Exploring simulated early star formation in the context of the ultrafaint dwarf galaxies

Abstract

Ultrafaint dwarf galaxies (UFDs) are typically assumed to have simple, stellar populations with star formation ending at reionization. Yet as the observations of these galaxies continue to improve, their star formation histories (SFHs) are revealed to be more complicated than previously thought. In this paper, we study how star formation, chemical enrichment, and mixing proceed in small, dark matter halos at early times using a high-resolution, cosmological, hydrodynamical simulation. The goals are to inform the future use of analytic models and to explore observable properties of the simulated halos in the context of UFD data. Specifically, we look at analytic approaches that might inform metal enrichment within and beyond small galaxies in the early Universe. We find that simple assumptions for modeling the extent of supernova-driven winds agree with the simulation on average whereas inhomogeneous mixing and gas flows have a large effect on the spread in simulated stellar metallicities. In the context of the UFDs, this work demonstrates that simulations can form halos with a complex SFH and a large spread in the metallicity distribution function within a few hundred Myr in the early Universe. In particular, bursty and continuous star formation are seen in the simulation and both scenarios have been argued from the data. Spreads in the simulated metallicities, however remain too narrow and too metal-rich when compared to the UFDs. Future work is needed to help reduce these discrepancies and advance our interpretation of the data.

Exploring chemical homogeneity in dwarf galaxies: a VLT-MUSE study of JKB 18

“…Recent works have begun to include sufficient, detailed physics to capture metal mixing in dwarf galaxies (e.g Shen, Wadsley & Stinson 2010;Few et al 2012;Shen et al 2013;Brook et al 2014 Su et al 2017;Corlies, Johnston & Wise 2018;Côté et al 2018;Escala et al 2018). But these works generally focus on stellar metallicity distributions as opposed to the type gas-phase distributions studied for JKB18.…”

The little things matter: relating the abundance of ultrafaint satellites to the hosts’ assembly history

“…The stellar masses of the ultrafaint satellites are so small that they are beyond the reach of the current generation of cosmological hydrodynamical simulations, such as A (Sawala et al 2016;Fattahi et al 2016), A (Grand et al 2017) or F (Hopkins et al 2014(Hopkins et al , 2018, which, at best, have a stellar mass resolution of ★ ∼ 10 3 −10 4 M , although higher resolution may be achieved in simulations of isolated dwarf galaxies (e.g. Read et al 2016;Jeon et al 2017;Corlies et al 2018;Wheeler et al 2018;Munshi et al 2019;Rey et al 2019;Agertz et al 2020). Instead, we use the technique of semi-analytic galaxy modelling in which mass resolution is not an issue.…”

Dancing in the Dark: Uncertainty in Ultrafaint Dwarf Galaxy Predictions from Cosmological Simulations

“…The lowest mass galaxy yet observed contains only a few hundred M ⊙ in stars (Homma et al 2018). To understand these extremely low mass systems, a few authors have simulated the formation of isolated UFD galaxies at high resolution (Read et al 2016;Jeon et al 2017;Corlies et al 2018). Some cosmological simulations of classical dwarf galaxies have been able to resolve the formation of UFD satellite companions Wheeler et al (2015Wheeler et al ( , 2018; Munshi et al (2017).…”