Oral Presentation

Vibrationally excited lines as tracers of hidden AGN activity

Author(s): Francesco Costagliola (Chalmers), Jeff Mangum (NRAO), Susanne Aalto (Chalmers), Sergio Martin (ALMA)

Presenter: Francesco Costagliola (Chalmers University of Technology (Sweden))

The compact nuclei of obscured luminous infrared galaxies (LIRG) have been proposed to trace the early stages of AGN accretion and are thus key to our understanding of galaxy evolution. Because of the high extinction, the inner 100 pc of these objects are extremely difficult to study at wavelengths shorter than the millimeter. Recent observations reveal that even standard mm-wave dense gas tracers such as HCN are self-absorbed and that more optically thin tracers are needed (Martin 2016). In our pioneering studies with ALMA and the PdBI (Aalto 2015), we found that mm-wave emission from vibrationally excited molecules is associated with compact IR emission and can better trace the kinematics of the circumnuclear material. However at these wavelengths the interpretation of the observations is complicated by the high opacity. Absorption lines at lower frequencies could provide the much needed tracer of such obscured environments. Our pioneering studies in the obscured LIRG NGC4418 with the JVLA show that it is possible to detect vibrationally excited molecules in absorption but higher sensitivities are needed in order to trace the gas kinematics. ALMA Band 1 would provide the sensitivity and resolution to image vibrationally excited absorption of key dense gas tracers (e.g. HCN, HC3N) which has the potential to become a powerful tool for the study of obscured AGN.