The Milky Way Disc in its Extragalactic Context

We have produced updated estimates of the scale length of the Milky Way stellar disc by applying hierarchical Bayesian (HB) meta-analysis techniques to the extant literature. Our results combine 29 different photometric measurements based on a wide range of observational datasets, Milky Way models and assumptions, and methodologiesK the HB technique is robust to systematic errors that affect only a subset of measurements. In this talk, I will discuss the implications of these improved disc scale length estimates, including separate analyses of optical and infrared measurements (which prove to be consistent with each other). A key finding is that the Milky Way’s disc scale length is roughly half as large as would be expected from its luminosity (or total stellar mass) and rotation velocity, lying further from the luminosity-velocity-radius relation than roughly 90% of spirals. Tests with simulations suggest that this result could be connected to the known discrepancies between the properties of the Milky Way’s satellite population and predictions from LCDM models. Broader exploration of the links between disc properties and satellite populations in extragalactic samples may be a productive avenue for future work