We present the latest determination of the X-ray (2-10 keV) AGN luminosity function accounting for the selection effect due to X-ray absorption. The main results are: 1) the inclusion of obscured AGN confirms the AGN differential luminosity evolution, but makes it less extreme than what is found selecting unobscured AGN in soft X-rays, and more similar to a pure luminosity evolution; 2) signifi...

Using the results of recent optical surveys we conclude that the non-detection of quasars down to faint magnitudes implies a significant flattening of the high redshift (z ∼ 6) optical active galactic nuclei (AGN) luminosity function for M1450 > −26.7. We find that all the data are consistent with a faint-end slope for the optical AGN luminosity function of β = −2.2 and β = −2.8, at the 90% and...

Hardness-intensity diagrams (HIDs) have been used with great success to study the accretion states and their connection to radio jets in X-ray binaries (XRBs). The analogy between XRBs and active galactic nuclei (AGN) suggests that similar diagrams may help to understand and identify accretion states in AGN and their connection to radio loudness. We construct “disc-fraction luminosity diagrams”...

Active Galactic Nuclei (AGN) are now known to be strong γ-ray emitters. After briefly describing AGN classification and the main ideas behind unified schemes, I summarize the main properties of blazars (that is BL Lacs and flatspectrum radio quasars) and their connection with relativistic beaming. Finally, I address the question of why blazars, despite being extreme and very rare objects, are t...

The recent Spitzer detections of the 9.7μm Si–O silicate emission in type 1 active galactic nuclei (AGN) provide support for the AGN unification scheme. The properties of the silicate dust are of key importance to understand the physical, chemical and evolutionary properties of the obscuring dusty torus around the AGN. Compared to that of the Galactic interstellar medium (ISM), the 10μm silicat...

Our current understanding of the physics of Active Galactic Nuclei AGN suggests that intense optical UV and X ray radiation elds should exist in the central regions of AGN These radiation elds are intense enough that high energy rays propagating through them are likely to pair produce and thus be absorbed before they can escape from the central source region of an AGN If the absorbed rays are s...

We have searched for neutral hydrogen (H I) in 95 active galaxies using the 100-meter Green Bank Telescope. The sample includes only nearby active galaxies up to 220 Mpc away (redshifts up to 0.05). Our galaxies all contain Seyfert active galactic nuclei (AGN) detected in the hard X-ray (14-195 keV) by the Swift Gamma-ray Burst satellite’s Burst Alert Telescope (BAT) 22-month survey. The hard X...

Direct correlations and a Principal Component Analysis (PCA) are presented for a complete sample of 110 soft X-ray selected AGN of which about half are Narrow-Line Seyfert 1 galaxies (NLS1s). The direct correlation analyses show that narrower FWHM(Hβ) correlates with steeper X-ray spectrum, stronger optical FeII emission, weaker [OIII] emission and stronger short-term X-ray variability. This di...

Over the last five decades, AGN studies have produced a number of spectacular examples of synergies and multifaceted approaches in astrophysics. The field of AGN research now spans the entire spectral range and covers more than twelve orders of magnitude in the spatial and temporal domains. The next generation of astrophysical facilities will open up new possibilities for AGN studies, especiall...

As a result of deep hard X-ray observations by Chandra and XMM-Newton a significant fraction of the cosmic X-ray background (CXRB) has been resolved into individual sources. These objects are almost all active galactic nuclei (AGN) and optical followup observations find that they are mostly obscured Type 2 AGN, have Seyfert-like X-ray luminosities (i.e., L X ∼ 10 43−44 ergs s −1), and peak in r...