Upcoming Physics & Astronomy Climate, Earth & Environment

Cosmological hydrodynamical simulations with calibrated non-universal initial mass functions

Funder STFC (part of UKRI)
Recipient organisation Liverpool John Moores University
Funding Not disclosed
Period Oct 2027 — Oct 2027

In plain English

AI plain-English summary

Galaxies like our own may be hiding a secret population of dwarf stars that changes how we understand their evolution. This project will test whether the mix of stars in a galaxy—the "initial mass function" (IMF)—varies depending on where and when stars form, rather than being fixed as most models currently assume. Recent observations of massive elliptical galaxies show they contain more mass than their starlight suggests. The leading explanation is an overabundance of faint, low-mass dwarf stars that add weight without adding brightness. If true, this variable IMF would alter how galaxies recycle gas, form new stars, and explode as supernovae—processes that current simulations treat with a universal IMF. The researcher will calibrate a variable IMF using observed mass-to-light excesses, then embed it into a state-of-the-art hydrodynamical simulation of galaxy formation. Running the simulation self-consistently will reveal how a non-universal IMF changes predictions for galaxy growth, star formation rates, and feedback from dying stars. This is fundamental science with no immediate practical application. Understanding how galaxies assemble their stars, however, underpins everything from interpreting telescope surveys to modelling the chemical enrichment that seeded planets—and, eventually, life.

View original technical description
This project aims to analyse how implementing a calibrated variable stellar initial mass function (IMF) into a modern large-scale hydrodynamical simulation affects wider galactic properties. A universal IMF fixes the distribution of mass within a stellar population independent of the conditions under which the stars formed. This is a widely accepted approximation in galaxy formation models, but recent observations of high-mass early-type galaxies (ETGs) indicate excesses in their mass-to-light ratios in comparison to the Milky Way. The mass-to-light excess (MLE) can be corrected by adapting the IMF to allow an overabundance of low-mass dwarf stars (making the IMF bottom-heavy in mass) and/ or stellar remnants (making the IMF top-heavy) such that the mass in stars in ETGs is increased without altering the luminosity of the stars. Implementing a variable IMF that explains the observed MLE into a galaxy formation model will subsequently affect stellar feedback and stellar formation rates among other galactic processes, meaning that simulations must be altered and run self-consistently in order to accurately analyse how a variable IMF may affect the evolution of galaxies. To this end, this project will calibrate a variable IMF based on observed MLE relations and analyse how incorporating this IMF into a state-of-the-art hydrodynamical simulation affects galaxy properties.

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Researchers

Anna Durrant (Student)

Related Research

Grants with similar aims, by meaning.

The Radial Dependence of the Stellar Initial Mass Function in Massive Galaxies
Variations in the initial mass function across the galaxy population
Bringing together star formation and galaxy formation calculations to interpret the stellar populations of galaxies (Astronomy Theory)
Strong Lensing, Stellar Dynamics and the IMF in Elliptical Galaxies
Non-kinematical anisotropies in galaxy clustering and cosmological tests of gravity

Original classification

Studentship

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