Stellar populations in NGC 5128 with the VLT: Evidence for recent star formation

Abstract

We resolve stars of the nearest giant elliptical galaxy NGC 5128 using VLT with FORS1 and ISAAC. We construct deep U, V and K_s color-magnitude and color-color diagrams in two different halo fields (in the halo and in the north-eastern diffuse shell). In the outer, shell field, at ~ 14 kpc from the center of the galaxy, there is a significant recent star formation with stars as young as 10 Myr, approximately aligned with the prominent radio and X-ray jet from the nucleus of the host AGN. Ionized gas filaments are evident in ultraviolet images near the area where neutral HI and CO molecular gas was previously observed. The underlying stellar population of the halo of the giant elliptical is predominantly old with a very broad metallicity distribution. The presence of an extended giant branch reaching M_bol=-5 mag suggests the existence of a significant intermediate-age AGB population in the halo of this galaxy. Based on observations collected at the European Southern Observatory, Paranal, Chile, within the Observing Programmes 63.N-0229 and 65.N-0164, and in part on observations collected by the NASA/ESA Hubble Space Telescope, which is operated by AURA, Inc., under NASA contract NAS5-26555.