Modeling the Ages and Metallicities of Early-Type Galaxies in Fundamental Plane Space

TL;DR

This paper uses a semi-analytic model based on cosmological simulations to predict the structural and stellar population properties of early-type galaxies, successfully reproducing observed correlations between age, metallicity, and velocity dispersion.

Contribution

It introduces a model that links galaxy assembly history to observable properties, providing insights into the formation and evolution of spheroid-dominated galaxies.

Findings

Strong correlation between age and sigma, consistent with observations.

Strong correlation between metallicity and sigma, matching observed trends.

Weak correlation between age and radius, aligning with empirical data.

Abstract

Recent observations have probed the formation histories of nearby elliptical galaxies by tracking correlations between the stellar population parameters, age and metallicity, and the structural parameters that enter the Fundamental Plane, radius and velocity dispersion sigma. These studies have found intriguing correlations between these four parameters. In this work, we make use of a semi-analytic model, based on halo merger trees extracted from the Bolshoi cosmological simulation, that predicts the structural properties of spheroid-dominated galaxies based on an analytic model that has been tested and calibrated against an extensive suite of hydrodynamic+N-body binary merger simulations. We predict the radius, sigma, luminosity, age, and metallicity of spheroid-dominated galaxies, enabling us to compare directly to observations. Our model predicts a strong correlation between age and sigma for early-type galaxies, and no significant correlation between age and radius, in agreement with observations. In addition we predict a strong correlation between metallicity and sigma, and a weak correlation between metallicity and radius, in qualitative agreement with observations. We find that the correlations with sigma arise as a result of the strong link between sigma and the galaxy assembly time. Minor mergers produce a large change in radius while leaving sigma nearly the same, which explains the weaker trends with radius.