supermassive black holes

X-ray vs optical obscuration

Fotopoulou et al., 2016b, showcased the complex relation between X-ray and optical obscuration observed in AGN using the XXL-1000-AGN sample.

The left hand side of the plot shows the median spectral energy distribution (SED) of X-ray selected AGN, grouped by their X-ray obscuration. Indeed, the least X-ray obscured sources have on average a quasar-like power-law SED. On the other hand, very obscured X-ray sources (logNH>23) show passive-like optical colors and they reveal themselves as powerful AGN only in the mid-infrared. A more detailed look at the distribution of the optical obscuration on the right-hand side panel shows that even unobscured (logNH<21) sources could show high amounts of optical obscuration.

The evolution of agn in the 5-10 kev energy band

In Fotopoulou et al., 2016a we estimated for the first time the evolution of the X-ray luminosity function (XLF) of AGN in the 5-10 keV energy band.

The four panels show the evolution of the luminosity function at four redsfhit bins. The thin dashed lines show the XLF at redshift z=0 for reference. The XLF is transformed to the 2-10 keV energy range to allow a comparison with the literature. A numerous sample of 1,100 X-ray AGN and robust Bayesian analysis showed that the luminosity-dependent density evolution (LDDE) is the preferred model, while also posing some constraints on the bright slope of the XLF at high redshifts (z>3).

infrared colors of x-ray selected agn

Rovilos et al., 2011 discussed the optical and infrared properties of X-ray selected AGN.

The figure on the left shows the X-ray sources from the Lockman Hole Deep Field colored according to their X-ray obscuration. (blue: X-ray unobscored. hardness ratio<-0.4, red: X-ray obscured, harness ratio > -0.4). Their multiwavelength properties shown in this plot demonstrate that preferentially X-ray obscured AGN are also optical and mid-IR obscured. In addition, the open symbols show X-ray sources that fall outside the Stern et al., 2005 AGN selection criterion. These sources are lower luminosity AGN, with strong host contribution.