A low pre-infall mass for the Carina dwarf galaxy from disequilibrium modelling

TL;DR

This paper estimates a very low pre-infall dark matter halo mass for the Carina dwarf galaxy using disequilibrium modelling, challenging standard galaxy formation models and suggesting the existence of many dark, starless dwarf halos around the Milky Way.

Contribution

It introduces a novel disequilibrium modelling approach to determine the pre-infall mass of Carina, revealing lower masses than predicted by cosmological simulations.

Findings

Carina's pre-infall halo mass is approximately 360 million solar masses.

Standard models require stochastic galaxy formation below 10 billion solar masses.

A significant population of dark, starless dwarf halos may exist around the Milky Way.

Abstract

Dark matter only simulations of galaxy formation predict many more subhalos around a Milky Way like galaxy than the number of observed satellites. Proposed solutions require the satellites to inhabit dark matter halos with masses between one to ten billion solar masses at the time they fell into the Milky Way. Here we use a modelling approach, independent of cosmological simulations, to obtain a preinfall mass of 360 (+380,-230) million solar masses for one of the Milky Way's satellites: Carina. This determination of a low halo mass for Carina can be accommodated within the standard model only if galaxy formation becomes stochastic in halos below ten billion solar masses. Otherwise Carina, the eighth most luminous Milky Way dwarf, would be expected to inhabit a significantly more massive halo. The implication of this is that a population of "dark dwarfs" should orbit the Milky Way: halos devoid of stars and yet more massive than many of their visible counterparts.