1,720,983 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...
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
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
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
Investigating the effects of fresh gas on the Active Galactic Nuclei luminosity of early- and late-type galaxies
Full text linkThe main fuelling processes for Active Galactic Nuclei (AGN) are currently unknown. Previous work showed that galaxies with a large kinematic misalignment between their stellar and gas reservoirs have a higher AGN fraction than galaxies without misalignment. Such misalignment is a strong indication of a past galaxy interaction or an external accretion event. In this work we use integral field spectroscopy data from the SAMI and MaNGA surveys to investigate the AGN luminosity as a function of kinematic misalignment angle. Our sample of AGN exhibit bolometric luminosities in the range 1040 to 1043 erg s−1, indicative of low to moderate luminosity AGN. We find no correlation between AGN luminosity as a function of misalignment for AGN host galaxies from both surveys. We find some differences between the AGN luminosity of early- and late-type AGN host galaxies (ETGs, LTGs). AGN in LTG hosts have a wider luminosity range, with most LTG hosts showing aligned stellar to gas kinematics. AGN in ETG hosts have a luminosity range that does not depend on misalignment angle, suggesting AGN in ETG hosts are consistent with being fuelled by external accretion events, irrespective of their stellar to gas kinematic misalignment. While all the AGN in ETGs in our sample are consistent with being activated and fuelled by external gas, the range of observed AGN luminosities is likely caused by secondary factors such as the amount of fresh gas brought into the galaxy by the external interaction
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
A Stellar Dynamical Mass for the Central Black Hole in MCG–06-30-15
No full textWe present the stellar dynamical (SD) mass of the central black hole in the nearby Seyfert galaxy MCG–06-30-15 using the Schwarzschild orbit-superposition method implemented in the open-source code FORSTAND . We obtained spatially resolved K -band nuclear stellar spectra for this galaxy with SINFONI on the Very Large Telescope. We extracted the bulk stellar kinematics using Gauss–Hermite (GH) parameterization of the line-of-sight velocity distributions. A multicomponent surface-brightness profile of the galaxy was determined from a Hubble Space Telescope medium-band V image. Our best-fit models indicate a black hole mass of M _BH = (4.4 ± 1.4) × 10 ^7 M _⊙ and a stellar mass-to-light ratio of M / L = (3.0 ± 0.3) M _⊙ / L _⊙ , within 1 σ confidence intervals. Our constraint on M _BH agrees with an upper limit on the mass from stellar dynamics based on the Jeans anisotropic modeling method, but is ∼10 times larger than the reported mass from reverberation mapping (RM). However, our best-fit M _BH may be systematically biased high due to the counterrotating disk in the nucleus of MCG–06-30-15 and the inability of the GH parameterization to fully describe such a complicated set of stellar kinematics. In addition, a dynamical M _BH value depends heavily on the assumed source distance, which is not yet accurately constrained for this galaxy. MCG–06-30-15 is only the fourth galaxy in which we can compare M _BH from SD modeling with that from RM. A direct comparison of M _BH allows us to identify and investigate the possible sources of bias associated with different mass measurement techniques, which may influence our understanding of black hole and galaxy coevolution across cosmological timescales
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