Radial variation of the stellar mass functions in the globular clusters M15 and M30: clues of a non-standard IMF?
We exploit a combination of high-resolution Hubble Space Telescope and wide-field ESO-VLT observations to study the slope of the global mass function (αG) and its radial variation (α(r)) in the two dense, massive and post core-collapse globular clusters M15 and M30. The available data set samples the clusters' main sequence down to ∼0.2 M⊙ and the photometric completeness allows the study of the mass function between 0.40 M⊙ and 0.75 M⊙ from the central regions out to their tidal radii. We find that both clusters show a very similar variation in α(r) as a function of clustercentric distance. They both exhibit a very steep variation in α(r) in the central regions, which then attains almost constant values in the outskirts. Such a behaviour can be interpreted as the result of long-term dynamical evolution of the systems driven by mass-segregation and mass-loss processes. We compare these results with a set of direct N-body simulations and find that they are only able to reproduce the observed values of α(r) and αG at dynamical ages (t/trh) significantly larger than those derived from the observed properties of both clusters. We investigate possible physical mechanisms responsible for such a discrepancy and argue that both clusters might be born with a non-standard (flatter/bottom-lighter) initial mass function.
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- December 2020
- stars: mass function;
- globular clusters: individual;
- Galaxy: kinematics and dynamics;
- galaxies: star clusters: general;
- Astrophysics - Astrophysics of Galaxies
- Accepted for publication by MNRAS