The star formation history of the dwarf irregular galaxy SagDIG

We present a preliminary reconstruction of the star formation history of the Sagittarius dwarf irregular galaxy (SagDIG), a dIrr galaxy at the border of the Local Group. SagDIG is a lively star-forming dwarf galaxy with very low metallicity and an abundant gas reservoir, for which deep HST ACS observations have been obtained (Momany et al. 2005). We have built synthetic color-magnitude diagrams in the intrinsic ACS bands F606W and F814W and compared them with our HST/ACS observations to derive the global star formation history of the galaxy. We find a broad episode of star formation between 3 and 8 Gyr ago, with a low-intensity tail of star formation at older ages, and a SF enhancement in the last Gyr. An upper limit to the old populations is set by modeling the old HB. Our modeling of the color-magnitude diagram also provides some constraints on the chemical enrichment history of SagDIG.