Infrared photometry of the inner regions of the dwarf irregular galaxy NGC 3109 ?

We present VIJHK photometry for stars in a 0.8×2.0 kpc2 inner field of the dwarf irregular galaxy NGC 3109. The infrared photometry reaches 3 magnitudes fainter than previous work. Optical and infrared color–color and color–magnitude diagrams, and a bolometric luminosity function are constructed, confirming the presence of an intermediate-age stellar population. We also present a logL/L vs logTeff diagram of the galaxy and compare the results with the theoretical isochrones of Bertelli et al. (1994) for Z = 0.004 and Y = 0.24. The comparison suggests that most of the stars detected in the IR are 109 yr or younger. We compare the infrared color–magnitude diagrams of NGC 3109 with the composite color–magnitude diagrams of LMC clusters and of the outer disk of the Scd galaxy M33. They show similar stellar content in these late–type systems.