2010ApJ...724..559L

We present new Chandra observations that complete a sample of seventeen (17) luminous infrared galaxies (LIRGs) with D < 60 Mpc and low Galactic column densities of N_H≲ 5x10²⁰/cm2. The LIRGs in our sample have total infrared (8-1000 µm) luminosities in the range of L_IR~ (1-8)x10¹¹ L_☉. The high-resolution imaging and X-ray spectral information from our Chandra observations allow us to measure separately X-ray contributions from active galactic nuclei and normal galaxy processes (e.g., X-ray binaries and hot gas). We utilized total infrared plus UV luminosities to estimate star formation rates (SFRs) and K-band luminosities and optical colors to estimate stellar masses (M_{sstarf}) for the sample. Under the assumption that the galaxy-wide 2-10 keV luminosity (L ^gal_HX) traces the combined emission from high-mass X-ray binaries (HMXBs) and low-mass X-ray binaries, and that the power output from these components is linearly correlated with SFR and M_{sstarf}, respectively, we constrain the relation L ^gal_HX= αM_{sstarf}+ βSFR. To achieve this, we construct a Chandra-based data set composed of our new LIRG sample combined with additional samples of less actively star-forming normal galaxies and more powerful LIRGs and ultraluminous infrared galaxies (ULIRGs) from the literature. Using these data, we measure best-fit values of α = (9.05±0.37)x10²⁸ erg/s M^–1_☉ and β = (1.62±0.22)x10³⁹ erg/s (M_☉/yr)^–1. This scaling provides a more physically meaningful estimate of L ^gal_HX, with ~0.1-0.2 dex less scatter, than a direct linear scaling with SFR. Our results suggest that HMXBs dominate the galaxy-wide X-ray emission for galaxies with SFR/M_{sstarf}≳ 5.9x10^–11/yr, a factor of ~2.9 times lower than previous estimates. We find that several of the most powerful LIRGs and ULIRGs, with SFR/M_{sstarf}≳ 10^–9/yr, appear to be X-ray underluminous with respect to our best-fit relation. We argue that these galaxies are likely to contain X-ray binaries residing in compact star-forming regions that are buried under thick galactic columns large enough to attenuate emission in the 2-10 keV band (N_H ≳ 10²³/cm2).