Testing the Nature of Ultraluminous X-ray Sources with Spitzer and Determining their Impact on their Immediate Environment

Based on our discovery that ultraluminous X-ray sources (ULX sources) in galaxies can impact their surroundings and thus produce key diagnostic IR spectral signatures, we propose IRS mapping observations of six ULX sources with Spitzer. These are chosen from established X-ray catalogs and have optical evidence for extended nebula or 'bubbles' or are located in regions near star formation. With these data, we will map key mid-IR diagnostic emission lines, such as [O IV] to measure the impact of a hard X/UV ionizing source. One of the only constraints on the emission geometry of ULX sources is set by observations of the ionization mechanism of the nebula with symmetric geometry that surround many of them. These nebula are very anamalous, being larger and more luminous than normal SNR and showing higher ionization than HII regions, and are likely photoionized by the ULX source. With our Spitzer observations, we will estimate the luminosity of the central object in the ionizing UV band in a geometry independent manner and test whether these sources are as luminous as the X-ray data would indicate, thus testing beaming models for the X-ray emission.