Search Results (2)

The dynamics of the merger of a dwarf disc galaxy with a massive spiral galaxy of the Milky Way type were studied in detail. The remnant of such interaction after numerous crossings of the satellite through the disc of the main galaxy was a compact stellar core, the characteristics of which were close to small compact elliptical galaxies (cEs) or large ultra-compact dwarfs (UCDs). Such transitional cE/UCD objects with an effective radius of 100–200 pc arise as a result of stripping the outer layers of the stellar core during the destruction of a dwarf disc galaxy. Numerical models of the satellite before interaction included baryonic matter (stars and gas) and dark mass. We used N-body to describe the dynamics of stars and dark matter, and we used smoothed-particle hydrodynamics to model the gas components of both galaxies. The direct method of calculating the gravitational force between all particles provided a qualitative resolution of spatial structures up to 10 pc. The dwarf galaxy fell onto the gas and stellar discs of the main galaxy almost along a radial trajectory with a large eccentricity. This ensured that the dwarf crossed the disc of the main galaxy at each pericentric approach over a time interval of more than 9 billion years. We varied the gas mass and the initial orbital characteristics of the satellite over a wide range, studying the features of mass loss in the core. The presence of the initial gas component in a dwarf galaxy significantly affects the nature of the formation and evolution of the compact stellar core. The gas-rich satellite gives birth to a more compact elliptical galaxy compared to the merging gas-free dwarf galaxy. The initial gas content in the satellite also affects the internal rotation in the stripped nucleus. The simulated cE/UCD galaxies contained very little gas and dark matter at the end of their evolution. Full article

We generalize the Thomas–Fermi approach to galaxy structure to include central supermassive black holes and find, self-consistently and non-linearly, the gravitational potential of the galaxy plus the central black hole (BH) system. This approach naturally incorporates the quantum pressure of the fermionic warm dark matter (WDM) particles and shows its full power and clearness in the presence of supermassive black holes. We find the main galaxy and central black hole magnitudes as the halo radius $r_h$, halo mass $M_h$, black hole mass $M_{BH}$, velocity dispersion $\sigma$, and phase space density, with their realistic astrophysical values, masses and sizes over a wide galaxy range. The supermassive black hole masses arise naturally in this framework. Our extensive numerical calculations and detailed analytic resolution of the Thomas–Fermi equations show that in the presence of the central BH, both DM regimes—classical (Boltzmann dilute) and quantum (compact)—do necessarily co-exist generically in any galaxy, from the smaller and compact galaxies to the largest ones. The ratio $\mathcal{R}\left(r\right)$ of the particle wavelength to the average interparticle distance shows consistently that the transition, $\mathcal{R}\simeq 1$, from the quantum to the classical region occurs precisely at the same point $r_A$ where the chemical potential vanishes. A novel halo structure with three regions shows up: in the vicinity of the BH, WDM is always quantum in a small compact core of radius $r_A$ and nearly constant density; in the region $r_A<r<r_i$ until the BH influence radius $r_i$, WDM is less compact and exhibits a clear classical Boltzmann-like behavior; for $r>r_i$, the WDM gravity potential dominates, and the known halo galaxy shows up with its astrophysical size. DM is a dilute classical gas in this region. As an illustration, three representative families of galaxy plus central BH solutions are found and analyzed: small, medium and large galaxies with realistic supermassive BH masses of ${10}^5{M}_{\odot }$, ${10}^7{M}_{\odot }$ and ${10}^9{M}_{\odot }$, respectively. In the presence of the central BH, we find a minimum galaxy size and mass $M_h^{min}\simeq {10}^7{M}_{\odot }$, larger ($2.2233\times {10}^3$ times) than the one without BH, and reached at a minimal non-zero temperature $T_{min}$. The supermassive BH heats up the DM and prevents it from becoming an exactly degenerate gas at zero temperature. Colder galaxies are smaller, and warmer galaxies are larger. Galaxies with a central black hole have large masses $M_h>{10}^7{M}_{\odot }>M_h^{min}$; compact or ultracompact dwarf galaxies in the range ${10}^4{M}_{\odot }<M_h<{10}^7{M}_{\odot }$ cannot harbor central BHs. We find novel scaling relations $M_{BH}=D{M}_h^{\frac{3}{8}}$ and $r_h=C{M}_{BH}^{\frac{4}{3}}$, and show that the DM galaxy scaling relations $M_h=b{\Sigma }_0{r}_h^2$ and $M_h=a{{\sigma }_h}^4/{\Sigma }_0$ hold too in the presence of the central BH, ${\Sigma }_0$ being the constant surface density scale over a wide galaxy range. The galaxy equation of state is derived: pressure $P\left(r\right)$ takes huge values in the BH vicinity region and then sharply decreases entering the classical region, following consistently a self-gravitating perfect gas $P\left(r\right)={\sigma }^2\rho \left(r\right)$ behavior. Full article