The HELLAS2XMM survey. XIII. Multi-component analysis of the spectral
  energy distribution of obscured AGN
  We combine near-to-mid-IR Spitzer data with shorter wavelength observations
(optical to X-rays) to get insights on the properties of a sample of luminous,
obscured Active Galactic Nuclei (AGN). We aim at modeling their broad-band
Spectral Energy Distributions (SEDs) in order to estimate the main parameters
related to the dusty torus. The sample comprises 16 obscured high-redshift
(0.9<z<2.1) xray luminous quasars (L_2-10 ~ 10^44 erg s-1) selected from the
HELLAS2XMM survey. The SEDs are described by a multi-component model including
a stellar component, an AGN component and a starburst. The majority (~80%) of
the sources show moderate optical depth (tau_9.7um<3) and the derived column
densities N_H are consistent with the xray inferred values (10^22 <N_H< 3x10^23
cm-2) for most of the objects, confirming that the sources are moderately
obscured Compton-thin AGN. Accretion luminosities in the range 5x10^44 < Lbol <
4x10^46 erg s-1 are inferred. We compare model luminosities with those obtained
by integrating the observed SED, finding that the latter are lower by a factor
of ~2 in the median. The discrepancy can be as high as an order of magnitude
for models with high optical depth (tau_9.7um=10). The ratio between the
luminosities obtained by the fitting procedure and from the observed SED
suggest that, at least for Type~2 AGN, observed bolometric luminosities are
likely to underestimate intrinsic ones and the effect is more severe for highly
obscured sources. Bolometric corrections from the hard X-ray band are computed
and have a median value of k_2-10kev ~ 20. The obscured AGN in our sample are
characterized by relatively low Eddington ratios (median lambda_Edd~0.08). On
average, they are consistent with the Eddington ratio increasing at increasing
bolometric correction (e.g. Vasudevan & Fabiam 2009).
