Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS, Eales et al. 2010). The detected $z>1$ objects are generally dusty galaxies with star formation rates $>10^2\, M_\odot$ yr$^{-1}$, occurring in a strongly dust-enshrouded environment and thus corresponding to FIR luminosity $L_{\rm FIR}>10^{12}\, L_\odot$.

Some of them show excess emission in the mid-IR (Negrello et al. 2014) if compared to the commonly used SEDs of galaxies with intense star formation. This excess may be accounted for by nuclear activity (Fritz et al. 2006), but the mid-IR data alone are not sufficient to draw firm conclusions about the presence of an AGN, let alone its characterization, because they indicate that AGNs, if present, are weak. Furthermore, the SED fitting requires photometric information over a broad spectral range without which the solutions might strongly depend on the used fitting templates.

On the one hand, high-resolution and sensitivity X-ray data might unambiguously confirm the presence or absence of a significant AGN emission. On the other, high-resolution and sensitivity mm-wavelengths data are precious to identify the dust and gas properties associated with both the star formation process and tracing the nuclear feeding and feedback processes dynamics. By combining them we can estimate the physical properties of the 