Variations in Star Formation History and the Red Giant Branch Tip
Abstract
We examine the reliability of the tip of the red giant branch (TRGB) as a distance indicator for stellar populations with different star formation histories (SFHs) when photometric errors and completeness corrections at the TRGB are small. In general, the TRGB-distance method is insensitive to the shape of the SFH except when it produces a stellar population with a significant component undergoing the red giant branch phase transition. The I-band absolute magnitude of the TRGB for the middle and late stages of this transition (~1.3-1.7 Gyr) is several tenths of a magnitude fainter than the canonical value of MI~-4.0. If more than ~30% of all stars formed over the lifetime of the universe are formed at these ages, then the distance could be overestimated by ~10%-25%. Similarly, the TRGB-distance method is insensitive to the metallicity distribution of stars formed except when the average metallicity is greater than <[Fe/H]>=-0.3. If more than ~70% of all stars formed have [Fe/H]>-0.3, the distance could be overestimated by ~10%-45%. We find that two observable quantities, the height of the discontinuity in the luminosity function at the TRGB and the median (V-I)0 at MI=-3.5, can be used to test whether the aforementioned age and metallicity conditions are met.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 2004
- DOI:
- 10.1086/383026
- arXiv:
- arXiv:astro-ph/0401387
- Bibcode:
- 2004ApJ...606..869B
- Keywords:
-
- Galaxies: Distances and Redshifts;
- Galaxies: Dwarf;
- Galaxies: Stellar Content;
- Galaxies: Local Group;
- Astrophysics
- E-Print:
- 41 pages, 30 figures, uses emulateapj5.sty, accepted to ApJS, high resolution figures available at http://www.astro.ufl.edu/~mbarker/trgb_figs