Accretion and star formation rates in low-redshift type II active galactic nuclei

Accretion and star formation (SF) rates in low-redshift Sloan Digital Sky Survey type II active galactic nuclei (AGN) are critically evaluated. Comparison with photoionization models indicates that bolometric luminosity (L _bol) estimates based on L([O iii] λ5007) severely underestimate L_bol in low-ionization sources such as LINERs. An alternative method based on L(Hβ) is less sensitive to the ionization level, and a novel method, based on a combination of L([O iii] λ5007) and L([O i] λ6300), is perhaps the best. Using this method, I show that low-ionization AGN are accreting faster than assumed until now. Other significant related findings are as follows. (1) Any type II AGN property related to the black hole (BH) mass is more reliably obtained by removing blue galaxies from the sample. (2) Seyfert 2s and LINER 2s form a continuous sequence of L/L_Edd with no indication for a change in accretion mechanism or mode of mass supply. There are very few, if any, LINERs in all type I samples which results in a much narrower L/L_Edd distribution compared with type II samples. (3) There is a strong correlation between the SF luminosity, L_SF, and L_bol over more than five orders of magnitude in luminosity. This leads to a simple relationship between bulge and BH growth rates, g(bulge)/g(BH) ∝ L^-0.2_bol, where g(bulge)/g(BH) ≃ 115 for L_bol = 10⁴² erg s ^-1. Seyfert 2s and LINER 2s follow the same L_SF-L _bol correlation for all sources with a stellar age indicator, D _n4000, smaller than 1.8. This suggests that a similar fraction of SF gas finds its way to the centre in all AGN. (4) L_bol, L_SF, L/L_Edd and the specific SF rate follow D_n4000 in a similar way.