We propose a model of quasar lifetimes in which observational quasar lifetimes and an intrinsic lifetime of rapid accretion are strongly distinguished by the physics of obscuration by surrounding gas and dust .
Quasars are powered by gas funneled to galaxy centers , but for a large part of the accretion lifetime they are heavily obscured by the large gas densities powering accretion .
During this obscured phase , starbursts and black hole growth are fueled but the quasar is buried .
Eventually , feedback from the accretion energy disperses surrounding gas and creates a window in which the black hole is observable optically as a quasar , until the accretion rate drops below that required to maintain a quasar luminosity .
We model this process and measure the unobscured and intrinsic quasar lifetimes in a hydrodynamical simulation of a major galaxy merger .
The bolometric luminosity of the source is determined from the black hole accretion rate , calculated from the local gas properties .
We calculate the column density of hydrogen to the central galactic black hole along multiple lines-of-sight in the simulation , and use these column densities and the gas metallicity to determine the B-band attenuation of the central source .
Defining the observable quasar lifetime as the total time with an observed B-band luminosity greater than some lower limit L _ { B,min } , we find lifetimes \sim 10 - 20 Myr for L _ { B,min } = 10 ^ { 11 } L _ { \sun } ( M _ { B } \approx - 23 ) , in good agreement with observationally determined quasar lifetimes .
These numbers are significantly smaller than the ‘ ‘ intrinsic ’ ’ lifetime \sim 100 Myr obtained if attenuation is neglected .
We find similar lifetimes defined by an observed bolometric luminosity greater than 10 \% of the Eddington luminosity .
The ratio of observed lifetimes to intrinsic lifetime is also strong function of both the limiting luminosity and the observed frequency .