Satellite mass functions and the faint end of the galaxy mass-halo mass relation in LCDM

Abstract

The abundance of the faintest galaxies provides insight into the nature of dark matter and the process of dwarf galaxy formation. In the LCDM scenario, low mass halos are so numerous that the efficiency of dwarf formation must decline sharply with decreasing halo mass in order to accommodate the relative scarcity of observed dwarfs and satellites in the Local Group. The nature of this decline contains important clues to the mechanisms regulating the onset of galaxy formation in the faintest systems. We explore here two possible models for the stellar mass (M * )-halo mass (M 200 ) relation at the faint end, motivated by some of the latest LCDM cosmological hydrodynamical simulations. One model includes a sharp mass threshold below which no luminous galaxies form, as expected if galaxy formation proceeds only in systems above the Hydrogen-cooling limit. In the second model, M * scales as a steep power-law of M 200 with no explicit cutoff, as suggested by recent semianalytic work. Although both models predict satellite numbers around Milky Way-like galaxies consistent with current observations, they predict vastly different numbers of ultra-faint dwarfs and of satellites around isolated dwarf galaxies. Our results illustrate how the satellite mass function around dwarfs may be used to probe the M * -M 200 relation at the faint end and to elucidate the mechanisms that determine which low-mass halos "light up" or remain dark in the LCDM scenario.

Snowmass2021 Cosmic Frontier White Paper: Dark Matter Physics from Halo Measurements

“…In parallel, semi-analytic and empirical galaxy-halo connection models have been combined with observations to infer ultra-faints' halo properties; in these models, the number of observable ultra-faints suggests that these systems occupy halos with masses down to ∼ 10 8 M (near the "atomic cooling limit"; [436,437,449,450]) or even lower [451,452]. The fraction of low-mass halos that host UFDs and the scatter in the stellar mass-halo mass relation for these systems are also being studied in order to precisely characterize the properties of halos near the galaxy formation threshold [453][454][455][456].…”

Galactic tides and the Crater II dwarf spheroidal: a challenge to LCDM?

“…This profile is fully specified by two parameters; e.g., a virial mass, 𝑀 200 , and concentration, 𝑐 = 𝑟 200 /𝑟 𝑠 , or, alternatively, by a maximum circular velocity, 𝑉 max , and the radius at which it is reached, 𝑟 max . Cosmological hydrodynamical simulations, such as the APOSTLE suite of Local Group simulations (Sawala et al 2016;Fattahi et al 2016), have shown that 𝑉 max correlates strongly with galaxy stellar mass, 𝑀 ★ (see also Santos-Santos et al 2021, for a recent compilation). We adopt a stellar mass for Crater II of 𝑀 ★ = 2.56 × 10 5 M , computed from the absolute magnitude of Torrealba et al (2016) and assuming 𝑀 ★ /𝐿 𝑉 = 1.6, typical of dwarf galaxies in the Local Group (Woo et al 2008).…”

Around the Spindle Galaxy: The Dark Halo Mass of NGC 3115

“…The dimensionless quantity M T /M * characterizes the history of star formation in the galaxy, as well as its present dynamic status. In recent years, many publications have appeared in which the magnitude of M T /M * is modeled depending on the luminosity or mass of the galaxy (Moster et al 2013;Sales et al 2013;Wechsler & Tinker 2018;Santos-Santos et al 2021). As shown by theoretical calculations and observational results, the minimum ratio M T /M * occurs for galaxies of the Milky Way type with M * /M e ∼ 11 dex, increasing both toward more massive galaxies and toward dwarf systems (Kourkchi & Tully 2017;Lapi et al 2018;Posti & Fall 2021).…”