The new technique for the determination of the stellar initial mass function of unresolved stellar populations

TL;DR

This paper introduces a new pixel-space spectral fitting technique to accurately determine the low-mass slope of the stellar initial mass function in unresolved stellar populations, especially for systems with long relaxation times.

Contribution

It extends the NBursts spectral fitting method to include IMF determination from integrated light spectra, validated through Monte-Carlo simulations.

Findings

High precision in age, metallicity, and IMF for high S/N data.

Adding M/L information improves IMF slope accuracy.

Systematic M/L errors affect IMF slope estimates.

Abstract

We present the new technique for the determination of the low-mass slope of the stellar mass function from the pixel-space fitting of integrated light spectra. This technique is the extension of the NBursts full spectral fitting technique. It can be used to constrain the stellar initial mass function (IMF) of compact stellar systems having high relaxation timescales (Hubble time or more). We used Monte-Carlo simulations with mock spectra to test the technique and conclude that: (1) age, metallicity, and IMF can be very precisely determined in the first "unrestricted" variant of the code for high signal-to-noise datasets (S/N=100, R=7000 give the uncertainty of alpha of about 0.1); (2) adding the M/L information significantly improves the precision and reduces the degeneracies, however systematic errors in M/L will translate into offsets in the IMF slope.