New HST/ACS Data of the Starburst Irregular Galaxy NGC 4449

We present B, V and I photometry with HST/ACS of the resolved stellar populations in the Magellanic starburst galaxy NGC 4449. Our photometry provides ≈ 300,000 objects in the (B, V) color-magnitude diagrams (CMDs) and ≈ 400,000 objects in the (V, I) CMDs. The features observed in the CMDs imply a variety of stellar ages up to at least 1 Gyr, and possibly as old as a Hubble time. Our data clearly indicate the presence of an age gradient, with young and intermediate-age stars concentrated toward the galactic center, and old stars present everywhere. We derive the distance of NGC 4449 with an accuracy of 5% from the tip of the red giant branch: D = 3.82 ± 0.18 Mpc.