TSI Seminar

Microgalaxies, or, how low can we go?

Alan McConnachie

NRC HIA / University of Victoria

Every year for the past 20 years or so, there have been new additions to the extreme low luminosity end of the galaxy luminosity function, and the record for the lowest luminosity system known has been continually broken. This regime is fascinating for investigations relating to galaxy formation, galaxy dynamics and dark matter halos. In many respects, the smallest dwarfs are an excellent stress test for cosmology given that the modern cosmological paradigm was developed with most consideration given to the largest, not smallest, scales. As such, the identification earlier this year of UNIONS1/Ursa Major 3, a potential dwarf galaxy with a stellar mass of only approximately 16 Msun, is a landmark, if somewhat bizarre, discovery. Its existence raises some very basic questions, such as how such a low a luminosity system (and how low mass a dark matter halo) can form and survive? I will discuss the discovery of this and related objects, and results from follow up observations including using some new instrumentation developed here in Canada. Given there are likely only about 60 stars in UNIONS 1 above the hydrogen burning limit, I will also address the observational elephant in the room, namely, where do we go from here?