Published in The Astronomy and Astrophysics Review, Volume 18, Issue 1-2, pp. 1-65, 2010.
astro-ph/0909.4234

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Abstract. In this tutorial paper we summarize how the star formation (SF) history of a galactic region can be derived from the colour-magnitude diagram (CMD) of its resolved stars. The procedures to build synthetic CMDs and to exploit them to derive the SF histories (SFHs) are described, as well as the corresponding uncertainties. The SFHs of resolved dwarf galaxies of all morphological types, obtained from the application of the synthetic CMD method, are reviewed and discussed. In short: 1) Only early-type galaxies show evidence of long interruptions in the SF activity; late-type dwarfs present rather continuous, or gasping, SF regimes; 2) A few early-type dwarfs have experienced only one episode of SF activity concentrated at the earliest epochs, whilst many others show extended or recurrent SF activity; 3) No galaxy experiencing now its first SF episode has been found yet; 4) No frequent evidence of strong SF bursts is found; 5) There is no significant difference in the SFH of dwarf irregulars and blue compact dwarfs, except for the current SF rates. Implications of these results on the galaxy formation scenarios are briefly discussed.

Keywords: Galaxies: dwarfs - Galaxies: evolution - Galaxies: stellar content

Table of Contents

• INTRODUCTION
• STAR FORMATION HISTORIES FROM COLOUR-MAGNITUDE DIAGRAMS: THE METHOD
• Building a synthetic population
• Stellar ages from a CMD
• Deep is better
• DEDUCING THE SFH: GUIDELINES
• A changing landscape
• To grid or not to grid
• Maximum Likelihood
• Wondering in the parameter space
• A practical example
• Uncertainties affecting the synthetic CMD procedures
• Completeness
• IMF
• Binaries
• Metallicity and metallicity spread
• Helium content
• Reddening and distance
• Additional issues
• STAR FORMATION HISTORIES OF RESOLVED DWARFS FROM SYNTHETIC CMD ANALYSES: RESULTS
• CONCLUDING REMARKS
• REFERENCES