Computational issues in chemo-dynamical modelling of the formation and evolution of galaxies

Abstract

Chemo-dynamical N-body simulations are an essential tool for understanding the formation and evolution of galaxies. As the number of observationally determined stellar abundances continues to climb, these simulations are able to provide new constraints on the early star formaton history and chemical evolution inside both the Milky Way and Local Group dwarf galaxies. Here, we aim to reproduce the low α-element scatter observed in metal-poor stars. We first demonstrate that as stellar particles inside simulations drop below a mass threshold, increases in the resolution produce an unacceptably large scatter as one particle is no longer a good approximation of an entire stellar population. This threshold occurs at around 10 3 M , a mass limit easily reached in current (and future) simulations. By simulating the Sextans and Fornax dwarf spheroidal galaxies we show that this increase in scatter at high resolutions arises from stochastic supernovae explosions. In order to reduce this scatter down to the observed value, we show the necessity of introducing a metal mixing scheme into particle-based simulations. The impact of the method used to inject the metals into the surrounding gas is also discussed. We finally summarise the best approach for accurately reproducing the scatter in simulations of both Local Group dwarf galaxies and in the Milky Way.

Connecting the First Galaxies with Ultrafaint Dwarfs in the Local Group: Chemical Signatures of Population III Stars

“…However, these works only followed the chemical evolution of total metallicity, rather than individual metal species, and none tracked the metal enrichment history from Population III stars to low redshift. Furthermore, existing work concerning the chemical abundances is typically considered in an idealized setting (e.g., Revaz et al 2009;Corlies et al 2013;Webster et al 2014;Bland-Hawthorn et al 2015;Webster et al 2015;Revaz et al 2016). As such, the connection of the stellar populations of LG UFDs and low-mass dwarfs to those of the first generation of stars remains uncertain.…”

Efficiency of Metal Mixing in Dwarf Galaxies

“…Their results suggest that metal diffusion increases the metal content of gas in galaxies and decrease it in the intergalactic medium. Revaz et al (2016) systematically studied the scatters of α-elements with different parameters. They show that metal mixing is required to reduce the scatters of α-elements in particle-based simulations.…”

“…Williamson et al (2016) However, the efficiency of metal mixing is not yet understood. Revaz et al (2016) pointed out that the scaling factor for their metal diffusion of 10 −3 reproduce the low scatters of α-elements in dSphs, but more efficient mixing is required to reproduce that of a Milky Way-like galaxy. Low scatters of α-elements (∼ 0.2 dex) make it difficult to constrain the efficiency of metal mixing.…”

The Impact of Modeling Assumptions in Galactic Chemical Evolution Models

“…On the other hand, outflows remove metals from galaxies and tend to slow down the growth of their metal content at later time. These ingredients are usually included in the simulation of dwarf galaxies, but with different levels of complexity and different numerical methods, including one-zone models (e.g., Carigi et al 2002;Lanfranchi & Matteucci 2003, 2004Fenner et al 2006;Gibson 2007;Lanfranchi & Matteucci 2010;Lanfranchi et al 2006;Vincenzo et al 2014;Homma et al 2015;Kobayashi et al 2015;Ural et al 2015a), semi-analytical models (e.g., Romano & Starkenburg 2013;Romano et al 2015), and hydrodynamical simulations (e.g., Kawata et al 2006;Marcolini et al 2008;Revaz et al 2009;Pilkington et al 2012;Revaz & Jablonka 2012;Hirai et al 2015;Revaz et al 2016).…”