The Chandra Deep Field North survey. XIV. X-ray-detected obscured AGNs and starburst galaxies in the bright submillimeter source population

D. M. Alexander, F. E. Bauer, W. N. Brandt, A. E. Hornschemeier, C. Vignali, G. P. Garmire, D. P. Schneider, G. Chartas, S. C. Gallagher

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Abstract

We provide X-ray constraints and perform the first X-ray spectral analyses for bright SCUBA sources (f850 μm ≥ 5 mJy; signal-to-noise ratio ≥4) in an 8′.4 × 8′.4 area of the 2 Ms Chandra Deep Field North survey containing the Hubble Deep Field North. X-ray emission is detected from seven of the 10 bright submillimeter sources in this region down to 0.5-8.0 keV fluxes of ≈1 × 10-16 ergs cm-2 s-1, corresponding to an X-ray-detected submillimeter source density of 360-130+190 deg-2; our analyses suggest that this equates to an X-ray-detected fraction of the bright submillimeter source population of ≲ 36%, although systematic effects may be present. Two of the X-ray-detected sources have nearby (within 3″) X-ray companions, suggesting merging/interacting sources or gravitational lensing effects, and three of the X-ray-detected sources lie within the approximate extent of the protocluster candidate CXOHDFN J123620.0+621554. Five of the X-ray-detected sources have flat effective X-ray spectral slopes (Γ < 1.0), suggesting obscured AGN activity. X-ray spectral analyses suggest that one of these AGNs may be a Compton-thick source; of the other four AGNs, three appear to be Compton-thin sources and one has poor constraints. The rest-frame unabsorbed X-ray luminosities of these AGNs are more consistent with those of Seyfert galaxies than QSOs (i.e., LX ≈ 1043-10 44 ergs s-1). Thus, the low X-ray detection rate of bright submillimeter sources by moderately deep X-ray surveys appears to be due to the relatively low luminosities of the AGNs in these sources rather than Compton-thick absorption. A comparison of these sources with the well-studied, heavily obscured AGN NGC 6240 shows that the average AGN contribution is negligible at submillimeter wavelengths. The X-ray properties of the other two X-ray-detected sources are consistent with those expected from luminous star formation; however, we cannot rule out the possibility that low-luminosity AGNs are present. The three X-ray-undetected sources appear to lie at high redshift (z > 4) and could be either AGNs or starburst galaxies.

Original languageEnglish (US)
Pages (from-to)383-397
Number of pages15
JournalAstronomical Journal
Volume125
Issue number2 1766
DOIs
StatePublished - Jan 1 2003

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Alexander, D. M., Bauer, F. E., Brandt, W. N., Hornschemeier, A. E., Vignali, C., Garmire, G. P., Schneider, D. P., Chartas, G., & Gallagher, S. C. (2003). The Chandra Deep Field North survey. XIV. X-ray-detected obscured AGNs and starburst galaxies in the bright submillimeter source population. Astronomical Journal, 125(2 1766), 383-397. https://doi.org/10.1086/346088