A NuSTAR survey of nearby ultraluminous infrared galaxies

Stacy H. Teng, Jane R. Rigby, Daniel Stern, Andrew Ptak, D. M. Alexander, Franz E. Bauer, Stephen E. Boggs, W. Niel Brandt, Finn Erland Christensen, Andrea Comastri, William W. Craig, Duncan Farrah, Poshak Gandhi, Charles J. Hailey, Fiona A. Harrison, Ryan C. Hickox, Michael Koss, Bin Luo, Ezequiel Treister, William W. Zhang

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We present a Nuclear Spectroscopic Telescope Array (NuSTAR), Chandra, and XMM-Newton survey of nine of the nearest ultraluminous infrared galaxies (ULIRGs). The unprecedented sensitivity of NuSTAR at energies above 10 keV enables spectral modeling with far better precision than was previously possible. Six of the nine sources observed were detected sufficiently well by NuSTAR to model in detail their broadband X-ray spectra, and recover the levels of obscuration and intrinsic X-ray luminosities. Only one source (IRAS 13120-5453) has a spectrum consistent with a Compton-thick active galactic nucleus (AGN), but we cannot rule out that a second source (Arp 220) harbors an extremely highly obscured AGN as well. Variability in column density (reduction by a factor of a few compared to older observations) is seen in IRAS 05189-2524 and Mrk 273, altering the classification of these borderline sources from Compton-thick to Compton-thin. The ULIRGs in our sample have surprisingly low observed fluxes in high-energy (>10 keV) X-rays, especially compared to their bolometric luminosities. They have lower ratios of unabsorbed 2-10 keV to bolometric luminosity, and unabsorbed 2-10 keV to mid-IR [O IV] line luminosity than do Seyfert 1 galaxies. We identify IRAS 08572+3915 as another candidate intrinsically X-ray weak source, similar to Mrk 231. We speculate that the X-ray weakness of IRAS 08572+3915 is related to its powerful outflow observed at other wavelengths.
Original languageEnglish
Article number56
JournalAstrophysical Journal
Issue number1
Number of pages17
Publication statusPublished - 2015


  • Galaxies: active
  • X-rays: galaxies
  • galaxies: individual (IRAS 05189–2524, IRAS 08572+3915, IRAS 10565+2448, Mrk 231, IRAS 13120–5453, Mrk 273, IRAS 14378–3651, Arp 220, the Superantennae)


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