The bolometric luminosity of type 2 AGN from extinction-corrected [OIII]

No evidence of Eddington-limited sources

¹ Dipartimento di Fisica “E. Amaldi”, Università degli Studi Roma Tre, via della Vasca Navale 84, 00146 Roma, Italy e-mail: lamastra@fis.uniroma3.it
² Instituto de Física de Cantabria (CSIC-UC), Avenida de los Castros, 39005 Santander, Spain

Received: 10 March 2009
Accepted: 27 May 2009

Abstract

Context. There have been recent claims that a significant fraction of type 2 AGN accrete close to or even above the Eddington limit. In type 2 AGN, the bolometric luminosity (L_b) is generally inferred from the [OIII] emission line luminosity (L_OIII). The key issue in estimating the bolometric luminosity in these AGN, is therefore to know the bolometric correction to be applied to L_OIII. A complication arises from the observed L_OIII being affected by extinction, most likely from dust within the narrow line region. The extinction-corrected [OIII] luminosity () is a better estimator of the nuclear luminosity than L_OIII. However, only the bolometric correction to be applied to the uncorrected L_OIII has been evaluated so far.

Aims. This paper is devoted to estimating the bolometric correction / for deriving the Eddington ratios for the type 2 AGN in a sample of SDSS objects.

Methods. We collected 61 sources from the literature with reliable estimates of both and X-ray luminosities (L_X). To estimate C_OIII, we combined the observed correlation between and L_X with the X-ray bolometric correction.

Results. In contrast to previous studies, we found a linear correlation between and L_X. We estimated C_OIII using an earlier luminosity-dependent X-ray bolometric correction, and we found a mean value of C_OIII in the luminosity ranges log L_OIII = 38–40, 40–42, and 42–44 of 87, 142, and 454, respectively. We used it to calculate the Eddington ratio distribution of type 2 SDSS AGN at and found that these sources are not accreting near their Eddington limit, contrary to previous claims.