1,490 research outputs found
Bar resilience to flybys in a cosmological framework
Get PDFIt has been proposed that close interactions with satellite galaxies can significantly perturb the morphology of the main galaxy. However, the dynamics of an already formed bar following the interaction with the external environment has not been studied in detail in a fully cosmological context. In this work, analysing the cosmological zoom-in simulation Eris2k, we study the effects that a very unequal-mass flyby crossing the stellar disc has on the stability of the pre-existing bar. We characterize the evolution of the bar strength and length showing that the perturbation exerted by the flyby shuffles the orbits of stars for less than one Gyr. After this time, the bar shows a remarkable resilience, reforming with properties comparable to those it had before the interaction. Our work shows that close unequal-mass encounters, the most frequent interactions occurring during the evolution of cosmic structures, have (i) an overall minor impact on the global evolution of the bar in the long term, still (ii) the effect is destructive, and (iii) a very weak interaction is sufficient to dismantle a strong bar leading to its "apparent death". As a consequence, due to the non-negligible duration of the bar-less period, a fraction of observed spiral galaxies classified as non-barred could be prone to bar formation
External versus internal triggers of bar formation in cosmological zoom-in simulations
Get PDFThe 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
Super-critical accretion of medium-weight seed black holes in gaseous proto-galactic nuclei
No full textAccretion at sustained or episodic super-Eddington (SE) rates has been
proposed as a pathway to grow efficiently light seeds produced by Pop-III
stars. We investigate if SE accretion can be sustained onto a black hole (BH)
with ~M in the centre of a gas-rich proto-galaxy
at . We perform high-resolution smoothed-particle hydrodynamical
simulations, including two different sub-grid models for SE accretion, one
based on the slim disc paradigm, and one inspired by recent
radiation-magnetohydrodynamical simulations by Jiang and collaborators.
Radiative feedback has the form of a thermal dump to surrounding gas particles,
with the radiative efficiency being set according to the different SE accretion
models. We find that, in all simulations, star formation, BH feedback, and
interactions between clumps and the BH rapidly quench accretion after
1~Myr, irrespective of the sub-grid model used for accretion. Quenching
is stronger in the model based on the simulations of Jiang and collaborators
relative to the slim disc model because of its higher radiative efficiency. The
SE growth phase is always very brief, lasting a few 0.1~Myr. In the most
optimistic case, the BH reaches a mass of 10~M. We
extrapolate the final BH masses from to , assuming subsequent
galaxy mergers will replenish the gas reservoir and trigger new cycles of SE
accretion. We find that at most BH seeds would grow to
10~M, comparable to the mass of massive BHs in spiral
galaxies such as the Milky Way, but falling short of the mass of the
high-redshift quasars.Comment: 20 pages, 19 figures, 3 table
Non-isotropic feedback from accreting spinning black holes
No full textActive galactic nuclei (AGNs) are massive black holes (BHs) caught in the act of accreting gas at the centre of their host galaxies. Part of the accreting mass is converted to energy and released into the surrounding medium, in a process loosely referred to as AGN feedback. Most numerical simulations include AGN feedback as a sub-grid model, wherein energy or momentum (or both) is coupled to the nearby gas. In this work, we implement a new momentum-driven model in the hydrodynamics code GIZMO, in which accretion from large scales is mediated by a sub-grid accretion disc model, and gas particles are stochastically kicked over a bi-conical region, to mimic observed kinetic winds. The feedback cone’s axis can be set parallel either to the angular momentum of the gas surrounding the BH or to the BH spin direction, which is self-consistently evolved within the accretion-disc model. Using a circumnuclear disc (CND) as a test bed, we find that (i) the conical shape of the outflow is always visible and is weakly dependent on the launching orientation and aperture, resulting in comparable mass inflows and outflows; (ii) the cone’s orientation is also similar amongst our tests, and it is not always the same as the initial value, due to the interaction with the CND playing a crucial role in shaping the outflow; and (iii) the velocity of the outflow, instead, differs and strongly depends on the interplay with the CND
Black hole spin evolution in warped accretion discs
No full textMassive black holes (BHs) inhabiting galactic nuclei can be described by two parameters only, i.e. mass and spin, that change through cosmic time in response to accretion and merger events. While most numerical simulations accurately track the BH mass, spin evolution is rarely taken into account. In this work, we implement and validate a self-consistent sub-grid model for the evolution of the BH mass and spin via gas accretion in the hydrodynamics code GIZMO. The model assumes that accretion from resolved scales does not occur instantaneously, but is mediated by a sub-grid geometrically thin α-disc. After validating our model semi-analytically, we test it in an idealised environment consisting of a circumnuclear disc, where gas accretion on to the accretion disc is consistently determined by GIZMO. In the absence of any accretion-related feedback, the spin evolution closely traces that observed in the semi-analytical models, and depends on the free parameters of our implementation, such as the initial BH spin, angular momentum of the accretion disc, and radius at which the gas inflow circularises. In GIZMO, we also couple our model with the biconical-outflow model presented in a companion paper, wherein the feedback axis is always aligned with the BH spin. In this last case, the evolution of the central BH differs significantly from the previous cases, since the feedback process modifies the gas dynamics and its inflow rates from resolved scales. Such an interaction cannot be modelled by simple semi-analytical models and should be treated using full N-body hydrodynamical simulations
The role of bars on the dynamical-friction-driven inspiral of massive objects
Get PDFIn this paper, we systematically explore the impact of a galactic bar on the inspiral time-scale of a massive object (MO) within a Milky Way-like galaxy. We integrate the orbit of MOs in a multicomponent galaxy model via a semi-analytical approach that accounts for dynamical friction generalized to rotationally supported backgrounds. We compare the MO evolution in a galaxy featuring a Milky Way-like rotating bar to the evolution within an analogous axisymmetric galaxy without the bar. In agreement with previous studies, we find that the bar presence may significantly affect the inspiral, sometimes making it shorter by a factor of a few, and sometimes hindering it for a Hubble time. The erratic behaviour is mainly impacted by the relative phase at which the MO encounters the stronger bar-induced resonances. In particular, the effect of the bar is more prominent for initially in-plane, prograde MOs, especially those crossing the bar co-rotation radius or outer Lindblad resonance. In the barred galaxy, we find the sinking of the most massive MOs ( _ 10 7 . 5 M _) approaching the galaxy from large separations ( _ 8 kpc) to be most efficiently hampered. Neglecting the effect of global torques associated with the non-symmetric mass distribution is thus not advisable even within an idealized, smooth galaxy model; we further note that spiral patterns are unlikely to affect the inspiral due to their transient and fluctuating nature. We speculate that the sinking efficiency of massive black holes involved in minor galaxy mergers may be hampered in barred galaxies, making them less likely to host a gravitational wave signal accessible to low-frequency detectors
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
Myrcia ovata Cambess., Fl. Bras. Merid.
No full text5.12. Myrcia ovata Cambess., Fl. Bras. Merid. 2: 319. 1832 (type: "In silvis caeduis prope pagum Aldea de S. Pedro et praedium S. Jacinto in provinciae Rio de Janeiro ", Saint-Hilaire s.n., P). = Myrcia atropunctata Kiaersk, Enum. Myrt. Bras.: 68. 1893 (type: Rio de Janeiro, Glaziou 11982, C, R). Syn. nov.Published as part of Sobral, M., Souza, M. C., Mazine-Capelo, F. & Lucas, E., 2010, Nomenclatural notes on Brazilian Myrtaceae, pp. 51-58 in Phytotaxa 8 on page 56, DOI: 10.11646/phytotaxa.8.1.6, http://zenodo.org/record/489525
Drought impact on phellem development: identification of novel gene regulators and evidence of photosynthetic activity
No full textThis dataset contains the supplementary data (Figures and Tables) included in the manuscript "Drought impact on phellem development: identification of novel gene regulators and evidence of photosynthetic activity". Supplementary Figures includes additional data to support the manuscript, including plant growth and physiology measurements, histochemical analysis and accessory data from differential expression analysis. Supplementary Tables include primer sequences, lists of differentially expressed genes obtained using DESeq2 and Gene Ontology enrichment analysis obtained using GlueGO
Raw transcriptomic and phenotypic data is available in the following sources:
Raw reads: https://www.ebi.ac.uk/ena/browser/view/PRJEB66289
RNA-seq: https://www.ebi.ac.uk/biostudies/arrayexpress/studies/E-MTAB-13376
Morphophysiological and chlorophyl fluorescence data: https://doi.org/10.34636/DMPortal/D8LBXX
Code/Software:
The R script used for differential gene expression analysis is available on GitHub: https://github.com/pedro-mb/CorkOakRNAseq
Additional data is available from the corresponding author, Pedro M. Barros, upon reques
Land lease agreement between Dominguez Estate Company and Yoshiko Kwahara, 1941-1942
No full textAgreement for 10 acres of the M. R. Dominguez allotment in Rancho San Pedro from November 1, 1941 to October 31, 1942 and a yearly rent of $250. The document is signed by the lessee and the company
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