The M_BH − M_star relation of obscured AGNs at high redshift

We report the detection of broad Hα emission in three X-ray selected obscured AGNs at z ∼ 1–2. By exploiting the Hα width and the intrinsic X-ray luminosity, we estimate their black hole masses, which are in the range 0.1–3 × 109 M⊙. By means of multi-band photometric data, we measure the stellar mass of their host galaxy and, therefore, infer their MBH/Mstar ratio. These are the first obscured AGNs at high-z, selected based on their black hole accretion (i.e. on the basis of their X-ray luminosity), that can be located on the MBH − Mstar relation at high-z. All of these obscured high-z AGNs are fully consistent with the local MBH − Mstar relation. This result conflicts with those for other samples of AGNs in the same redshift range, whose MBH/Mstar ratio departs significantly from the value observed in local galaxies. We suggest that the obscured AGNs in our sample are in an advanced evolutionary stage, have already settled onto the local MBH-Mstar relation, and whose nuclear activity has been temporarily revived by recent galaxy interactions.