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Deep Hubble Space Telescope Imaging of Sextans A. III. The Star Formation History
Citation
Dolphin, AE and Saha, A and Skillman, ED and Dohm-Palmer, RC and Tolstoy, E and Cole, AA and Gallagher, JS and Hoessel, JG and Mateo, M, Deep Hubble Space Telescope Imaging of Sextans A. III. The Star Formation History, The Astronomical Journal, 126, (1) pp. 187-196. ISSN 0004-6256 (2003) [Refereed Article]
DOI: doi:10.1086/375761
Abstract
We present a measurement of the star formation history of Sextans A, based on WFPC2 photometry that is 50% complete to V = 27.5 (MV ∼ +1.9) and I = 27.0. The star formation history and chemical enrichment history have been measured through modeling of the color-magnitude diagram (CMD). We find evidence for increased reddening in the youngest stellar populations and an intrinsic metallicity spread at all ages. Sextans A has been actively forming stars at a high rate for ∼2.5 Gyr ago, with an increased rate beginning ∼0.1 Gyr ago. We find a nonzero number of stars older than 2.5 Gyr, but because of the limited depth of the photometry, a detailed star formation history at intermediate and older ages has considerable uncertainties. The mean metallicity was found to be [M/H] ≈ -1.4 over the measured history of the galaxy, with most of the enrichment happening at ages of at least 10 Gyr. We also find that an rms metallicity spread of 0.15 dex at all ages allows the best fits to the observed CMD. We revisit our determination of the recent star formation history (age ≤ 0.7 Gyr) using blue helium-burning (BHeB) stars and find good agreement for all but the last 25 Myr, a discrepancy resulting primarily from different distances used in the two analyses and the differential extinction in the youngest populations. This indicates that star formation histories determined solely from BHeB stars should be confined to CMD regions where no contamination from reddened main-sequence stars is present.
Item Details
Item Type: | Refereed Article |
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Research Division: | Physical Sciences |
Research Group: | Astronomical sciences |
Research Field: | Galactic astronomy |
Objective Division: | Expanding Knowledge |
Objective Group: | Expanding knowledge |
Objective Field: | Expanding knowledge in the physical sciences |
UTAS Author: | Cole, AA (Associate Professor Andrew Cole) |
ID Code: | 45315 |
Year Published: | 2003 |
Web of Science® Times Cited: | 62 |
Deposited By: | Physics |
Deposited On: | 2007-07-10 |
Last Modified: | 2007-07-10 |
Downloads: | 0 |
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