Outflows in low luminosity active galactic nuclei

Résumé

This thesis is aimed to provide insights into the relevance of feedback processes in galaxies harbouring at its centre an Active Galactic Nucleus (AGN). Feedback is believed to impact the evolution of galaxies by regulating the star formation and AGN activity. In particular, these processes can be triggered by outflows, that are detected with various tracers related to different gas phases (e.g. ionised or hot gas). In this thesis, we focused on the exploration of the processes at the low end of the AGN luminosity function, in particular with Low- Ionisation Nuclear Emission-line Regions (LINERs). These objects are the largest AGN family in the Local Universe, representing more than 60% of the local population (Ho 2008). Their relative faintness make their detection and characterisation more difficult than for other AGN types, although their proximity gives these objects an advantage, since spatially resolved studies can be made. This is specially important for the characterisation of feedback processes, particularly in the search for outflows. During the last 20 years, outflows have been detected in a variety of systems, from starforming galaxies to AGNs. The increasing number of works dedicated to the study of feedback processes seem to conclude that outflows are ubiquitous in both types of galaxies. Many efforts now are dedicated to analysing their properties and evaluating their impact in the evolution of the host galaxy from pc to kpc-scales. However, in the case of AGNs their study has been mainly focused on luminous systems, where outflows are expected to be more powerful and thus easier to detect and characterise. Nevertheless, it remains unclear if outflows are also common or even ubiquitous in LINERs, as this AGN population has been largely unstudied. In this thesis we address this topic with three different methodologies that will be described along the corresponding chapters. Optical spectroscopy of type-2 LINERs. We first present the analysis of long-slit spectroscopic data for nine type-2 LINERs obtained with the Hubble Space Telescope (HST) and the Palomar Survey. This work complements the previous work by Cazzoli et al. (2018) on type-1 LINERs. The objectives are twofold: (i) detect a broad line region component in the Balmer emission lines, and (ii) search for outflows as a broad (σ ≤ 500 km s−1), blueshifted component in the emission lines. We detected a broad component for 67% of the HST spectra and 25% of the Palomar spectra. As for the outflows, we found that 35% of the type-2 LINERs are good candidates to host them. A search for ionised gas outflows in an Hα imaging atlas of nearby LINERs. We then systematically searched for outflows in a sample of 70 nearby LINERs by analysing the ionised gas distribution in these systems, using proprietary ALFOSC/NOT and archival HST narrow band imaging. We were able to identify the main morphologies of the Hα gas and detect possible outflows as extended gas for 32% of the objects. Afterwards, by combining imaging with kinematic data from the literature, we found that ∼50% of the local LINERs host an outflow in different gas phases. These results indicated that outflows are common in low luminosity AGNs as LINERs. Analysis of the candidate outflows in LINERs with MEGARA/GTC integral field spectroscopic data (IFS). Finally, we used IFS data to confirm or not the outflow candidates identified from the previous two works on a spatially-resolved basis. For that purpose we used MEGARA/GTC data of nine LINERs in three spectral bands in the optical range. We study as a first case the prototypical LINER NGC1052 (complementing with proprietary MUSE/VLT data). We detected in this object an ionised gas outflow probably driven by the jet, propagating in a region of turbulent gas, and triggering kpc-scale bubbles. Then we analysed the other eight objects, finding a kinematical signatures of an ionised gas outflow in four of these LINERs (i.e. 50%). The LINER NGC4438 is the only object in our sample for which we found three resolved kinematical components in all the emission lines with the MEGARA data. These probe the gaseous disc and an outflow with a bubble-like structure, previously detected with high spatial resolution imaging.