Dr. Hassen Yesuf is coming to visit us on Dec 11th-12th. He will give a talk at 9:30am on Dec 12th (Wednesday).The title and abstract of Dr. Hassen Yesuf's talk is listed below.
Title: The activation of black holes (AGN fraction) and the accretion rates onto them depend both on gas fraction and bulge types.
Abstract：In this talk, I will present my recent work in which we use the bulge-type classifications of representative galaxies from the Sloan Digital Sky Survey by Gadotti (2009) to classify galaxies into real bulges and pseudobulges using a machine learning algorithm. We use structural and stellar population predictors that can be measured easily without resorting to careful image decomposition into bulge, bar and disc as used for the sample we use to train the algorithm. We find that multiple parameters such as the central mass density within 1 kpc, the concentration index, and Sersic index result in a more accurate bulge classification when combined together. We classify several thousands of the SDSS galaxies into real bulges or pseudobulges with 93 ± 2% accuracy. We then show that about 75 − 90% of AGNs are hosted by galaxies with real bulges. The pseudobulge fraction significantly decreases with AGN line ratio signatures as the ratios change from indicating pure star formation (∼ 55 ± 3 %), to composite of star formation and AGN (∼ 20 ± 2%), and to AGN-dominated galaxies (∼ 8 ± 2%). Using the dust-corrected [O III] luminosity as an AGN accretion indicator, we find that AGNs in host galaxies with real bulges have lower [O III] luminosity per black hole mass (Eddington ratios) than AGNs in pseudobulges. Real bulges have a wide range of AGN and star formation activity. The distribution of specific star formation rates (or the WISE 12 μm to 4.6 μm flux ratios) in skewed toward low SSFR for real bulges compared to that of pseudobulges. For both bulge types, the specific black hole accretion rates are significantly correlated with both specific star formation rates and bulge types. Real bulges have lower specific accretion rate but higher AGN fraction than pseudobulges do at similar specific star formation rates. Toward the end of the talk, I will also present a related work on cold gas in AGNs.