Variations in the Milky Way's Stellar Mass Function at [Fe/H] < -1
Abstract
We present the first determination of the Galactic stellar mass function (MF) for low-mass stars (0.2-0.5 M_sun) at metallicities [Fe/H] < -1. A sample of ~53,000 stars was selected as metal-poor on the basis of both their halo-like orbits and their spectroscopic [Fe/H] from Gaia DR3 BP/RP (XP) spectra. These metallicity estimates for low-mass stars were enabled by calibrating Gaia XP spectra with stellar parameters from SDSS-V. For -1.5 < [Fe/H] < -1, we find that the MF below 0.5 M_sun exhibits a "bottom-heavy" power-law slope of alpha ~ -1.6. We tentatively find that at even lower metallicities, the MF becomes very bottom-light, with a near-flat power-law slope of alpha ~ 0 that implies a severe deficit of low-mass stars. This metallicity-dependent variation is insensitive to the adopted stellar evolution model. These results show that the Galactic low-mass MF is not universal, with variations in the metal-poor regime. A further calibration of XP metallicities in the regime of M < 0.5 M_sun and [Fe/H] < -1.5 will be essential to verify these tentative low-metallicity trends.
Cite
@article{arxiv.2601.19522,
title = {Variations in the Milky Way's Stellar Mass Function at [Fe/H] < -1},
author = {Jiadong Li and Hans-Walter Rix and Yuan-Sen Ting and Yu-Ting Wang and Szabolcs Mészáros and Ilija Medan and Chao Liu and Zhiqiang Yan and Peter J. Smith and Dan Qiu and Alexandre Roman-Lopes and Gregory M. Green and Danny Horta and Zachary Way and Tadafumi Matsuno and Stefano Souza and José G. Fernández-Trincado},
journal= {arXiv preprint arXiv:2601.19522},
year = {2026}
}
Comments
15 pages, 9 figures, 5 tables, Accepted for publication in ApJL