Estimating the evolution of gas in the Fornax dwarf spheroidal galaxy from its star formation history: an illustrative example

TL;DR

This paper demonstrates how star formation history data can be used to estimate the evolution of gas and total mass in dwarf spheroidal galaxies, exemplified by the Fornax galaxy, revealing insights into its gas flow and halo growth.

Contribution

It introduces a method to infer gas evolution in dSphs from star formation history, applying it to Fornax and estimating its halo growth and gas flow transition.

Findings

Fornax's halo grew to ~2x10^9 M_sun at t_sat ~ 5-8 Gyr

Transition from gas inflow to outflow identified at t_sat

Estimated halo growth aligns with previous kinematic studies

Abstract

We propose that detailed data on the star formation history of a dwarf spheroidal galaxy (dSph) may be used to estimate the evolution of the total mass M_g(t) for cold gas in its star-forming disk. Using Fornax as an illustrative example, we estimate its M_g(t) and the corresponding net gas flow rate Delta F(t) assuming a global star formation rate psi(t) = lambda_*(t)[M_g(t)/M_sun]^alpha consistent with observations of nearby galaxies. We identify the onset of the transition in Delta F(t) from a net inflow to a net outflow as the time t_sat at which the Fornax halo became a Milky Way satellite and estimate the evolution of its total mass M_h(t) at t < t_sat using the median halo growth history in the LambdaCDM cosmology and its present mass within the half-light radius derived from observations. We examine three different cases of alpha = 1, 1.5, and 2, and justify the corresponding lambda_*(t) by comparing the gas mass fraction f_g(t) = M_g(t)/M_h(t) at t < t_sat with results from simulations of gas accretion by halos in a reionized universe. We find that the Fornax halo grew to M_h(t_sat) ~ 2x10^9 M_sun at t_sat ~ 5 or 8 Gyr, in broad agreement with previous studies using data on its stellar kinematics and its orbital motion. We describe qualitatively the evolution of Fornax as a satellite and discuss potential extension of our approach to other dSphs.