Powering a giant : using x-ray emission to determine the power source of ultraluminous infrared galaxies

Abstract

Ultraluminous Infrared Galaxies (ULIRGs) are one of the brightest sources of infrared radiation in the Universe, with luminosities upwards of 10 [superscript 12] times that of the Sun. To produce the extreme infrared luminosity found in these dusty galaxies, it is thought that they are powered by starbursts, Active Galactic Nuclei (AGN), or a combination of both. Because these galaxies contain a large amount of dust, most of the defining characteristics are obscured, making it difficult to identify the nature of the power source. High energy X-rays are able to penetrate much of the obscuring gas and dust, and potentially reveal the power source. Both AGN and starburst emission produce very specific X-ray spectra, which means that it should be possible to distinguish between the two by examining only the 0.5 to 10.0keV spectral range of specific ULIRGs. To do this, spectra between 0.5 and 10.0keV were created for a sample of eleven ULIRGs from observations made by the space-based telescope, XMM-Newton. The X-ray spectra were fitted with starburst and AGN models using the Xspec software. Most of the objects appear to be starburst driven, although a significant fraction seem to host an AGN.