Dr. Anna Nierenberg
University of California Chancellor's Postdoctoral Fellow 


Physics & Astronomy Department
University of California Irvine
Irvine CA 92697-2575

email: anierenb@uci.edu

Star formation in the smallest galaxies

In the most widely accepted view of the Universe, the majority of matter is ‘dark’. Collections of gas and stars form galaxies in the centers of dense regions of dark matter known as halos. This theoretical model naturally reproduces observations over a truly extraordinary range in distance, mass and time scales, from the way stars orbit in a galaxy like our own, to the way galaxies cluster on cosmic scales. Because of this success, the dark matter paradigm is widely accepted even though we have yet to directly detect dark matter.

On small scales (below the mass of the Milky Way), there are some apparent discrepancies between the simplest dark matter picture and what we observe. Notably,  simulations predict that there should be thousands of dark matter halos gravitationally bound to the Milky Way’s dark matter halo, while only a few tens of galaxies are observed. This is known as the ‘Missing Satellite Problem’.  If every dark matter halo contains a galaxy then why are there so few dark matter halos relative to what we expect around the Milky Way? Alternatively, maybe there are many small dark matter halos which do not contain enough gas or stars to be observed.

Key to resolving this discrepancy is obtaining a deeper understanding of what factors govern star formation in galaxies of small dark matter halos. This question is especially complicated at low mass scales because effects such as stellar winds and supernovae feedback have more dramatic impacts in the shallower gravitational well of small galaxies. Furthermore, small galaxies can be dramatically affected by interactions with nearby massive galaxies. I have developed new statistical and image processing methods which make it possible to measure the properties of faint galaxies at cosmological distances using space based imaging, and thus study their evolution over a significant portion of the history of the Universe (HST-AR- 3271) . This has enabled new constraints on the physics of star formation in small satellite galaxies.

Related first author papers:

Background image credit: The Magellanic Clouds By ESO/S. Brunier (ESO) [CC BY 4.0 (http://creativecommons.org/licenses/by/4.0)], via Wikimedia Commons