Nowadays, it is widely accepted that most galaxies undergo an active
phase in their evolution. The impact of the energy released by active
galactic nuclei (AGN) on the interstellar medium (ISM) of the host
galaxy has been proposed as a key mechanism responsible for regulating
star formation (SF). Dust grains, gas, and molecules are excellent
tracers of the SMBH-host-galaxy connection. The IR waveband is host to
numerous spectral features that serve as sensitive barometers of the
physical conditions in the ISM. These include dust features, organic
molecules such as Polycyclic Aromatic Hydrocarbons (PAHs), small
organic molecules, hydrogen, and water, which are now accessible with
JWST and ALMA.
In this talk, I will summarize our recent JWST work, demonstrating
that dust grains and organic molecules (from small hydrocarbons to
complex PAHs) are essential tools for: 1) tracing not only star
formation rates (SFR) but also AGN feedback from the innermost regions
to kpc scales, and 2) identifying deeply obscured galactic nuclei in
both nearby and distant galaxies.
Our recent findings indicate that nuclear PAH emission in AGN is
primarily dominated by neutral PAHs, in contrast to the ionized PAHs
in star-forming regions, which are less stable due to “Coulomb
explosions”. This trend has been recently confirmed in a larger sample
of AGN, and provides evidence that outflows even in Seyfert-like AGN
have a significant impact on the ionization state of the PAH
molecules. These results highlight the great potential of these
organic molecules in disentangling AGN feedback. Therefore, caution
must be applied when using PAH bands as SFR indicators in AGN, even at
kpc scales. New JWST observations also provide valuable insights into
the formation and destruction of PAHs, offering exciting opportunities
to understand the crucial role that other small organic molecules play
in ISM chemistry and their relationship with more complex molecules
such as PAHs.
