AGN Feedback in local galaxies : a multiphase and multiscale perspective

The necessity of active galactic nuclei (AGN) feedback to shape galaxy evolution finds a general consensus in the astrophysics community, supported by both observational and theoretical evidence. However, the way in which the AGN feedback really operates and its impact on the star formation activity of host galaxies is far from being understood. The goal of this thesis is to investigate the AGN feedback mechanism in the local Universe by probing the impact of AGN activity, through gas outflows, on the star formation process across the galaxy disc. AGN driven outflows span a wide range of physical scales and affect different gas phases, from the cold and warm molecular ($\rm H_2$) and atomic (HI) to the warm ionized ($\rm H^+$) and hot X-ray emitting gas. However, to date, there are only a handful of sources for which multiphase and multiscale outflows have been constrained simultaneously. Therefore, this thesis aims at deriving the multiphase interstellar medium properties, kinematics, and outflow parameters in nearby active galaxies, by spanning physical scales from the inner tens of parsecs to ten of kiloparsecs from the central AGN. The analysis is performed by combining high resolution interferometric, integral field spectroscopic and imaging data from the radio, mm/submm, near- and mid-infrared up to the optical domain. In my Ph.D. thesis project, I first characterized the molecular and ionized gas phases by combining different tracers such as CO, [O III], \ha and \hd~emission lines. By modeling the gas kinematics, I was able to disentangle the AGN driven outflows from the ordered rotation disc motions and compare the outflow properties on the different physical scales and their contribution to total outflowing gas. \newline In the Seyfert galaxy Mrk 509 the cold molecular and warm ionized outflows overlap and show similar velocities suggesting a cooling sequence within a multiphase momentum-conserving wind driven by the AGN activity. Mrk 509 cold molecular gas fraction is consistent with that of local star-forming galaxies with the same stellar mass and its cold molecular gas disc is marginally stable against fragmentation. \newline Thanks to a multiband analysis of the nearby AGN NGC 2992 I was able to compare the cold molecular, warm ionized, and dust components simultaneously. The cold molecular and warm ionized gas discs are cospatial, but the outflow is multiphase only on $\sim$ 1 kpc scales. The ionized [O III] outflow extends from the nucleus out to 7 kpc with a maximum velocity of 1000 \kms in the inner 600 pc. The gas then slows to 200 \kms and the outflows becomes multiphase, with the bulk of the mass being carried by the cold molecular phase. On these scales, the multiphase wind seems to be associated with the radio bubbles. On scales above a few kpc, the wind is only detected in the ionized phase across the ionization cones. \newline One missing ingredient in this multiphase picture is the warm molecular gas that can be traced by both rotational and vibrational \hd~emission lines in the near-infrared. Before JWST, only a few works studied the warm molecular outflows. In this thesis, I tried to complete the picture of multiphase quasar-driven outflows in two type-2 qusars (QSO2s, namely J1430 and J1356) from the QSOFEED sample, by comparing the warm molecular measurements obtained in the near-infrared domain with VLT/SINFONI with the already available radio, mm/sub-mm and optical observations. In the J1430, the kinematics of the warm molecular gas is consistent with rotation but the warm \hd~position angle (PA) differs from the galaxy major axis, probably related to the ongoing merger and/or to the influence of the jet on the ionized and molecular gas. In J1356 only a fraction of the warm molecular gas is rotating and the kinematics is disturbed, but the CO and warm \hd~kinematics major axis are consistent, suggesting that are tracing the same disc. The warm gas shows higher velocity dispersion at the nucleus compared to the cold molecular gas, possibly related to differences in gas densities and temperatures. In both QSO2s high velocity outflowing gas is detected, however, the cold molecular phase dominates the mass budget. \newline A significant part of this thesis is then focused on the local variations of the molecular gas properties and on the star formation process across the galaxy disc. Indeed, these are two key ingredients of the baryon cycle in action in galaxies. The main goal is to assess whether the galaxies star formation is suppressed or triggered by AGN activity or if both processes can occur simultaneously. In particular, in the nearby luminous infrared galaxy NGC 7469 I investigated the correlations between PAH emission at 7.7 $\mu m$, SFR, and cold molecular gas mass on 300 pc spatial scales. PAHs correlate better with star formation than with the cold molecular mass, and the correlations become stronger closer to the nucleus. The correlation between the SFR and the cold molecular gas mass surface densities, the Kennicutt– Schmidt (KS) star formation law, of NGC 7469 exhibits an intermediate behavior to the K-S relations found for starburst galaxies and active galactic nuclei. \newline The resulting picture reflects the complexity of the AGN-galaxy interaction, which not only spans a wide range of physical scales and gas phases but also combines processes characterized by different time scales. A significant improvement in the results presented in this thesis can be achieved by extending this type of analysis to an unbiased sample of local active galaxies. High-resolution observations of the various gas phases would enable one to determine whether the gas phases involved in the outflows are co-spatial or occupy distinct regions and to accurately measure the outflow parameters. In particular, scaling relations between AGN, host galaxy, and AGN wind properties in unbiased samples are essential, even expanding the analysis to lower AGN luminosities. This could provide deeper insights into the role of the AGN feeding and feedback cycle in galaxy evolution.