Multiple and Dual AGN systems

Almost every massive galaxy is assumed to host a super-massive black hole (SMBH) at its center. Considering  that our standard cosmological picture implies the hierarchical growth of galaxies through mergers, it is clear that also SMBH must eventually merge. These events are predicted to emit the most strongest gravitational waves that can be eventually detected with current or planned facitilies. It is therefore important to characterize the evolution of merging SMBHs  from large separation before coalesence on pc scales. Since it is difficult to directly observe SMBH it is much easier to recognize them if both SMBH are active and appearing as AGN. However, AGN have a time scale of a few Myr at most which makes is rather unlikely that both SMBH are active at the same time. The number of confirmed dual or binary AGN is therefore very small.

 

Understanding the nature of double-peaked AGN with 3D spectroscopy

Potential candidates for close AGN can be identified as so-called "double-peaked AGN" which exhibits two distinct peaks in the forbidden lines of the NLR, mainly [OIII]. Those can be easily detected in large spectroscopic surveys such as SDSS. Unfortunately, the NLR can have very complex kinematic structures caused by AGN driven outflows, illumination of companion galaxies by a single AGN, or rotating gas discs around the galaxy centre. Thus, their nature is not unique and needs to verified as a likely dual AGN. Optical or AO-assited NIR spectroscopy are ideal tools to constrain the nature of double-peaked AGN in many studies. I have also been involved in recent works to characterize those double-peaked AGN. In Woo et al. (2014) we studied a luminous double-peaked obscured QSO at redshift (z~0.35) with the VLT-VIMOS integral field unit. The bright optical [OIII] line is clearly split into two distinct velocity components and we were able to pin-point the spatial location of both components using spectro-astrometry. Both knots in [OIII] are matching exactly the two nuclei of the merging host galaxy separated by less than 1 kpc (see Figure below).  We are currently extinding those studies to other double-peaked AGN and also applying AO-assisted NIR IFU spectroscopy to increase the spatial resolution if possible.

Multiple AGN Activity (MAGNA) Project