M. Tosi on IZw18
The full title of the last of today's talk is Izw18, or the Picture of Dorian Gray: the more you watch it, the older it gets. This is again about the object mentioned in the last talk (and blog entry) and discusses the case of the best candidate of a "young galaxy" in the local universe, and thereby being a counterpart of what has happened earlier in the universe.
A possible explanation of the low metallicity of the interstellar gas is that winds from supernovae blow out the metal-enriched gas and thus rid IZw18 of the metals it has produced.
There are AGB-stars detected in Izw18 (partly by my supervisor G. Östlin) and therefore the age must be at least 500 Myr. In addition, other groups (Momany 2005) have found an RGB and thus lifting the age to 2 Gyr.
Tentative results by Tosi calibrate the distance to IZw18 more accurately, thereby fixing the y-axis of the HR-diagram and determining if it is AGB or RGB stars one has found. It seems that indeed stars with an age of 1.7Gyr or older have been found.