A possible solution to the Milky Way's binary-deficient retrograde stellar population Evidence that omega Centauri has formed in an extreme starburst
Abstract
Context. The fraction of field binaries on retrograde orbits about the Milky Way is significantly lower compared to its prograde counterpart.
Chemical and dynamical evidence suggests that the retrograde stellar population originates from omega Centauri, which is either the most massive globular cluster (GC) of the Milky Way or the putative core of a former dwarf galaxy. Aims.
Star formation conditions required to produce the retrograde binary population are constrained assuming that the retrograde stellar population originates from omega Centauri's progenitor. Methods.
We match the observed low binary fraction with dynamical population synthesis models, including a universal initial binary population and dynamical processing in star clusters, making use of the publicly available binary population synthesis tool BIPOS1. Results.
It is found that either the GC progenitor of omega Cen must have formed with a stellar density of approximate to 10(8) M-circle dot pc(-3) or the omega Centauri dwarf galaxy's progenitor star cluster population must have formed in an extreme starburst with a star formation rate exceeding 1000 M-circle dot yr(-1) and probably a top-heavy embedded-cluster mass function with suppressed low-mass cluster formation. The separation and mass-ratio distribution for retrograde field binaries are predicted for comparison with future observations.
Conclusions. A viable solution for the deficiency of binaries on retrograde orbits is presented, and star formation conditions for omega Centauri as well as orbital parameter distributions for the Milky Way's retrograde binary population are predicted.
The dwarf galaxy origin for omega Centauri is tentatively preferred within the present context.