Fuelling quasars with hot gas
نویسندگان
چکیده
We consider a model for quasar formation in which massive black holes are formed and fuelled largely by the accretion of hot gas during the process of galaxy formation. In standard hierarchical collapse models, objects about the size of normal galaxies and larger form a dense hot atmosphere when they collapse. We show that if such an atmosphere forms a nearly ‘maximal’ cooling flow, then a central black hole can accrete at close to its Eddington limit. This leads to exponential growth of a seed black hole, resulting in a quasar in some cases. In this model, the first quasars form soon after the first collapses to produce hot gas. The hot gas is depleted as time progresses, mostly by cooling, so that the accretion rate eventually falls below the threshold for advection-dominated accretion, at which stage radiative efficiency plummets and any quasar turns off. A simple implementation of this model, incorporated into a semi-analytical model for galaxy formation, overproduces quasars when compared with observed luminosity functions, but is consistent with models of the X-ray background, which indicate that most accretion is obscured. It produces few quasars at high redshift owing to the lack of time needed to grow massive black holes. Quasar fuelling by hot gas provides a minimum level, sufficient to power most quasars at redshifts between one and two, to which other sources of fuel can be added. The results are sensitive to feedback effects, such as might result from radio jets and other outflows.
منابع مشابه
Location Ordination for LNG Fuelling Station in the Persian Gulf Ports of Iran Using Analytic Hierarchy Process (AHP)
Usage of the new and alternative clean fuel is becoming a hot topic in marine transportation in accordance with environmental regulations of I.M.O. Using L.N.G as the ship fuel is a reliable and long term solution for environmental issues. Iran owing to its large number of natural gas fields and unique geographical position, has adequate potential to provide services to shipping fleets. Finding...
متن کاملThe impact of dust in host galaxies on quasar luminosity functions
We have investigated effects of dust attenuation on quasar luminosity functions at z ∼ 2 using a semi-analytic galaxy formation model combined with a large cosmological N-body simulation. We estimate the dust attenuation of quasars self-consistently with that of galaxies by considering the dust in their host bulges. We find that the luminosity of the bright quasars is strongly dimmed by the dus...
متن کاملDual-Fuelling of a Direct-Injection Automotive Diesel Engine by Diesel-Gas Method
Use of liquefied petroleum gas (LPG) in compression-ignition (C-I) engines has always been considered important in the diesel engineering field. This is due to its easy accessibility and good combustion characteristics. In this paper the application of LPG fuel along with diesel oil in a direct- injection automotive diesel engine is experimentally investigated. In order to convert the pure dies...
متن کاملDo we expect most AGN to live in discs ? Philip
Recent observations have indicated that a large fraction of the lowto intermediate-luminosity AGN population lives in disc-dominated hosts, while the more luminous quasars live in bulgedominated hosts (that may or may not be major merger remnants), in conflict with some previous model predictions. We therefore build and compare a semi-empirical model for AGN fuelling which accounts for both mer...
متن کاملRed Giant–disk Encounters: Food for Quasars?
We explore the role that red giants might play in the fuelling and evolution of Active Galactic Nuclei. Due to their large radii and the low binding energy of the stellar envelope, giants are vulnerable to envelope stripping from collisions with the accretion disk. Using hydrodynamic simulations we show that such collisions will typically deposit a substantial fraction of the envelope mass into...
متن کامل