We use highly spectroscopically complete deep and wide-area Chandra surveys to determine the cosmic evolution of hard X-ray–selected AGNs .
For the deep fields , we supplement the spectroscopic redshifts with photometric redshifts to assess where the unidentified sources are likely to lie .
We find that the median redshifts are fairly constant with X-ray flux at z \sim 1 .
We classify the optical spectra and measure the FWHM line widths .
Most of the broad-line AGNs show essentially no visible absorption in X-rays , while the sources without broad lines ( { FWHM } < 2000 km s ^ { -1 } ; “ optically-narrow ” AGNs ) show a wide range of absorbing column densities .
We determine hard X-ray luminosity functions for all spectral types with L _ { X } \geq 10 ^ { 42 } ergs s ^ { -1 } and for broad-line AGNs alone .
At z < 1.2 , both are well described by pure luminosity evolution , with L _ { \ast } evolving as ( 1 + z ) ^ { 3.2 \pm 0.8 } for all spectral types and as ( 1 + z ) ^ { 3.0 \pm 1.0 } for broad-line AGNs alone .
Thus , all AGNs drop in luminosity by almost an order of magnitude over this redshift range .
We show that this observed drop is due to AGN downsizing rather than to an evolution in the accretion rates onto the supermassive black holes .

We directly compare our broad-line AGN hard X-ray luminosity functions with the optical QSO luminosity functions and find that at the bright end they agree extremely well at all redshifts .
However , the optical QSO luminosity functions do not probe faint enough to see the downturn in the broad-line AGN hard X-ray luminosity functions and even appear to be missing some sources at the lowest luminosities they probe .

We find that broad-line AGNs dominate the number densities at the higher X-ray luminosities , while optically-narrow AGNs dominate at the lower X-ray luminosities .
We rule out galaxy dilution as a partial explanation for this effect by measuring the nuclear UV/optical properties of the Chandra sources using the HST ACS GOODS-North data .
The UV/optical nuclei of the optically-narrow AGNs are much weaker than expected if the optically-narrow AGNs were similar to the broad-line AGNs .
We therefore postulate the need for a luminosity dependent unified model .
An alternative possibility is that the broad-line AGNs and the optically-narrow AGNs are intrinsically different source populations .
We cover both interpretations by constructing composite spectral energy distributions—including long-wavelength data from the mid-infrared to the submillimeter—by spectral type and by X-ray luminosity .
We use these spectral energy distributions to infer the bolometric corrections ( from hard X-ray luminosities to bolometric luminosities ) needed to map the accretion history .

We determine the accreted supermassive black hole mass density for all spectral types and for broad-line AGNs alone using the observed evolution of the hard X-ray energy density production rate and our inferred bolometric corrections .
We find that only about one-half to one-quarter of the supermassive black hole mass density was fabricated in broad-line AGNs .
Using either recent optical QSO luminosity function determinations or our broad-line AGN hard X-ray luminosity function determinations , we measure an accreted supermassive black hole mass density that is a factor of almost two lower than that measured by previous work , assuming \epsilon = 0.1 .
This leaves room for the obscured accretion when compared with the local supermassive black hole mass density .
In fact , we find reasonable agreement between the accreted supermassive black hole mass density from all spectral types and the local supermassive black hole mass density , assuming \epsilon \approx 0.1 - 0.2 .
However , there is very little room for further obscured sources or for any low efficiency accretion periods .