Presentation #427.06 in the session “Black Holes”.
Binary population synthesis models suggest that X-ray emission from star-forming galaxies, consisting primarily of emission from X-ray binaries (XRBs) and the hot interstellar medium (ISM), will be the dominant source of high-energy photons at high redshift. Cosmological models further suggest that in the early Universe X-ray emission from the first galaxies will be a critical source of heating for the intergalactic medium. However, a key uncertainty in these models is the form of the X-ray SED for high redshift galaxies. To date, studies of X-ray SEDs have focused largely on local, star-forming galaxies at solar metallicity, where the properties of the ISM and XRB population may be quite different from those of the first galaxies, which are expected to be relatively metal-free. Using a combination of Chandra, XMM-Newton, and NuSTAR observations, we present new constraints on the 0.3-30 keV SED of the low-metallicity starburst galaxy VV 114. We find the X-ray SED of VV 114 is dominated by emission from ultra-luminous X-ray sources at energies greater than 1.5 keV, and has an elevated galaxy-integrated X-ray luminosity per unit star formation rate relative to higher-metallicity star-forming galaxies. We discuss our results in terms of the effect of metallicity on XRB populations and emission from the hot ISM, and the importance of X-ray emission from star-forming galaxies in the early Universe.