The end of the black hole dark ages and the origin of warm absorbers

We consider how the radiation pressure of an accreting supermassive black hole (SMBH) affects the interstellar medium around it. Much of the gas originally surrounding the hole is swept into a shell with a characteristic radius somewhat larger than the black hole's radius of influence (∼1–100 pc). The shell has a mass directly comparable to the (M-σ) mass that the hole will eventually reach, and may have a complex topology. We suggest that outflows from the central SMBHs are halted by collisions with the shell, and that this is the origin of the warm absorber components frequently seen in active galactic nucleus (AGN) spectra. The shell may absorb and reradiate some of the black hole accretion luminosity at long wavelengths, implying both that the bolometric luminosities of some known AGN may have been underestimated, and that some accreting SMBH may have escaped detection entirely.