The Initial Mass Function of Lens Galaxies from Quasar Microlensing

TL;DR

This paper introduces a novel method using quasar microlensing to estimate the stellar initial mass function parameters in lens galaxies, providing new constraints on the low-mass slope and cutoff.

Contribution

It presents a new approach to determine the IMF in external galaxies through microlensing measurements without assuming a specific IMF shape.

Findings

Estimated mean stellar mass: 0.16 solar masses

IMF low-mass slope: -2.6 ± 0.9

Low-mass cutoff: 0.13 ± 0.07 solar masses

Abstract

We present a new approach in the study of the Initial Mass function (IMF) in external galaxies based on quasar microlensing observations. We use measurements of quasar microlensing magnifications in 24 lensed quasars to estimate the average mass of the stellar population in the lens galaxies without any a priori assumption on the shape of the IMF. The estimated mean mass of the stars is $\langle M \rangle =0.16^{+0.05}_{-0.08} M_\odot$ (at 68\% confidence level). We use this average mass to put constraints into two important parameters characterizing the IMF of lens galaxies: the low-mass slope, $\alpha_2$, and the low-mass cutoff, $M_{low}$. Combining these constraints with prior information based on lensing, stellar dynamics, and absorption spectral feature analysis, we calculate the posterior probability distribution for the parameters $M_{low}$ and $\alpha_2$. We estimate values for the low-mass end slope of the IMF $\langle \alpha_2\rangle=-2.6\pm 0.9$ (heavier than that of the Milky Way) and for the low-mass cutoff $\langle M_{low}\rangle=0.13\pm0.07$. These results are in good agreement with previous studies on these parameters and remain stable against the choice of different suitable priors.