Universal bolometric corrections for active galactic nuclei over seven luminosity decades

Abstract

Context. The AGN bolometric correction is a key element for understanding black hole (BH) demographics and computing accurate BH accretion histories from AGN luminosities. However, current estimates still differ from each other by up to a factor of two to three, and rely on extrapolations at the lowest and highest luminosities. Aims. Here we revisit this fundamental question by presenting general hard X-ray (KX) and optical (KO) bolometric corrections, computed by combining several AGN samples spanning the widest (about 7 dex) luminosity range ever used for this type of studies. Methods. We analysed a total of ∼1000 type 1 and type 2 AGN for which we performed a dedicated SED-fitting. Results. We provide a bolometric correction separately for type 1 and type 2 AGN; the two bolometric corrections agree in the overlapping luminosity range. Based on this we computed for the first time a universal bolometric correction for the whole AGN sample (both type 1 and type 2). We found that KX is fairly constant at log(LBOL/L⊙) < 11, while it increases up to about one order of magnitude at log(LBOL/L⊙) ∼ 14.5. A similar increasing trend has been observed when its dependence on either the Eddington ratio or the BH mass is considered, while no dependence on redshift up to z ∼ 3.5 has been found. In contrast, the optical bolometric correction appears to be fairly constant (i.e. KO ∼ 5) regardless of the independent variable. We also verified that our bolometric corrections correctly predict the AGN bolometric luminosity functions. According to this analysis, our bolometric corrections can be applied to the whole AGN population in a wide range of luminosity and redshift.