Lowell Observatory Colloquia

Title: Stellar Surface Brightness Profiles of Dwarf Galaxies

Kim Herrmann, Lowell Observatory: Stellar Surface Brightness Profiles of Dwarf Galaxies

Lowell Observatory, Thursday, 09 February, 2012 at 3:30 p.m.

How does stellar light fall off with radius in disk galaxies? To zeroth order, it falls off exponentially, though theorists do not understand why it should do so. However, in the last decade it has been shown that there are three different ways for light to fall off with radius in spiral galaxies: (I) a single exponential throughout the observed region, (II) a broken exponential where the fall-off is steeper beyond the break, and (III) a broken exponential where the fall-off is shallower beyond the break. Like spirals, dwarf galaxies with stellar disks also have different profile types and even have a special case of Type II: (FI) flat or increasing inside before falling off at some break location. The reasons behind these three main profile types comprise yet another mystery. I have been re-examining an incredible sample of stellar surface brightness profiles of 141 dwarf galaxies that Deidre Hunter and collaborators have collected over more than a decade of observing in up to 11 wavelength bands: FUV and NUV from GALEX, UBVJHK and H-alpha from ground-based observations, and 3.6 and 4.5 microns from Spitzer. In this talk, I will discuss results from a human-assisted computer fitting of this data set, including: (1) statistics of break locations and other properties as a function of total galactic luminosity, wavelength, and profile type, (2) radial color trends as a function of profile type, and (3) some future work on examining the relationship of the break radius to the kinematics and density profiles of atomic hydrogen gas in the 41 dwarfs of the LITTLE THINGS subsample. I have found some intriguing trends which may shed some light on how galaxies form and evolve.

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