The Chandra Deep Field–North Survey. XI. X-Ray Emission from Luminous Infrared Starburst Galaxies

Abstract

Using the 1 Ms Chandra Deep Field-North and 15 μm ISOCAM Hubble Deep Field-North surveys, we find a tight correlation between the population of strongly evolving starburst galaxiess discovered in faint 15 μm ISOCAM surveys and the apparently normal galaxy population detected in deep X-ray surveys. Up to 100% of the X-ray-detected emission-line galaxies (ELGs) have 15 μm counterparts, in contrast to 10%-20% of the X-ray-detected absorption-line galaxies and AGN-dominated sources. None of the X-ray-detected ELGs are detected in the hard band (2-8 keV), and their stacked-average X-ray spectral slope of Γ ≈ 2.0 suggests a low fraction of obscured AGN activity within the X-ray-detected ELG population. The characteristics of the z = 0.4-1.3 X-ray-detected ELGs are consistent with those expected for M82- and NGC 3256-type starburst galaxies; these X-ray-detected ELGs contribute ≈2% of the 0.5-8.0 keV extragalactic X-ray background. The only statistical difference between the X-ray-detected and X-ray-undetected 15 μm-selected ELGs is that a much larger fraction of the former have radio emission.