Starburst-AGN mixing - I. NGC 7130

We present an integral field spectroscopic study of the luminous infrared galaxy NGC 7130, a known starburst-active galactic nucleus (AGN) composite galaxy. We employ standard emission-line ratio diagnostics and maps of velocity dispersion and velocity field to investigate how the dominant ionizing sources change as a function of radius. From the signatures of both star formation and AGN activity we show that NGC 7130 is a remarkably clean case of starburst-AGN mixing. We find a smooth transition from AGN-dominated emission in the centre to pure star-forming activity further out, from which we can estimate the radius of the extended narrow line region to be 1.8 ± 0.8 kpc. We calculate that the fraction of [O III] luminosity due to star formation and AGN activity is 30 ± 2 and 70 ± 3 per cent, respectively, and that the fraction of Hα luminosity due to star formation and AGN activity is 65 ± 3 and 35 ± 2 per cent, respectively. We conclude with a discussion of the importance and potential of starburst-AGN mixing for future studies of the starburst-AGN connection.