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The Populations of Carina. I. Decoding the Color-Magnitude Diagram

Accepted version
Peer-reviewed

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Article

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Authors

Norris, JE 
Yong, D 
Venn, KA 

Abstract

jats:titleAbstract</jats:title> jats:pWe investigate the color–magnitude diagram (CMD) of the Carina dwarf spheroidal galaxy using data of Stetson et al. and synthetic CMDs based on isochrones of Dotter et al., in terms of the parameters [Fe/H], age, and [jats:italicα</jats:italic>/Fe], for the cases when (i) [jats:italicα</jats:italic>/Fe] is held constant and (ii) [jats:italicα</jats:italic>/Fe] is varied. The data are well described by four basic epochs of star formation, having [Fe/H] = −1.85, −1.5, −1.2, and ∼−1.15 and ages ∼13, 7, ∼3.5, and ∼1.5 Gyr, respectively (for [jats:italicα</jats:italic>/Fe] = 0.1, constant [jats:italicα</jats:italic>/Fe], and [jats:italicα</jats:italic>/Fe] = 0.2, 0.1, −0.2, −0.2, variable [jats:italicα</jats:italic>/Fe]), with small spreads in [Fe/H] and age of order 0.1 dex and 1–3 Gyr. Within an elliptical radius 13.′1, the mass fractions of the populations, at their times of formation, were (in decreasing age order) 0.34, 0.39, 0.23, and 0.04. This formalism reproduces five observed CMD features (two distinct subgiant branches of old and intermediate-age populations, two younger, main-sequence components, and the small color dispersion on the red giant branch (RGB). The parameters of the youngest population are less certain than those of the others, and given it is less centrally concentrated, it may not be directly related to them. High-resolution spectroscopically analyzed RGB samples appear statistically incomplete compared with those selected using radial velocity, which contain bluer stars comprising ∼5%–10% of the samples. We conjecture these objects may, at least in part, be members of the youngest population. We use the CMD simulations to obtain insight into the population structure of Carina's upper RGB.</jats:p>

Description

Keywords

galaxies: abundances, galaxies: dwarf, galaxies: evolution, galaxies: individual (Carina dSph)

Journal Title

Astrophysical Journal, Supplement Series

Conference Name

Journal ISSN

0067-0049
1538-4365

Volume Title

230

Publisher

American Astronomical Society
Sponsorship
European Research Council (320360)