Extragalactic archeology in integrated light: A test case with NGC 4030

Abstract

We reconstruct the age-velocity distribution of the central region of the Sbc galaxy NGC4030, by applying STECKMAP to very high quality WHT/ISIS data. We find that the main component is a relatively young (≈ 2 Gyr) bulge with a ≈ 100 km/s velocity dispersion. The best fit solution also shows a superimposed young, kinematically cold (σ_{v}∼ 30 km/s) component. Monte-Carlo simulations show that the detection of this component is robust given the observational setup and quality of the data, and that it is not likely to be an artifact of the inversion procedure. We propose that this component is actually a young stellar disk, seen superimposed on the bulge. This demonstrates the feasibility of separating superimposed stellar components and measuring their age and kinematics in integrated light, thereby confirming the results of Ocvirk et al. (2006b), but this time with real data. This is an important success for our tool in a series of tests and towards new results in extragalactic archeology.