WFPC2 Observations of the Carina Dwarf Spheroidal Galaxy

Astronomy and Astrophysics – Astronomy

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Scientific paper

We present our analysis of {Hubble Space Telescope} Wide Field Planetary Camera 2 observations in F555W ( ~ V) and F814W ( ~ I) of the Carina dwarf spheroidal galaxy. The resulting V vs V-I color-magnitude diagrams reach V=27.0 mag. A new estimate of the distance modulus of Carina, (m-M)_0({) } = 19.87+/-0.11 mag, has been derived from existing photometry in the literature. The apparent distance moduli in V and I were determined to be (m-M)_V({) } = 20.05+/-0.11 mag and (m-M)_I({) } = 19.98+/-0.12 mag, respectively. The reddening of Carina is estimated to be E(V-I)=0.08+/-0.02 mag. These determinations assumed that Carina has a metallicity of {[Fe/H]}=-1.9+/-0.2 dex. These WFPC2 observations indicate that the star formation history of the central region of Carina dwarf spheroidal galaxy was different than that found in the outer regions of the galaxy. Stars formed continuously in the central region of Carina for at least 11 Gyr. Star formation began about gtrsim 15 Gyr ago and ended about 4 Gyr ago. The rate of star formation appears to have been negligible during the last few billions years. No evidence was found for a period of quiescent star formation between the old stellar population and the dominant intermediate-age stellar population that was seen in previous studies based primarily on observations of the outer regions of the galaxy. The process of star formation in the central region of Carina may have been punctuated by short periods of enhanced star formation at approximately 5.5+/-0.5 and 8.0+/-0.8 Gyr ago. This observation provides evidence that at least some dwarf galaxies can have complex global star formation histories with local variations of the rate of star formation as a function of time and position within the galaxy.

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