Astronomy and Astrophysics – Astrophysics – Galaxy Astrophysics
Scientific paper
2009-07-21
Astronomy and Astrophysics
Astrophysics
Galaxy Astrophysics
16 pages, 16 figures, accepted for publication in MNRAS
Scientific paper
Accretion and star formation (SF) rates in low redshift SDSS type-II active galactic nuclei (AGN) are critically evaluated. Comparison with photoionization models indicates that bolometric luminosity (Lbol) estimates based on L(oiii 5007A) severely underestimate Lbol in low ionization sources such as LINERs. An alternative method based on L(hb) is less sensitive to ionization level and a novel method, based on a combination of L(oiii 5007A) and L(oi 6300A), is erhaps the best. Using this method I show that low ionization AGN are accreting faster than assumed until now. Significant related other findings are: 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/Ledd 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 arrower L/Ledd distribution compared with type-II samples. 3. There is a strong correlation between SF luminosity, Lsf, and Lbol 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) propto Lbol^(-0.2), where g(bulge)/g(BH) = 115 for Lbol=10^42 erg/sec. Seyfert 2s and LINER 2s follow the same Lsf-Lbol correlation for all sources with a stellar age indicator, D4000, smaller than 1.8. This suggests that a similar fraction of SF gas finds its way to the center in all AGN. 4. Lbol, Lsf, L/Ledd and the specific SF rate follow D4000 in a similar way.
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