The relationship between luminosity and broad-line region size in active galactic nuclei

Shai Kaspi, Dan Maoz, Hagai Netzer, Bradley M. Peterson, Marianne Vestergaard, Buell Tomasson Jannuzi

Research output: Contribution to journalArticle

526 Citations (Scopus)

Abstract

We reinvestigate the relationship between the characteristic broad-line region size (RBLR) and the Balmer emission-line, X-ray, UV, and optical continuum luminosities. Our study makes use of the best available determinations of RBLR for a large number of active galactic nuclei (AGNs) from Peterson et al. Using their determinations of RBLR for a large sample of AGNs and two different regression methods, we investigate the robustness of our correlation results as a function of data subsample and regression technique. Although small systematic differences were found depending on the method of analysis, our results are generally consistent. Assuming a power-law relation RBLR ∝ Lα, we find that the mean best-fitting α is about 0.67 ± 0.05 for the optical continuum and the broad Hβ luminosity, about 0.56 ± 0.05 for the UV continuum luminosity, and about 0.70 ± 0.14 for the X-ray luminosity. We also find an intrinsic scatter of ∼40% in these relations. The disagreement of our results with the theoretical expected slope of 0.5 indicates that the simple assumption of all AGNs having on average the same ionization parameter, BLR density, column density, and ionizing spectral energy distribution is not valid and there is likely some evolution of a few of these characteristics along the luminosity scale.

Original languageEnglish (US)
Pages (from-to)61-71
Number of pages11
JournalAstrophysical Journal
Volume629
Issue number1 I
DOIs
StatePublished - Aug 10 2005
Externally publishedYes

Fingerprint

active galactic nuclei
luminosity
continuums
regression analysis
spectral energy distribution
power law
ionization
x rays
slopes
energy
method

Keywords

  • Galaxies: active
  • Galaxies: nuclei
  • Galaxies: Seyfert
  • Quasars: general

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

The relationship between luminosity and broad-line region size in active galactic nuclei. / Kaspi, Shai; Maoz, Dan; Netzer, Hagai; Peterson, Bradley M.; Vestergaard, Marianne; Jannuzi, Buell Tomasson.

In: Astrophysical Journal, Vol. 629, No. 1 I, 10.08.2005, p. 61-71.

Research output: Contribution to journalArticle

Kaspi, Shai ; Maoz, Dan ; Netzer, Hagai ; Peterson, Bradley M. ; Vestergaard, Marianne ; Jannuzi, Buell Tomasson. / The relationship between luminosity and broad-line region size in active galactic nuclei. In: Astrophysical Journal. 2005 ; Vol. 629, No. 1 I. pp. 61-71.
@article{ba7c52ec5017477781be4b5c16331c34,
title = "The relationship between luminosity and broad-line region size in active galactic nuclei",
abstract = "We reinvestigate the relationship between the characteristic broad-line region size (RBLR) and the Balmer emission-line, X-ray, UV, and optical continuum luminosities. Our study makes use of the best available determinations of RBLR for a large number of active galactic nuclei (AGNs) from Peterson et al. Using their determinations of RBLR for a large sample of AGNs and two different regression methods, we investigate the robustness of our correlation results as a function of data subsample and regression technique. Although small systematic differences were found depending on the method of analysis, our results are generally consistent. Assuming a power-law relation RBLR ∝ Lα, we find that the mean best-fitting α is about 0.67 ± 0.05 for the optical continuum and the broad Hβ luminosity, about 0.56 ± 0.05 for the UV continuum luminosity, and about 0.70 ± 0.14 for the X-ray luminosity. We also find an intrinsic scatter of ∼40{\%} in these relations. The disagreement of our results with the theoretical expected slope of 0.5 indicates that the simple assumption of all AGNs having on average the same ionization parameter, BLR density, column density, and ionizing spectral energy distribution is not valid and there is likely some evolution of a few of these characteristics along the luminosity scale.",
keywords = "Galaxies: active, Galaxies: nuclei, Galaxies: Seyfert, Quasars: general",
author = "Shai Kaspi and Dan Maoz and Hagai Netzer and Peterson, {Bradley M.} and Marianne Vestergaard and Jannuzi, {Buell Tomasson}",
year = "2005",
month = "8",
day = "10",
doi = "10.1086/431275",
language = "English (US)",
volume = "629",
pages = "61--71",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "1 I",

}

TY - JOUR

T1 - The relationship between luminosity and broad-line region size in active galactic nuclei

AU - Kaspi, Shai

AU - Maoz, Dan

AU - Netzer, Hagai

AU - Peterson, Bradley M.

AU - Vestergaard, Marianne

AU - Jannuzi, Buell Tomasson

PY - 2005/8/10

Y1 - 2005/8/10

N2 - We reinvestigate the relationship between the characteristic broad-line region size (RBLR) and the Balmer emission-line, X-ray, UV, and optical continuum luminosities. Our study makes use of the best available determinations of RBLR for a large number of active galactic nuclei (AGNs) from Peterson et al. Using their determinations of RBLR for a large sample of AGNs and two different regression methods, we investigate the robustness of our correlation results as a function of data subsample and regression technique. Although small systematic differences were found depending on the method of analysis, our results are generally consistent. Assuming a power-law relation RBLR ∝ Lα, we find that the mean best-fitting α is about 0.67 ± 0.05 for the optical continuum and the broad Hβ luminosity, about 0.56 ± 0.05 for the UV continuum luminosity, and about 0.70 ± 0.14 for the X-ray luminosity. We also find an intrinsic scatter of ∼40% in these relations. The disagreement of our results with the theoretical expected slope of 0.5 indicates that the simple assumption of all AGNs having on average the same ionization parameter, BLR density, column density, and ionizing spectral energy distribution is not valid and there is likely some evolution of a few of these characteristics along the luminosity scale.

AB - We reinvestigate the relationship between the characteristic broad-line region size (RBLR) and the Balmer emission-line, X-ray, UV, and optical continuum luminosities. Our study makes use of the best available determinations of RBLR for a large number of active galactic nuclei (AGNs) from Peterson et al. Using their determinations of RBLR for a large sample of AGNs and two different regression methods, we investigate the robustness of our correlation results as a function of data subsample and regression technique. Although small systematic differences were found depending on the method of analysis, our results are generally consistent. Assuming a power-law relation RBLR ∝ Lα, we find that the mean best-fitting α is about 0.67 ± 0.05 for the optical continuum and the broad Hβ luminosity, about 0.56 ± 0.05 for the UV continuum luminosity, and about 0.70 ± 0.14 for the X-ray luminosity. We also find an intrinsic scatter of ∼40% in these relations. The disagreement of our results with the theoretical expected slope of 0.5 indicates that the simple assumption of all AGNs having on average the same ionization parameter, BLR density, column density, and ionizing spectral energy distribution is not valid and there is likely some evolution of a few of these characteristics along the luminosity scale.

KW - Galaxies: active

KW - Galaxies: nuclei

KW - Galaxies: Seyfert

KW - Quasars: general

UR - http://www.scopus.com/inward/record.url?scp=26844463737&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=26844463737&partnerID=8YFLogxK

U2 - 10.1086/431275

DO - 10.1086/431275

M3 - Article

AN - SCOPUS:26844463737

VL - 629

SP - 61

EP - 71

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 1 I

ER -