A new infrared view of evolved stars in IZw 18
Abstract
We report results from near-infrared imaging of IZw 18, the most metal-poor galaxy in the local universe, with NICMOS on board the Hubble Space Telescope (HST). Observations were obtained in the broad F205W filter (~K) and in the medium-wide bands F171M and F180M, the latter which cover strong molecular absorption features in cool stars. The new data, together with previously obtained HST/NICMOS images in the F110W (~J) and F160W (~H) filters, provide a census of the cool stellar population in this chemically unevolved galaxy. We find that stars as old as ~1 Gyr are required to explain the observed colour-magnitude diagrams. Combining broad and medium-wide band photometry, we have classified the observed stars. The observed stellar populations, to the depth of our data, are dominated by luminous red supergiant stars. However, an intermediate-age component is also present. We have identified carbon star candidates, and show that they dominate the stellar content for intermediate mass and age. We show that low metallicity intermediate-age stars have, for a given colour, a F110W (~J-band) excess compared to local carbon stars. The carbon stars identified in IZw 18 are the most distant (more than 10 Mpc) resolved examples yet discovered.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- April 2005
- DOI:
- 10.1051/0004-6361:20041172
- arXiv:
- arXiv:astro-ph/0411217
- Bibcode:
- 2005A&A...433..797O
- Keywords:
-
- galaxies: dwarf;
- galaxies: stellar content;
- galaxies: individual: <ASTROBJ>IZw18</ASTROBJ>;
- stars: carbon;
- stars: AGB and post-AGB;
- Astrophysics
- E-Print:
- Accepted for publication in A&