NOAO >   Observing Info >   Approved Programs >   2003B-0023

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Proposal Information for 2003B-0023


PI: Deidre Hunter, Lowell Observatory, dah@lowell.edu
Address: 1400 West Mars Hill Road, Flagstaff, AZ 86001, USA

Title: The Stellar Edges of Irregular Galaxies: What's Going on Out There?

Abstract: There is considerable interest in, and ignorance of, the outer parts of galaxies. Galactic outer edges are the interaction zone between galactic and intergalactic material and are also most sensitive to galaxy-galaxy interactions. Dwarf Im galaxies, in particular, may be particularly sensitive to their external environment. In addition, I have noticed that the Holmberg radius in Im galaxies is often larger than the visible extent of star-forming regions, indicating the presence of a significant stellar population beyond where we see stars forming today. Therefore, I am proposing to continue my exploration of the stellar populations in the outer parts of nearby Im galaxies through very deep BV imaging. These data will be used to determine how far out various stellar populations extend, how the stars are distributed, and what the star formation history at the edges of irregular galaxies has been. In one Im system that I observed to (mu)_V=29 mag/arcsec^2 there were several surprises: 1) The starlight continues without an edge as far as the measurements extend, contrary to predictions of several models, 2) The radial surface brightness profile changes slope beyond R_25 and the break does not appear to correlate with any other aspect of the galaxy, and 3) the color remains constant throughout the galaxy, implying the same star formation history even to the outer parts. I want to see if these unusual features are found in other Im systems.


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NOAO >   Observing Info >   Approved Programs >   2003B-0023

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