MeerKAT and the smallest galaxies

Abstract

On small scales, there exists a tension between observations of dwarf galaxies and predictions for low-mass dark matter halos from simulations (often referred to as the small scale crisis). This tension includes a mismatch in number count (e.g., the canonical "missing satellites problem") but also discrepancies in the internal structure (e.g., the "too big too fail" problem). More recently, observations have revealed that low-mass satellite galaxies appear to form structures around their central galaxy ("planes of satellites") while these structures are not predicted in cosmological simulations. Detailed observations of low mass galaxies are critical for constraining the baryonic feedback processes that are used to alleviate these discrepancies. A particularly fruitful course is to study dwarf galaxies that have a substantial reservoir of neutral hydrogen (H I). These are the systems that are the most likely to be isolated, helping to disentangle intrinsic properties from evolutionary effects, and H I kinematics can offer an immediate constraint on the hosting dark matter halo. Given MeerKAT’s exquisite sensitivity, it can potentially contribute to these studies of low-mass H I-rich dwarf galaxies that will help resolve the small scale crisis. The current large H I surveys are not designed for these studies, but will still manage to detect a sample of galaxies with H I masses below 107 M comparable to the number of systems currently in the literature, and will resolve ∼15 systems with masses below 108.5 M, a critical regime for addressing which dark matter halos host low-mass galaxies. We propose a thousand hour survey of the Centaurus region, encompassing the M 83 and Cen A galaxy groups, which can robustly address key questions in understanding low-mass galaxies. The central question to be addressed is: "How many galaxies equivalent to Leo T are there in the Centaurus region?" Leo T is the lowest mass, gas-rich galaxy currently known; our proposed survey is designed to be able to detect an object of similar H I mass and linewidth throughout the volume of the Centuaurus region, which will provide a full census of how many objects like this there are in a typical galaxy group. In addition, planes of satellites have recently been identified around Cen A and our survey will be able to address how far out these planes extend: are they structures concentrated only around the central galaxy or are they connected to large scale structure?