[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 (Lb) is generally inferred from the [OIII] emission line luminosity (LOIII). The key issue in estimating the bolometric luminosity in these AGN, is therefore to know the bolometric correction to be applied to LOIII. A complication arises from the observed LOIII being affected by extinction, most likely from dust within the narrow line region. The extinction-corrected [OIII] luminosity (LOIII c) is a better estimator of the nuclear luminosity than LOIII. However, only the bolometric correction to be applied to the uncorrected LOIII has been evaluated so far. [Aims]: This paper is devoted to estimating the bolometric correction COIII = L b/ LOIII 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 LOIII c and X-ray luminosities (Lx). To estimate COIII, we combined the observed correlation between LOIII c and LX with the X-ray bolometric correction. [Results]: In contrast to previous studies, we found a linear correlation between LOIII c and LX. We estimated COIII using an earlier luminosity-dependent X-ray bolometric correction, and we found a mean value of COIII in the luminosity ranges log LOIII = 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.

This work benefitted from an Italy-Spain Integrated Actions, reference HI-0079. A.L., G.M., and S.B. acknowledge financial support from ASI (grant I/088/06/0). X.B. and F.J.C. acknowledge financial support by the Spanish Ministerio de Ciencia e Innovación under project ESP2006-13608-C02-01.

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