A unified model for the evolution of galaxies and quasars

A unified model for the evolution of galaxies and quasars

Accepted 1999 September 2. Received 1999 August 20; in original form 1999 July 5 | Guinevere Kauffmann* and Martin Haehnelt
The paper presents a unified model that incorporates the growth of supermassive black holes into semi-analytic models of galaxy formation and evolution in a cold dark matter-dominated universe. The model assumes that supermassive black holes form and are fueled during major mergers of galaxies. When two galaxies merge, their central black holes coalesce, and a few percent of the gas in the merger remnant is accreted by the new black hole over a timescale of a few million years. This model successfully reproduces various observed phenomena, including the relation between bulge luminosity and black hole mass in nearby galaxies, the evolution of the quasar population with redshift, and the relationship between quasar luminosities and those of their host galaxies. The decline in the number density of quasars from \( z \approx 2 \) to \( z = 0 \) is attributed to three factors: a decrease in the merging rate, a reduction in the amount of cold gas available to fuel black holes, and an increase in the time-scale for gas accretion. The predicted decline in the total content of cold gas in galaxies aligns with observations of damped Lyα systems. The results suggest that the evolution of supermassive black holes, quasars, and starburst galaxies is closely linked to the hierarchical build-up of galaxies.The paper presents a unified model that incorporates the growth of supermassive black holes into semi-analytic models of galaxy formation and evolution in a cold dark matter-dominated universe. The model assumes that supermassive black holes form and are fueled during major mergers of galaxies. When two galaxies merge, their central black holes coalesce, and a few percent of the gas in the merger remnant is accreted by the new black hole over a timescale of a few million years. This model successfully reproduces various observed phenomena, including the relation between bulge luminosity and black hole mass in nearby galaxies, the evolution of the quasar population with redshift, and the relationship between quasar luminosities and those of their host galaxies. The decline in the number density of quasars from \( z \approx 2 \) to \( z = 0 \) is attributed to three factors: a decrease in the merging rate, a reduction in the amount of cold gas available to fuel black holes, and an increase in the time-scale for gas accretion. The predicted decline in the total content of cold gas in galaxies aligns with observations of damped Lyα systems. The results suggest that the evolution of supermassive black holes, quasars, and starburst galaxies is closely linked to the hierarchical build-up of galaxies.
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[slides and audio] A unified model for the evolution of galaxies and quasars