The distance to the C component of I Zw 18 and its star formation
  history: A probabilistic approach
  We analyzed the resolved stellar population of the C component of the
extremely metal-poor dwarf galaxy Izw18 in order to evaluate its distance and
star formation history as accurately as possible. In particular, we aimed at
answering the question of whether this stellar population is young. We
developed a probabilistic approach to analyzing high-quality photometric data
obtained with the Advanced Camera for Surveys of the Hubble Space Telescope.
This approach gives a detailed account of the various stochastic aspects of
star formation. We carried out two successive models of the stellar population
of interest, paying attention to how our assumptions could affect the results.
We found a distance to the C component of I Zw 18 as high as 27 Mpc, a
significantly higher value than those cited in previous works. The star
formation history we inferred from the observational data shows various
interesting features: a strong starburst that lasted for about 15 Myr, a more
moderate one that occurred approx 100 Myr ago, a continuous process of star
formation between both starbursts, and a possible episode of low level star
formation at ages over 100 Myr. The stellar population studied is likely approx
125 Myr old, although ages of a few Gyr cannot be ruled out. Furthermore,
nearly all the stars were formed in the last few hundreds of Myr.
