Deconstructing NGC 7130

Abstract

Observations of the Seyfert 2 and starburst galaxy NGC 7130 with the Chandra X-Ray Observatory illustrate that both of these phenomena contribute significantly to the galaxy's detectable X-ray emission. The active galactic nucleus (AGN) is strongly obscured, buried beneath column density N_H>10²⁴cm^-2, and it is most evident in a prominent Fe Kα emission line with equivalent width greater than 1 keV. The AGN accounts for most (60%) of the observed X-rays at energy E>2 keV, with the remainder due to spatially extended star formation. The soft X-ray emission is strong and predominantly thermal on both small and large scales. We attribute the thermal emission to stellar processes. In total, the AGN is responsible for only one-third of the observed 0.5-10 keV luminosity of 3×10⁴¹ergss^-1 of this galaxy and less than half of its bolometric luminosity. Starburst/AGN composite galaxies like NGC 7130 are truly common, and similar examples may contribute significantly to the high-energy cosmic X-ray background while remaining hidden at lower energies, especially if they are distant.