The interplay between radio-activity and the ISM in radio galaxies

Radio-loud AGNs can inhabit regions with a very rich ISM. The presence of this rich medium is likely related to the origin and evolution of the host galaxy and of the active nucleus. Recent observations show that a large fraction of radio galaxies contains a significant young stellar population. This supports the idea that mergers are responsible for both the starburst phase and the triggering of the nuclear activity. The gas that reaches the central regions can have quite disturbed kinematics, likely due to the effects of the AGN activity and in particular of the powerful radio jets. The recent detection of fast nuclear gas outflows, observed both in ionised and neutral gas, is giving new and important insights into the physical conditions of the gaseous medium around the nucleus and the interaction between the AGN and this medium. Finally, as another example of the interplay between the radio activity and the ISM, the possibility of star formation induced by the passage of the radio jet will be discussed.Comment: Invited paper to appear in the proceedings of IAU Symposium 222, The Interplay among Black Holes, Stars and ISM in Galactic Nuclei; Storchi Bergmann et al. eds. 6 pages, 3 figure

The Many Routes to AGN Feedback

The energy released by Active Galactic Nuclei (AGN) in the form of radiation, winds, or radio plasma jets, is known to impact on the surrounding interstellar medium. The result of these processes, known as AGN (negative) feedback, is suggested to prevent gas, in and around galaxies, from cooling, and to remove, or at least redistribute, gas by driving massive and fast outflows, hence playing a key role in galaxy evolution. Given its importance, a large effort is devoted by the astronomical community to trace the effects of AGN on the surrounding gaseous medium and to quantify their impact for different types of AGN. This review briefly summarizes some of the recent observational results obtained in different wavebands, tracing different phases of the gas. I also summarize the new insights they have brought, and the constraints they provide to numerical simulations of galaxy formation and evolution. The recent addition of deep observations of cold gas and, in particular, of cold molecular gas, has brought some interesting surprises and has expanded our understanding of AGN and AGN feedback.Comment: Invited review at the conference "Quasars at all cosmic epochs", published in Frontiers in Astronomy and Space Sciences, open access (https://doi.org/10.3389/fspas.2017.00042), 17 pages, 4 figure

Archaeology of active galaxies across the electromagnetic spectrum

Analytical and numerical galaxy-formation models indicate that active galactic nuclei (AGNs) likely play a prominent role in the formation and evolution of galaxies. However, quantifying this effect requires knowledge of how the nuclear activity proceeds throughout the life of a galaxy, whether it alternates with periods of quiescence and, if so, on what timescales these cycles occur. This topic has attracted growing interest, but making progress remains a challenging task. For optical and radio AGNs, a variety of techniques are used to perform a kind of "archaeology" that traces the signatures of past nuclear activity. Here we summarize recent findings regarding the lifecycle of an AGN from optical and radio observations. The limited picture we have so far suggests that these cycles can range from long periods of 10^7-10^8 yr to shorter periods of 10^4-10^5 yr, even reaching extreme events on timescales of just a few years. Together with simulations, observational results regarding the multiple cycles of AGN activity help to create a complete picture of the AGN lifecycle.Comment: Invited Review for Nature Astronomy, Aug 28 issue. 10 pages, 8 figure

Questions and challenges of what powers galactic outflows in active galactic nuclei

Different mechanisms can drive outflows in active galactic nuclei (AGN), but it is often unclear which mechanism dominates, if any. To quantify the impact of AGN feedback on galaxy evolution, the driving mechanism of outflows must be better understood.Comment: Authors' version of Nature Astronomy Comment. View-only version of full text publicly available at this link: http://rdcu.be/HUU

Cold and Warm Gas Outflows in Radio AGN

The study of the conditions and the kinematics of the gas in the central region of AGN provides important information on the relevance of feedback effects connected to the nuclear activity. Quantifying these effects is key for constraining galaxy evolution models. Here we present a short summary of our recent efforts to study the occurrence and the impact of gas outflows in radio-loud AGN that are in their first phase of their evolution. Clear evidence for AGN-induced outflows have been found for the majority of these young radio sources. The outflows are detected both in (warm) ionized as well in (cold) atomic neutral gas and they are likely to be driven (at least in most of the cases) by the interaction between the expanding jet and the medium. The mass outflow rates of the cold gas (HI) appear to be systematically higher than those of the ionized gas. The former reach up to ~50 Msun/yr, and are in the same range as "mild" starburst-driven superwinds in ULIRGs, whilst the latter are currently estimated to be a few solar masses per year. However, the kinetic powers associated with these gaseous outflow are a relatively small fraction (a few x 10^-4) of the Eddington luminosity of the galaxy. Thus, they do not appear to match the requirements of the galaxy evolution feedback models.Comment: Invited talk, to appear in the Proceedings of the IAU Symposium 267, "Co-Evolution of Central Black Holes and Galaxies", B.M. Peterson, R.S. Somerville, T. Storchi-Bergmann, eds., in pres

Interaction and gas outflows in radio-loud AGN - Disruptive and constructive effects of radio jets

In the last years, Active Galactic Nuclei (AGN) have become more popular than ever. The possibility of using them to produce feedback effects that would help solving some of the still open questions connected to the hierarchical scenario of galaxy formation and evolution, has made them particularly popular among theorists. AGN-driven outflows can have different origin. Here, I will concentrate on the role that the radio-loud phase of nuclear activity (and the presence of radio plasma jets) can play in the evolution of a galaxy. I will focus on two aspects in which radio activity could be important. The first is exploring whether relativistic plasma jet associated with radio-loud galaxies could provide an effective way to produce gas outflows with characteristics that can be relevant in the evolution of the host galaxy. The second, is to investigate whether they can provide a mechanism for the triggering of star formation.Comment: Invited talk, to appear in the Proceedings of "AGN Feedback in Galaxy Formation", V.Antonuccio-Delogu and J. Silk, eds., in pres