The bolometric luminosity of type 2 AGN from extinction-corrected [OIII]: no evidence of Eddington-limited sources

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 (L-OIII(c)) 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 C-OIII = L-b/L-OIII(c) 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 L-OIII(c) and X-ray luminosities (L-X). To estimate C-OIII, we combined the observed correlation between L-OIII(c) and L-Xwith the X-ray bolometric correction. Results. In contrast to previous studies, we found a linear correlation between L-OIII(c) 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 0.3 < z < 0.4 and found that these sources are not accreting near their Eddington limit, contrary to previous claims.