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Register a new userDynamical evolution of massive perturbers in realistic multi-component galaxy models I: implementation and validation
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Galaxies 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 Poissons equation to represent the potential and mass distribution of a multi-component 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 ${rm sech}^2$ and an exponential vertical profile) and an accurate prescription for the dynamical friction experienced by massive perturbers 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 massive perturber orbits and its computational efficiency make our framework perfectly suited for large parameter-space exploration studies.
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In this paper, we explore the impact of a galactic bar on the inspiral time-scale of a massive perturber (MP) within a Milky Way-like galaxy. We integrate the orbit of MPs in a multi-component galaxy model via a semi-analytical approach including an accurate treatment for dynamical friction generalized to rotationally supported backgrounds. We compare the MP evolution in a galaxy featuring a Milky Way-like rotating bar to the evolution within an analogous axisymmetric galaxy without the bar. We find that the bar presence may significantly affect the inspiral, sometimes making it shorter by a factor of a few, sometimes hindering it for a Hubble time, implying that dynamical friction alone is greatly insufficient to fully characterize the orbital decay. The effect of the bar is more prominent for initially in-plane, prograde MPs, especially those crossing the bar co-rotation radius or outer Lindblad resonance. In the barred galaxy, we find the sinking of the most massive MPs (>~10^7.5 Msun) approaching the galaxy from large separations (>~8 kpc) to be most efficiently hampered. Neglecting the effect of global torques associated to the non-symmetric mass distribution is thus not advisable even within our idealized, smooth Milky Way model, and it should be avoided when dealing with more complex and realistic galaxy systems. This has important implications for the orbital decay of massive black holes in late-type spirals, the natural candidate sources to be detected with the Laser Interferometer Space Antenna (LISA).
Massive black holes (MBHs) are nowadays recognized as integral parts of galaxy evolution. Both the approximate proportionality between MBH and galaxy mass, and the expected importance of feedback from active MBHs in regulating star formation in their host galaxies point to a strong interplay between MBHs and galaxies. MBHs must form in the first galaxies and be fed by gas in these galaxies, with continuous or intermittent inflows that, at times, can be larger than the Eddington rate. Feedback from supernovae and from the MBHs themselves modulates the growth of the first MBHs. While current observational data only probe the most massive and luminous MBHs, the tip of the iceberg, we will soon be able to test theoretical models of MBH evolution on more normal MBHs: the MBHs that are indeed relevant in building the population that we observe in local galaxies, including our own Milky Way.
We present a significantly improved version of our numerical code JASMINE, that can now solve the Jeans equations for axisymmetric models of stellar systems, composed of an arbitrary number of stellar populations, a Dark Matter halo, and a central Black Hole. The stellar components can have different structural (density profile, flattening, mass, scale length), dynamical (rotational support, velocity dispersion anisotropy), and population (age, metallicity, Initial Mass Function, mass-to-light ratio) properties. These models, when combined with observations, will allow to investigate important issues, such as quantifying the systematic effects of IMF variations, of mass-to-light ratio gradients, and of different stellar kinematic components (e.g. counter rotating disks, kinematically decoupled cores) on luminosity-weighted properties. The developed analytical and numerical framework aims at modeling Early-Type Galaxies, but it can also be applied to dwarf Spheroidal galaxies and Globular Clusters.
We analyse the demographics of black holes (BHs) in the large-volume cosmological hydrodynamical simulation Horizon-AGN. This simulation statistically models how much gas is accreted onto BHs, traces the energy deposited into their environment and, consequently, the back-reaction of the ambient medium on BH growth. The synthetic BHs reproduce a variety of observational constraints such as the redshift evolution of the BH mass density and the mass function. Strong self-regulation via AGN feedback, weak supernova feedback, and unresolved internal processes result in a tight BH-galaxy mass correlation. Starting at z~2, tidal stripping creates a small population of BHs over-massive with respect to the halo. The fraction of galaxies hosting a central BH or an AGN increases with stellar mass. The AGN fraction agrees better with multi-wavelength studies, than single-wavelength ones, unless obscuration is taken into account. The most massive halos present BH multiplicity, with additional BHs gained by ongoing or past mergers. In some cases, both a central and an off-centre AGN shine concurrently, producing a dual AGN. This dual AGN population dwindles with decreasing redshift, as found in observations. Specific accretion rate and Eddington ratio distributions are in good agreement with observational estimates. The BH population is dominated in turn by fast, slow, and very slow accretors, with transitions occurring at z=3 and z=2 respectively.
A detailed model of the tidal disruption events (TDEs) has been constructed using stellar dynamical and gas dynamical inputs that include black hole (BH) mass $M_{bullet}$, specific orbital energy $E$ and angular momentum $J$, star mass $M_{star}$ and radius $R_{star}$, and the pericenter of the star orbit $r_{p}(E,hspace{1mm}J,hspace{1mm}M_{bullet})$. We solved the steady state Fokker--Planck equation using the standard loss cone theory for the galactic density profile $rho (r) propto r^{-gamma}$ and stellar mass function $xi(m) $ where $m=M_{star}/M_{odot}$ and obtained the feeding rate of stars to the BH integrated over the phase space as $dot{N}_{t} propto M_{bullet}^beta$, where $beta= -0.3pm 0.01$ for $M_{bullet}>10^7 M_{odot}$ and $sim 6.8 hspace{1mm} times 10^{-5}$ Yr$^{-1}$ for $gamma=0.7$. We use this to model the in-fall rate of the disrupted debris, $dot{M}(E,hspace{1mm}J,hspace{1mm}m,hspace{1mm}t)$, and discuss the conditions for the disk formation, finding that the accretion disk is almost always formed for the fiduciary range of the physical parameters. We also find the conditions under which the disk formed from the tidal debris of a given star with a super Eddington accretion phase. We have simulated the light curve profiles in the relevant optical g band and soft X-rays for both super and sub-Eddington accretion disks as a function of $dot{M}(E,hspace{1mm}J,hspace{1mm}t)$. Using this, standard cosmological parameters, and mission instrument details, we predict the detectable TDE rates for various forthcoming surveys finally as a function of $gamma$.
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