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

Lehmer, B.D.; Alexander, D.M.; Bauer, F.E.; Brandt, W.N.; Goulding, A.D.; Jenkins, L.P.; Ptak, A.; Roberts, T.P.

Abstract

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 <~ 5 × 1020 cm-2. The LIRGs in our sample have total infrared (8-1000 μm) luminosities in the range of L IR≈ (1-8) × 1011 L 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 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) × 1028 erg s-1 M -1 sun and β = (1.62 ± 0.22) × 1039 erg s-1 (M sun yr-1)-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 gsim5.9 × 10-11 yr-1, 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-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 H >~ 1023 cm-2).

Citation

Lehmer, B., Alexander, D., Bauer, F., Brandt, W., Goulding, A., Jenkins, L., …Roberts, T. (2010). 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. Astrophysical Journal, 724(1), 559-571. https://doi.org/10.1088/0004-637x/724/1/559

• Journal Article Type: Article
• Publication Date: Nov 1, 2010
• Deposit Date: Jan 30, 2012
• Publicly Available Date: Jan 3, 2014
• Journal: Astrophysical Journal
• Print ISSN: 0004-637X
• Electronic ISSN: 1538-4357
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 724
• Issue: 1
• Pages: 559-571
• DOI: https://doi.org/10.1088/0004-637x/724/1/559
• Keywords: Cosmology, Observations, Galaxies, Starburst, Infrared, X-rays, Binaries.
• Public URL: https://durham-repository.worktribe.com/output/1488813