suggest possible explanations in the frameworks of the Lambda cold dark matter (ΛCDM) model and modified Newtonian dynamics (MOND). In the present work we report that the galactic acceleration scale is imprinted even in the number density profiles of GC systems of ETGs since they show abrupt breaks near the radii where the gravitational accelerations caused by stars equal a0. If larger galaxy samples confirm our observation, the breaks in the density profiles of GC systems can be used to estimate the dark halo concentration when working in the ΛCDM framework.

Break radii of GC systems

Discussion and conclusions