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Centro de Astrofísica da Universidade do Porto

Present-Day Growth of Black Holes and Bulges: The Sloan Digital Sky Survey Perspective

T. Heckman, G. Kauffmann, J. Brinchmann, S. Charlot, C. Tremonti, S. D. M. White

We investigate the accretion-driven growth of supermassive black holes in the low-redshift universe using 23,000 narrow-emission-line (``type 2'') active galactic nuclei (AGNs) and the complete sample of 123,000 galaxies in the Sloan Digital Sky Survey from which they were drawn. We use the stellar velocity dispersions of the early-type galaxies and AGN hosts to estimate their black hole masses, and we use the AGN [O III] λ5007 emission line luminosities to estimate black hole accretion rates. We find that most present-day accretion occurs onto black holes with masses less than 108 Msolar that reside in moderately massive galaxies (M*~1010-1011.5 Msolar) with high stellar surface mass densities (μ*~108.5-109.5 Msolar kpc-2) and young stellar populations. The volume-averaged accretion rates of low-mass black holes (〈3×107 Msolar) imply that this population is growing on a timescale that is comparable to the age of the universe. Around half this growth takes place in AGNs that are radiating within a factor of 5 of the Eddington luminosity. Such systems are rare, making up only 0.2% of the low-mass black hole population at the present day. The rest of the growth occurs in lower luminosity AGNs. The growth timescale is more than 2 orders of magnitude longer for the population of the most massive black holes in our sample. The volume-averaged ratio of star formation to black hole accretion in bulge-dominated galaxies is ~1000, in remarkable agreement with the observed ratio of stellar mass to black hole mass in nearby galaxy bulges. We conclude that (1) bulge formation and black hole formation are tightly coupled, even in present-day galaxies, and (2) the evolution of the AGN luminosity function documented in recent optical and X-ray surveys is driven by a decrease in the characteristic mass scale of actively accreting black holes.

The Astrophysical Journal
Volume 613, Page 109
September 2004

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Institute of Astrophysics and Space Sciences (IA) is a new but long anticipated research infrastructure with a national dimension. It embodies a bold but feasible vision for the development of Astronomy, Astrophysics and Space Sciences in Portugal, taking full advantage and fully realizing the potential created by the national membership of the European Space Agency (ESA) and the European Southern Observatory (ESO). IA resulted from the merging the two most prominent research units in the field in Portugal: the Centre for Astrophysics of the University of Porto (CAUP) and the Center for Astronomy and Astrophysics of the University of Lisbon (CAAUL). It currently hosts more than two-thirds of all active researchers working in Space Sciences in Portugal, and is responsible for an even greater fraction of the national productivity in international ISI journals in the area of Space Sciences. This is the scientific area with the highest relative impact factor (1.65 times above the international average) and the field with the highest average number of citations per article for Portugal.

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