The stellar Initial Mass Function of the solar neighbourhood revealed by Gaia

A. Sollima

Published 2019-04-11Version 1

I use a sample of more than 130,000 stars in the solar neighbourhood with parallaxes, magnitudes and colours estimated with unprecedented accuracy by the second data release of the Gaia mission to derive the initial mass function of the Galactic disc. A full-forward technique is employed to take into account for the population of unresolved binaries, the metallicity distribution, the star formation history and their variation across the Galactic disk as well as all the observational effects. The shape of the initial mass function is well represented by a segmented power-law with two characteristic break masses. It has a peak at M~0.15 Ms with a significant depletion of lower mass stars and a slope of alpha=-1.42 +/- 0.08 in the range 0.15 < M/Ms < 1. Above 1 Ms the IMF shows an abrupt decline with a slope alpha=-2.69 +/- 0.16, steeper than a Salpeter (1955) law. The comparison with the mass functions estimated in unevolved stellar systems suggests a variation incompatible with the quoted uncertainties which might be interpreted as a genuine primordial variation or as due to a significant intrinsic variance.