1,721,044 research outputs found
Massive black hole binaries in circumlinear discs: orbital dynamics and gas accretion.
No full textmissin
Massive black hole and gas dynamics in mergers of galaxy nuclei – II. Black hole sinking in star-forming nuclear discs
No full textMergers of gas-rich galaxies are key events in the hierarchical built-up of cosmic structures, and can lead to the formation of massive black hole binaries. By means of high-resolution hydrodynamical simulations we consider the late stages of a gas-rich major merger, detailing the dynamics of two circumnuclear discs, and of the hosted massive black holes during their pairing phase. During the merger gas clumps with masses of a fraction of the black hole mass form because of fragmentation. Such high-density gas is very effective in forming stars, and the most massive clumps can substantially perturb the black hole orbits. After similar to 10 Myr from the start of the merger a gravitationally bound black hole binary forms at a separation of a few parsecs, and soon after, the separation falls below our resolution limit of 0.39 pc. At the time of binary formation the original discs are almost completely disrupted because of SNa feedback, while on pc scales the residual gas settles in a circumbinary disc with mass similar to 10(5) M-circle dot. We also test that binary dynamics is robust against the details of the SNa feedback employed in the simulations, while gas dynamics is not. We finally highlight the importance of the SNa time-scale on our result
Overlapping inflows as catalysts of AGN activity - II. Relative importance of turbulence and inflow-disc interaction
Full text linkThe main challenge for understanding the fuelling of supermassive black holes in active galactic nuclei is not to account for the source of fuel, but rather to explain its delivery from the boundaries of the black hole sphere of influence (10-100 pc) down to sub-parsec scales. In this work, we report on a series of numerical experiments aimed at exploring in further depth our model of 'overlapping inflow events' as catalysts for rapid accretion, seeding a turbulent field in the infalling gas. We initially set a gaseous shell in non-equilibrium rotation around a supermassive black hole. After infall, the shell stalls in a disc-like structure. A second shell is then set in either corotation or counterrotation with respect to the first and is let to impinge on the previously formed disc. We find that combined turbulence and overlap significantly enhance accretion in counterrotating inflows, while turbulence dominates for corotating inflows. The leftovers of overlapping inflows are warped nuclear discs, whose morphology depend on the relative orientation and angular momentum of the disc and the shell. Overlapping inflows leave observational signatures in the gas rotation curves
Dynamical evolution of massive perturbers in realistic multicomponent galaxy models I: implementation and validation
No full textGalaxies are self-gravitating structures composed by several components encompassing spherical, axial, and triaxial symmetry. Although real systems feature heterogeneous components whose properties are intimately connected, semi-analytical approaches often exploit the linearity of the Poisson’s equation to represent the potential and mass distribution of a multicomponent galaxy as the sum of the individual components. In this work, we expand the semi-analytical framework developed in Bonetti et al. (2020) by including both a detailed implementation of the gravitational potential of exponential disc (modelled with a sech2 and an exponential vertical profile) and an accurate prescription for the dynamical friction experienced by massive perturbers (MP) in composite galaxy models featuring rotating disc structures. Such improvements allow us to evolve arbitrary orbits either within or outside the galactic disc plane. We validate the results obtained by our numerical model against public semi-analytical codes as well as full N-body simulations, finding that our model is in excellent agreement to the codes it is compared with. The ability to reproduce the relevant physical processes responsible for the evolution of MP orbits and its computational efficiency make our framework perfectly suited for large parameter-space exploration studies
Bar formation as driver of gas inflows in isolated disc galaxies
Full text linkStellar bars are a common feature in massive disc galaxies. On a theoretical ground, the response of gas to a bar is generally thought to cause nuclear starbursts and, possibly, AGN activity once the perturbed gas reaches the central supermassive black hole. By means of high-resolution numerical simulations, we detail the purely dynamical effects that a forming bar exerts on the gas of an isolated disc galaxy. The galaxy is initially unstable to the formation of non-axisymmetric structures, and within ˜1 Gyr it develops spiral arms that eventually evolve into a central stellar bar on kpc scale. A first major episode of gas inflow occurs during the formation of the spiral arms while at later times, when the stellar bar is establishing, a low-density region is carved between the bar corotational and inner Lindblad resonance radii. The development of such `dead zone' inhibits further massive gas inflows. Indeed, the gas inflow reaches its maximum during the relatively fast bar-formation phase and not, as often assumed, when the bar is fully formed. We conclude that the low efficiency of long-lived, evolved bars in driving gas towards galactic nuclei is the reason why observational studies have failed to establish an indisputable link between bars and AGNs. On the other hand, the high efficiency in driving strong gas inflows of the intrinsically transient process of bar formation suggests that the importance of bars as drivers of AGN activity in disc galaxies has been overlooked so far. We finally prove that our conclusions are robust against different numerical implementations of the hydrodynamics routinely used in galaxy evolution studies
Detectability of gravitational waves from primordial black holes orbiting Sgr A*
No full textPrimordial black holes, allegedly formed in the very early Universe, have been proposed as a possible viable dark matter candidate. In this work we characterize the expected gravitational wave signal detectable by the planned space-borne interferometer LISA and the proposed next generation space-borne interferometer μAres arising from a population of primordial black holes orbiting Sgr A, the supermassive black hole at the Galactic Center. Assuming that such objects indeed form the entire diffuse mass allowed by the observed orbits of stars in the Galactic Center (4×103 M within a radius of 10-3 pc from Sgr A), under the simplified assumption of circular orbits and monochromatic mass function, we assess the expected signal in gravitational waves, either from resolved and nonresolved sources. We estimate a small but non negligible chance of 10% of detecting one single 1 M primordial black hole with LISA in a 10-year-long data stream, while the background signal due to unresolved sources would essentially elude any reasonable chance of detection. On the contrary, μAres, with a 3 orders-of-magnitude better sensitivity at 10-5 Hz, would be able to resolve 140 solar mass primordial black holes in the same amount of time, while the unresolved background should be observable with an integrated signal-To-noise ratio 100. Allowing the typical PBH mass to be in the range 0.01-10 M would increase LISA chance of detection to 40% towards the lower limit of the mass spectrum. In the case of μAres, instead, we find a "sweet spot"just about 1 M, a mass for which the number of resolvable events is indeed maximized
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
External versus internal triggers of bar formation in cosmological zoom-in simulations
No full textThe emergence of a large-scale stellar bar is one of the most striking features in disc galaxies. By means of state-of-the-art cosmological zoom-in simulations, we study the formation and evolution of bars in Milky Way-like galaxies in a fully cosmological context, including the physics of gas dissipation, star formation and supernova feedback. Our goal is to characterize the actual trigger of the non-axisymmetric perturbation that leads to the strong bar observable in the simulations at z = 0, discriminating between an internal/secular and an external/tidal origin. To this aim, we run a suite of cosmological zoom-in simulations altering the original history of galaxy-satellite interactions at a time when the main galaxy, though already bar-unstable, does not feature any non-axisymmetric structure yet. We find that the main effect of a late minor merger and of a close fly-by is to delay the time of bar formation and those two dynamical events are not directly responsible for the development of the bar and do not alter significantly its global properties (e.g. its final extension). We conclude that, once the disc has grown to a mass large enough to sustain global non-axisymmetric modes, then bar formation is inevitable
- …
