A CHANDRA PERSPECTIVE ON GALAXY-WIDE X-RAY BINARY EMISSION AND ITS CORRELATION WITH STAR FORMATION RATE AND STELLAR MASS: NEW RESULTS FROM LUMINOUS INFRARED GALAXIES
- Johns Hopkins University, Homewood Campus, Baltimore, MD 21218 (United States)
- Department of Physics, University of Durham, South Road, Durham, DH1 3LE (United Kingdom)
- Pontificia Universidad Catolica de Chile, Departamento de Astronomia y Astrofisica, Casilla 306, Santiago 22 (Chile)
- Department of Astronomy and Astrophysics, 525 Davey Lab, Pennsylvania State University, University Park, PA 16802 (United States)
- NASA Goddard Space Flight Centre, Code 662, Greenbelt, MD 20771 (United States)
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{sub H} {approx}< 5 x 10{sup 20} cm{sup -2}. The LIRGs in our sample have total infrared (8-1000 {mu}m) luminosities in the range of L{sub IR{approx}} (1-8) x 10{sup 11} L{sub sun}. 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{sub *}) for the sample. Under the assumption that the galaxy-wide 2-10 keV luminosity (L {sup gal}{sub 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{sub *}, respectively, we constrain the relation L {sup gal}{sub HX} = {alpha}M{sub *} + {beta}SFR. 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 {alpha} = (9.05 {+-} 0.37) x 10{sup 28} erg s{sup -1} M {sup -1}{sub sun} and {beta} = (1.62 {+-} 0.22) x 10{sup 39} erg s{sup -1} (M{sub sun} yr{sup -1}){sup -1}. This scaling provides a more physically meaningful estimate of L {sup gal}{sub HX}, with {approx}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{sub *} {approx}>5.9 x 10{sup -11} yr{sup -1}, a factor of {approx}2.9 times lower than previous estimates. We find that several of the most powerful LIRGs and ULIRGs, with SFR/M{sub *} {approx}> 10{sup -9} yr{sup -1}, 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{sub H} {approx}> 10{sup 23} cm{sup -2}).
- OSTI ID:
- 21471178
- Journal Information:
- Astrophysical Journal, Vol. 724, Issue 1; Other Information: DOI: 10.1088/0004-637X/724/1/559; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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