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Added by
Dominique Eckert Dr.
Publication date
2021
fields
Physics
and research's language is
English
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The co-evolution between supermassive black holes and their environment is most directly traced by the hot atmospheres of dark matter halos. Cooling of the hot atmosphere supplies the central regions with fresh gas, igniting active galactic nuclei (AGN) with long duty cycles. Outflows from the central engine tightly couple with the surrounding gaseous medium and provide the dominant heating source preventing runaway cooling by carving cavities and driving shocks across the medium. The AGN feedback loop is a key feature of all modern galaxy evolution models. Here we review our knowledge of the AGN feedback process in the specific context of galaxy groups. Galaxy groups are uniquely suited to constrain the mechanisms governing the cooling-heating balance. Unlike in more massive halos, the energy supplied by the central AGN to the hot intragroup medium can exceed the gravitational binding energy of halo gas particles. We report on the state-of-the-art in observations of the feedback phenomenon and in theoretical models of the heating-cooling balance in galaxy groups. We also describe how our knowledge of the AGN feedback process impacts on galaxy evolution models and on large-scale baryon distributions. Finally, we discuss how new instrumentation will answer key open questions on the topic.
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In this study we quantify the properties of the gas and dark matter around active galactic nuclei (AGN) in simulated galaxy groups and clusters and analyze the effect of AGN feedback on the surrounding intra-cluster (group) medium. Our results suggest downsizing of AGN luminosity with host halo mass, supporting the results obtained from clustering studies of AGN. By examining the temperature and density distribution of the gas in the vicinity of AGN we show that due to feedback from the central engine, the gas gets displaced from the centre of the group/cluster resulting in a reduction of the density but an enhancement of temperature. We show that these effects are pronounced at both high and low redshifts and propose new observables to study the effect of feedback in higher redshift galaxies. We also show that the average stellar mass is decreased in halos in the presence of AGN feedback confirming claims from previous studies. Our work for the first time uses a fully cosmological-hydrodynamic simulation to evaluate the global effects of AGN feedback on their host dark matter halos as well as galaxies at scales of galaxy groups and clusters.
The remarkable progress made in infrared (IR) astronomical instruments over the last 10-15 years has radically changed our vision of the extragalactic IR sky, and overall understanding of galaxy evolution. In particular, this has been the case for the study of active galactic nuclei (AGN), for which IR observations provide a wealth of complementary information that cannot be derived from data in other wavelength regimes. In this review, I summarize the unique contribution that IR astronomy has recently made to our understanding of AGN and their role in galaxy evolution, including both physical studies of AGN at IR wavelengths, and the search for AGN among IR galaxies in general. Finally, I identify and discuss key open issues that it should be possible to address with forthcoming IR telescopes.
Active Galactic Nuclei (AGN) are energetic astrophysical sources powered by accretion onto supermassive black holes in galaxies, and present unique observational signatures that cover the full electromagnetic spectrum over more than twenty orders of magnitude in frequency. The rich phenomenology of AGN has resulted in a large number of different flavours in the literature that now comprise a complex and confusing AGN zoo. It is increasingly clear that these classifications are only partially related to intrinsic differences between AGN, and primarily reflect variations in a relatively small number of astrophysical parameters as well the method by which each class of AGN is selected. Taken together, observations in different electromagnetic bands as well as variations over time provide complementary windows on the physics of different sub-structures in the AGN. In this review, we present an overview of AGN multi-wavelength properties with the aim of painting their big picture through observations in each electromagnetic band from radio to gamma-rays as well as AGN variability. We address what we can learn from each observational method, the impact of selection effects, the physics behind the emission at each wavelength, and the potential for future studies. To conclude we use these observations to piece together the basic architecture of AGN, discuss our current understanding of unification models, and highlight some open questions that present opportunities for future observational and theoretical progress.
The metallicity of active galactic nuclei (AGNs), which can be measured by emission line ratios in their broad and narrow line regions (BLRs and NLRs), provides invaluable information about the physical connection between the different components of AGNs. From the archival databases of the International Ultraviolet Explorer, the Hubble Space Telescope and the Sloan Digital Sky Survey, we have assembled the largest sample available of AGNs which have adequate spectra in both the optical and ultraviolet bands to measure the narrow line ratio [N II]/H{alpha} and also, in the same objects, the broad-line N V/C IV ratio. These permit the measurement of the metallicities in the NLRs and BLRs in the same objects. We find that neither the BLR nor the NLR metallicity correlate with black hole masses or Eddington ratios, but there is a strong correlation between NLR and BLR metallicities. This metallicity correlation implies that outflows from BLRs carry metal-rich gas to NLRs at characteristic radial distances of ~ 1.0 kiloparsec. This chemical connection provides evidence for a kinetic feedback of the outflows to their hosts. Metals transported into the NLR enhance the cooling of the ISM in this region, leading to local star formation after the AGNs turn to narrow line LINERs. This post-AGN star formation is predicted to be observable as an excess continuum emission from the host galaxies in the near infrared and ultraviolet, which needs to be further explored.
Outflows from active galactic nuclei (AGN) are one of the fundamental mechanisms by which the central supermassive black hole interacts with its host galaxy. Detected in $ge 50%$ of nearby AGN, these outflows have been found to carry kinetic energy that is a significant fraction of AGN power, and thereby give negative feedback to their host galaxies. To understand the physical processes that regulate them, it is important to have a robust estimate of their physical and dynamical parameters. In this review we summarize our current understanding on the physics of the ionized outflows detected in absorption in the UV and X-ray wavelength bands. We discuss the most relevant observations and our current knowledge and uncertainties in the measurements of the outflow parameters. We also discuss their origin and acceleration mechanisms. The commissioning and concept studies of large telescope missions with high resolution spectrographs in UV/optical and X-rays along with rapid advancements in simulations offer great promise for discoveries in this field over the next decade.
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