Leader: Diego Ignacio Salvador Campe

Email: diego.salvador@hdr.mq.edu.au

Collaborators:

– Matt Owers (Macquarie University)
– Andrew Hopkins (Macquarie University)

We welcome any additional collaborators who are interested in contributing to this project.

Topic: The unexpected dynamics of low-mass dwarf galaxies

Status: under review by Science Committee

Abstract:

The initial mass function (IMF) describes the distribution of stellar masses in newly formed stellar populations and plays a critical role in understanding star formation and galaxy evolution. Despite over 60 years of study, two fundamental questions about the IMF remain unresolved: (i) its variability—whether the IMF remains invariant in different environments, as suggested by studies in nearby resolved systems; and (ii) its scale dependence—at what spatial scale the IMF is fully sampled, and how measurements of the IMF at local (spaxel) and global (galaxy-integrated) scales relate to each other. While prior studies have explored the IMF’s high- and low-mass ends independently, a comprehensive analysis covering both ends at multiple spatial scales is still lacking.

This project builds on our previous work with 1,344 star-forming galaxies from the SAMI survey, where we analysed the high-mass IMF slope at both spaxel and integrated scales. We now seek to extend this analysis to the low-mass end using Hector data. Hector’s full wavelength coverage and spectral resolution are essential for this study, enabling the detailed characterisation of key spectral features sensitive to IMF variations. Specifically, we will use Hector spectra alongside the MILES stellar population synthesis models, applying a Bayesian fitting algorithm based on the approach developed by Navarro et al. (2019, 2024). This method identifies the optimal combination of stellar parameters ([M/H], [Mg/Fe], [Na/Fe], [Ti/Fe], and the IMF slope) by fitting absorption features known to be sensitive to IMF variations—Mgb, Fe5270, Fe5335, NaD, TiO1, and TiO2.

Our goal is to measure the low- and high-mass IMF slopes simultaneously across Hector’s sample of star-forming galaxies, providing new insights into how the IMF varies across mass regimes. This dual-scale analysis will also explore how local IMF variations (spaxel-scale) contribute to the globally measured IMF, offering a deeper understanding of the interplay between resolved and integrated stellar populations. By leveraging Hector’s capabilities, this study will advance our knowledge of IMF behaviour across spatial scales and help address long-standing questions about the IMF’s universality and scaling properties.

*NOTE: “Topic” ticked box does not apply.

Needed data products:

Emission line fits.
Aperture spectra (1Re or other apertures).
Galaxy spectral classification.

Publication Date: 25/07/2025