EDGE: the mass–metallicity relation as a critical test of galaxy formation physics

Abstract

We introduce the "Engineering Dwarfs at Galaxy formation's Edge" (EDGE) project to study the cosmological formation and evolution of the smallest galaxies in the Universe. In this first paper, we explore the effects of resolution and sub-grid physics on a single low mass halo (M halo = 10 9 M ), simulated to redshift z = 0 at a mass and spatial resolution of ∼ 20 M and ∼ 3 pc. We consider different star formation prescriptions, supernova feedback strengths and on-the-fly radiative transfer (RT). We show that RT changes the mode of galactic self-regulation at this halo mass, suppressing star formation by causing the interstellar and circumgalactic gas to remain predominantly warm (∼ 10 4 K) even before cosmic reionisation. By contrast, without RT, star formation regulation occurs only through starbursts and their associated vigorous galactic outflows. In spite of this difference, the entire simulation suite (with the exception of models without any feedback) matches observed dwarf galaxy sizes, velocity dispersions, V-band magnitudes and dynamical mass-to-light-ratios. This is because such structural scaling relations are predominantly set by the host dark matter halo, with the remaining model-to-model variation being smaller than the observational scatter. We find that only the stellar mass-metallicity relation differentiates the galaxy formation models. Explosive feedback ejects more metals from the dwarf, leading to a lower metallicity at a fixed stellar mass. We conclude that the stellar mass-metallicity relation of the very smallest galaxies provides a unique constraint on galaxy formation physics.

Milky Way Satellite Census. I. The Observational Selection Function for Milky Way Satellites in DES Y3 and Pan-STARRS DR1

“…At even lower masses, the census of ultra-faint satellites is incomplete, even within the Milky Way halo. Despite significant observational challenges, the demographics of ultrafaint dwarf galaxies offer a unique window into feedback processes in galaxy formation (e.g., Mashchenko et al 2008;Wheeler et al 2015Wheeler et al , 2019Agertz et al 2020;Munshi et al 2019), reionization and the first stars (e.g., Bullock et al 2000;Shapiro et al 2004;Weisz et al 2014aWeisz et al , 2014bBoylan-Kolchin et al 2015;Ishiyama et al 2016;Weisz & Boylan-Kolchin 2017;Tollerud & Peek 2018;Graus et al 2019;Katz et al 2019), and the nature of dark matter (e.g., Bergström et al 1998;Spekkens et al 2013;Malyshev et al 2014;Ackermann et al 2015;Geringer-Sameth et al 2015;Bullock & Boylan-Kolchin 2017;Clesse & García-Bellido 2018;Nadler et al 2019a).…”

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.…”

GenetIC—A New Initial Conditions Generator to Support Genetically Modified Zoom Simulations

“…One possible way to generate a zoom simulation is to calculate the entire cosmological volume at high resolution, then degrade the sampling outside the target region. This is inefficient, however, and entirely infeasible for some applications; for example, in the EDGE suite (Rey et al 2019a;Agertz et al 2020), the initial conditions resolution corresponds to an effective grid of 32768 3 . Storing a single such grid at double precision requires 32 terabytes; manipulating it is entirely out of reach.…”