The X-ray-to-optical properties of optically selected active galaxies over wide luminosity and redshift ranges

A. T. Steffen, I. Strateva, William Nielsen Brandt, D. M. Alexander, A. M. Koekemoer, B. D. Lehmer, Donald P. Schneider, C. Vignali

Research output: Contribution to journalArticle

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Abstract

We present partial-correlation analyses that examine the strengths of the relationships between l 2500 Å l 2kev, α ox, and redshift for optically selected active galactic nuclei (AGNs). We extend the work of Strateva and coworkers, which analyzed optically selected AGNs from the Sloan Digital Sky Survey (SDSS), by including 52 moderateluminosity, optically selected AGNs from the COMBO-17 survey with corresponding deep (≈250 ks to 1 Ms) X-ray observations from the Extended Chandra Deep Field-South. The COMBO-17 survey extend ∼3 mag deeper than the SDSS and probes the moderate-luminosity AGNs that numerically dominate the AGN population in the universe. We also include recently published observations of 19 high-redshift, optically selected AGNs and 46 luminous, low-redshift AGNs from the Bright Quasar Survey. The full sample used in our analysis consists of 333 AGNs, extending out to z ∼ 6, with 293 (88%) having X-ray detections. The sample spans five decades in UV luminosity and four decades in X-ray luminosity. We confirm that αOX is strongly anticorrelated with l 2500 Å (13.6 σ), the highest significance found for this relation to date, and find evidence suggesting that the slope of this relation may be dependent on l 2500 Å. We find that no significant correlation exists between a ox and redshift (1.3 σ) and constrain the maximum evolution of AGN UV-to-X-ray flux ratios to be less than 30% (1 σ) out to z = 5. Using our sample's high X-ray detection fraction, we also find a significant anticorrelation (3.0 σ) between α ox and l 2kev. We make comparisons to earlier studies on this topic and discuss implications for X-ray and optical AGN luminosity functions.

Original languageEnglish (US)
Pages (from-to)2826-2842
Number of pages17
JournalAstronomical Journal
Volume131
Issue number6
DOIs
StatePublished - Jun 1 2006

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active galaxies
active galactic nuclei
optical property
luminosity
optical properties
x rays
probe
quasars
universe
slopes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Steffen, A. T., Strateva, I., Brandt, W. N., Alexander, D. M., Koekemoer, A. M., Lehmer, B. D., ... Vignali, C. (2006). The X-ray-to-optical properties of optically selected active galaxies over wide luminosity and redshift ranges. Astronomical Journal, 131(6), 2826-2842. https://doi.org/10.1086/503627
Steffen, A. T. ; Strateva, I. ; Brandt, William Nielsen ; Alexander, D. M. ; Koekemoer, A. M. ; Lehmer, B. D. ; Schneider, Donald P. ; Vignali, C. / The X-ray-to-optical properties of optically selected active galaxies over wide luminosity and redshift ranges. In: Astronomical Journal. 2006 ; Vol. 131, No. 6. pp. 2826-2842.
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abstract = "We present partial-correlation analyses that examine the strengths of the relationships between l 2500 {\AA} l 2kev, α ox, and redshift for optically selected active galactic nuclei (AGNs). We extend the work of Strateva and coworkers, which analyzed optically selected AGNs from the Sloan Digital Sky Survey (SDSS), by including 52 moderateluminosity, optically selected AGNs from the COMBO-17 survey with corresponding deep (≈250 ks to 1 Ms) X-ray observations from the Extended Chandra Deep Field-South. The COMBO-17 survey extend ∼3 mag deeper than the SDSS and probes the moderate-luminosity AGNs that numerically dominate the AGN population in the universe. We also include recently published observations of 19 high-redshift, optically selected AGNs and 46 luminous, low-redshift AGNs from the Bright Quasar Survey. The full sample used in our analysis consists of 333 AGNs, extending out to z ∼ 6, with 293 (88{\%}) having X-ray detections. The sample spans five decades in UV luminosity and four decades in X-ray luminosity. We confirm that αOX is strongly anticorrelated with l 2500 {\AA} (13.6 σ), the highest significance found for this relation to date, and find evidence suggesting that the slope of this relation may be dependent on l 2500 {\AA}. We find that no significant correlation exists between a ox and redshift (1.3 σ) and constrain the maximum evolution of AGN UV-to-X-ray flux ratios to be less than 30{\%} (1 σ) out to z = 5. Using our sample's high X-ray detection fraction, we also find a significant anticorrelation (3.0 σ) between α ox and l 2kev. We make comparisons to earlier studies on this topic and discuss implications for X-ray and optical AGN luminosity functions.",
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The X-ray-to-optical properties of optically selected active galaxies over wide luminosity and redshift ranges. / Steffen, A. T.; Strateva, I.; Brandt, William Nielsen; Alexander, D. M.; Koekemoer, A. M.; Lehmer, B. D.; Schneider, Donald P.; Vignali, C.

In: Astronomical Journal, Vol. 131, No. 6, 01.06.2006, p. 2826-2842.

Research output: Contribution to journalArticle

TY - JOUR

T1 - The X-ray-to-optical properties of optically selected active galaxies over wide luminosity and redshift ranges

AU - Steffen, A. T.

AU - Strateva, I.

AU - Brandt, William Nielsen

AU - Alexander, D. M.

AU - Koekemoer, A. M.

AU - Lehmer, B. D.

AU - Schneider, Donald P.

AU - Vignali, C.

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N2 - We present partial-correlation analyses that examine the strengths of the relationships between l 2500 Å l 2kev, α ox, and redshift for optically selected active galactic nuclei (AGNs). We extend the work of Strateva and coworkers, which analyzed optically selected AGNs from the Sloan Digital Sky Survey (SDSS), by including 52 moderateluminosity, optically selected AGNs from the COMBO-17 survey with corresponding deep (≈250 ks to 1 Ms) X-ray observations from the Extended Chandra Deep Field-South. The COMBO-17 survey extend ∼3 mag deeper than the SDSS and probes the moderate-luminosity AGNs that numerically dominate the AGN population in the universe. We also include recently published observations of 19 high-redshift, optically selected AGNs and 46 luminous, low-redshift AGNs from the Bright Quasar Survey. The full sample used in our analysis consists of 333 AGNs, extending out to z ∼ 6, with 293 (88%) having X-ray detections. The sample spans five decades in UV luminosity and four decades in X-ray luminosity. We confirm that αOX is strongly anticorrelated with l 2500 Å (13.6 σ), the highest significance found for this relation to date, and find evidence suggesting that the slope of this relation may be dependent on l 2500 Å. We find that no significant correlation exists between a ox and redshift (1.3 σ) and constrain the maximum evolution of AGN UV-to-X-ray flux ratios to be less than 30% (1 σ) out to z = 5. Using our sample's high X-ray detection fraction, we also find a significant anticorrelation (3.0 σ) between α ox and l 2kev. We make comparisons to earlier studies on this topic and discuss implications for X-ray and optical AGN luminosity functions.

AB - We present partial-correlation analyses that examine the strengths of the relationships between l 2500 Å l 2kev, α ox, and redshift for optically selected active galactic nuclei (AGNs). We extend the work of Strateva and coworkers, which analyzed optically selected AGNs from the Sloan Digital Sky Survey (SDSS), by including 52 moderateluminosity, optically selected AGNs from the COMBO-17 survey with corresponding deep (≈250 ks to 1 Ms) X-ray observations from the Extended Chandra Deep Field-South. The COMBO-17 survey extend ∼3 mag deeper than the SDSS and probes the moderate-luminosity AGNs that numerically dominate the AGN population in the universe. We also include recently published observations of 19 high-redshift, optically selected AGNs and 46 luminous, low-redshift AGNs from the Bright Quasar Survey. The full sample used in our analysis consists of 333 AGNs, extending out to z ∼ 6, with 293 (88%) having X-ray detections. The sample spans five decades in UV luminosity and four decades in X-ray luminosity. We confirm that αOX is strongly anticorrelated with l 2500 Å (13.6 σ), the highest significance found for this relation to date, and find evidence suggesting that the slope of this relation may be dependent on l 2500 Å. We find that no significant correlation exists between a ox and redshift (1.3 σ) and constrain the maximum evolution of AGN UV-to-X-ray flux ratios to be less than 30% (1 σ) out to z = 5. Using our sample's high X-ray detection fraction, we also find a significant anticorrelation (3.0 σ) between α ox and l 2kev. We make comparisons to earlier studies on this topic and discuss implications for X-ray and optical AGN luminosity functions.

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