Are There Young Galaxies in the Local Universe: The Age of Blue Compact Dwarf Galaxy I Zw 18
Trinh X Thuan
Department of Astronomy
We shall obtain deep V and I images of the most metal-deficient star-forming galaxy known, the blue compact dwarf (BCD)
I Zw 18, which has only 2% of the sun's metallicity. The aim is to put constraints on the age of the BCD by resolving the stellar content of the galaxy, and detecting or putting limits on the red giant branch (RGB) stellar population in I Zw 18 : does its very low metallicity mean that it is primordial, i.e. is the BCD forming stars now for the first
time? We will perform stellar photometry to a limit of V ~ 28 mag and I ~ 27 mag. We will use the DAOPHOT package in IRAF for point-spread function (PSF) fitting photometry. We will carry out completeness analysis by adding artificial
stars using the DAOPHOT routine ADDSTAR and checking how many are recovered by our procedure. NN 'e will then construct I versus (V-I) color-magnitude diagrams of stars in various regions of I Zw 18 (in particular the NW, SE and C components) and compare with theoretical stellar evolutionary tracks to derive ages. If RGB stars are not detected, then we can set an upper limit for the age of I Zw 18 to be less than ~ 1 Gyr. If they are detected, I Zw 18 is not young, and the RGB tip can be used to derive its distance and set limits on the metallicity of the pregalactic gas.
More information at www.astro.virginia.edu
Project Sponsored By: Space Telescope Science Institute
Start Date: 5/1/2003
- End Date: 12/31/2008
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