1,721,002 research outputs found
Tracing the External Origin of the AGN Gas Fueling Reservoir
No full textNear-infrared observations of the active galaxy MCG–6-30-15 provide strong evidence that its molecular gas fueling reservoir is of external origin. MCG–6-30-15 has a counter-rotating core of stars within its central 400 pc and a counter-rotating disc of molecular gas that extends as close as ~50–100 pc from the central black hole. The gas counter-rotation establishes that the gas reservoir in the center of the galaxy originates from a past external accretion event. In this contribution we discuss the gas and stellar properties of MCG–6-30-15, its past history and how the findings on this galaxy can be used to understand AGN fueling in S0 galaxies with counter-rotating structures
An increase in black hole activity in galaxies with kinematically misaligned gas
No full textExternal accretion events such as a galaxy merger or the accretion of gas from the immediate environment of a galaxy can create a large misalignment between the gas and the stellar kinematics. Numerical simulations have suggested that misaligned structures may promote the inflow of gas to the nucleus of the galaxy and the accretion of gas by the central supermassive black hole. We show for the first time that galaxies with a strong misalignment between the ionized gas and stellar kinematic angles have a higher observed fraction of active black holes than galaxies with aligned rotation of gas and stars. The increase in black hole activity suggests that the process of formation and/or the presence of misaligned structures are connected with the fuelling of active supermassive black holes
AGN properties in a cosmological evolution scenario
No full textTo understand how AGN accrete, evolve and affect the surrounding galaxy, it is necessary to investigate how their intrinsic properties change with time. We consider different AGN populations, accounting for the physical properties and obscuration, and trace their redshift evolution. In particular, we investigate the role of Eddington ratio and accretion efficiency in the black hole mass function, and build a scenario where objects with a high spread in Eddington ratios, including low values (10-3-10-2) are consistent with the observed local mass function...
External gas accretion provides a fresh gas supply to the active S0 galaxy NGC 5077
No full textIn early-type galaxies, externally accreted gas is thought to be the main source of gas replenishment at late times. We use MUSE integral field spectroscopy data to study the active S0 galaxy NGC 5077, which is known to have disturbed dynamics that are indicative of a past external interaction. We confirm the presence of a stellar kinematically distinct core with a diameter of 2.8 kpc that is counter-rotating with respect to the main stellar body of the galaxy. We find that the counter-rotating core consists of an old stellar population that is not significantly different from the rest of the galaxy. The ionised gas is strongly warped and extends out to 6.5 kpc in the polar direction and in a filamentary structure. The gas dynamics is complex, with significant changes in the position angle as a function of radius. The ionised gas line ratios are consistent with LINER excitation by the active galactic nucleus, both in the nucleus and at kiloparsec scales. We discover a nuclear outflow with projected velocity V ∼ 400 km s−1, consistent with a hollow outflow cone intersecting the plane of the sky. The properties of the misaligned gas match predictions from numerical simulations of misaligned gas infall after a gas-rich merger. The warp and change in the gas orientation as a function of radius are consistent with gas relaxation due to stellar torques; these are stronger at small radii where the gas aligns faster than in the outer regions, driving gas to the nucleus. The stellar and gas dynamics indicate that NGC 5077 has had at least two external interactions, one that resulted in the formation of the counter-rotating core, followed by the second, late-time external gas accretion. NGC 5077 illustrates the importance of external interactions in the replenishment of the galaxy gas reservoir and the nuclear gas content available for black hole fuelling
Gas flows in a changing-look AGN
No full textThe galaxy Mrk 590 is one of the few known 'changing-look' Active Galactic Nuclei (AGN) to have transitioned between states twice, having just increased its flux after a period of ∼ 10 years of low activity. In addition to the increase in flux, the optical broad emission lines have reappeared but show a different profile than what was observed before they disappeared. The gas motions in the host galaxy of this changing-look AGN show outflows and dynamical structures able to drive gas to the nucleus, suggesting an interplay between inflow and outflow in the centre of the galaxy.</p
Stellar-gas kinematic misalignments in eagle: enhanced SMBH growth in misaligned galaxies
No full textStellar-gas kinematic misalignments are a transient phenomenon observed in ∼11 per cent of the local galaxy population. According to current models, misaligned gas is expected to lose angular momentum and relax into the galactic plane on timescales of ∼0.1 Gyr, driving gas toward the central regions of the galaxy. Recent observational studies have found a higher incidence of active galactic nuclei in misaligned galaxies. We use the eagle simulation to explore the connection between stellar-gas misalignments and enhanced central black hole (BH) activity between 0 < z < 1. We use a sample of ∼5600 galaxies with a stellar mass of M* ≥ 109.5 M⊙ that feature long-lived stellar-gas alignment, counter-rotation, and unstable misalignments (non-coplanarity). Over time windows of 0.5 Gyr, we find that galaxies experiencing an unstable misalignment have systematically enhanced BH growth during relaxation. Galaxies with long-term counter-rotation show little difference in BH growth compared to aligned galaxies. We suggest that this enhanced BH growth is driven by loss of angular momentum in unstable misaligned gas discs which is able to drive gas inward toward the vicinity of the BH. At z = 0.1, we find a greater incidence of overmassive BHs in galaxies that have spent a greater fraction of time with unstable stellar-gas kinematic misalignments over the preceding ≈2 Gyr compared to control samples of aligned galaxies. In agreement with observations, we conclude that BH activity is enhanced in misaligned systems in eagle and suggest that the presence of overmassive BHs may be indicative of a past stellar-gas kinematic misalignment
Mapping the active galactic nucleus effects on the stellar and gas properties of NGC 5806
No full textIt is commonly accepted that active galactic nuclei (AGNs) have a strong impact upon the evolution of their host galaxies, but the processes by which they do so are not fully understood. We aim to further the understanding of AGN feeding and feedback by examining an active galaxy using spatially resolved spectroscopy. We analyze integral field spectroscopy of the active galaxy NGC 5806, obtained using the Very Large Telescope Multi-Unit Spectroscopic Explorer. We map the dynamics of gas and stars, as well as gas optical emission line fluxes throughout the central 8 × 8 kpc2 of the galaxy. We use emission line ratios to map gas metallicity and identify regions of gas excitation dominated by AGN/shocks or star formation. We also determine the average stellar population age and metallicity, and model the rotation and dynamics of the galaxy. We find that NGC 5806 has a star-forming circumnuclear ring, with a projected radius of ~400 pc. The dynamics of this galaxy are driven by a large-scale bar, which transports gas from the spiral arm to the central ring and potentially fuels the AGN. We also observe AGN-dominated gas excitation up to 3.3 kpc away from the center of the galaxy, showing the extended AGN effect on the gas in the central regions of the galaxy
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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