The chandra multi-wavelength project: Optical spectroscopy and the broadband spectral energy distributions of X-ray-selected AGNs

Markos Trichas, Paul J. Green, John D. Silverman, Tom Aldcroft, Wayne Barkhouse, Robert A. Cameron, Anca Constantin, Sara L. Ellison, Craig Foltz, Daryl Haggard, Buell T. Jannuzi, Dong Woo Kim, Herman L. Marshall, Amy Mossman, Laura M. Pérez, Encarni Romero-Colmenero, Angel Ruiz, Malcolm G. Smith, Paul S. Smith, Guillermo TorresDaniel R. Wik, Belinda J. Wilkes, Angie Wolfgang

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38 Scopus citations


From optical spectroscopy of X-ray sources observed as part of the Chandra Multi-wavelength Project (ChaMP), we present redshifts and classifications for a total of 1569 Chandra sources from our targeted spectroscopic follow-up using the FLWO/1.5m, SAAO/1.9m, WIYN 3.5m, CTIO/4m, KPNO/4m, Magellan/6.5m, MMT/6.5m, and Gemini/8m telescopes, and from archival Sloan Digital Sky Survey (SDSS) spectroscopy. We classify the optical counterparts as 50% broad-line active galactic nuclei (AGNs), 16% emission line galaxies, 14% absorption line galaxies, and 20% stars. We detect QSOs out to z ∼ 5.5 and galaxies out to z ∼ 3. We have compiled extensive photometry, including X-ray (ChaMP), ultraviolet (GALEX), optical (SDSS and ChaMP-NOAO/MOSAIC follow-up), near-infrared (UKIDSS, Two Micron All Sky Survey, and ChaMP-CTIO/ISPI follow-up), mid-infrared (WISE), and radio (FIRST and NVSS) bands. Together with our spectroscopic information, this enables us to derive detailed spectral energy distributions (SEDs) for our extragalactic sources. We fit a variety of template SEDs to determine bolometric luminosities, and to constrain AGNs and starburst components where both are present. While 58% of X-ray Seyferts (1042 erg s-1 < L 2 - 10 keV <10 44ergs-1) require a starburst event (>5% starburst contribution to bolometric luminosity) to fit observed photometry only 26% of the X-ray QSO (L 2 - 10 keV >1044ergs-1) population appear to have some kind of star formation contribution. This is significantly lower than for the Seyferts, especially if we take into account torus contamination at z > 1 where the majority of our X-ray QSOs lie. In addition, we observe a rapid drop of the percentage of starburst contribution as X-ray luminosity increases. This is consistent with the quenching of star formation by powerful QSOs, as predicted by the merger model, or with a time lag between the peak of star formation and QSO activity. We have tested the hypothesis that there should be a strong connection between X-ray obscuration and star formation but we do not find any association between X-ray column density and star formation rate both in the general population or the star-forming X-ray Seyferts. Our large compilation also allows us to report here the identification of 81 X-ray Bright Optically inactive Galaxies, 78 z > 3 X-ray sources, and eight Type-2 QSO candidates. Also, we have identified the highest redshift (z = 5.4135) X-ray-selected QSO with optical spectroscopy.

Original languageEnglish (US)
Article number17
JournalAstrophysical Journal, Supplement Series
Issue number2
StatePublished - Jun 2012

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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