A new two-parametric family of mass distribution for spherical stellar systems is considered. It generalizes families by Kuzmin, Veltmann (1972) and by An, Evans (2006). Steady velocity dispersions are found for these models by solving an equation of hydrostatic equilibrium. Axisymmetric generalizations of the model are discussed.
Various solutions of the kinetic equation for the equilibrium of a gravitating sphere of uniform density with a quadratic gravitational potential and a linear dependence of gravitational force on radius are examined. New analytic solutions are obtained for a uniform sphere with a hollow spherical volume and central mass inside the sphere. Solutions are also obtained for an arbitrary number of spherical layers with the same density, but with different equilibrium distribution functions.
10,000 simulations of 1000-particle realisations of the same cluster are computed by direct force summation. Over three crossing times the original Poisson noise is amplified more than tenfold by self-gravity. The cluster's fundamental dipole mode is strongly excited by Poisson noise, and this mode makes a major contribution to driving diffusion of stars in energy. The diffusive flow through action space is computed for the simulations and compared with the predictions of both local-scattering theory and the Balescu-Lenard (BL) equation. The predictions of local-scattering theory are qualitati…
We carry out spherical Jeans modeling of nearly round pure-bulge galaxies selected from the ATLAS$^{\rm 3D}$ sample. Our modeling allows for gradients in the stellar mass-to-light ratio ($M_\star/L$) through analytic prescriptions parameterized with a `gradient strength' $K$ introduced to accommodate any viable gradient. We use a generalized Osipkov-Merritt model for the velocity dispersion (VD) anisotropy. We produce Monte Carlo sets of models based on the stellar VD profiles under both the $Λ$CDM and MOND paradigms. Here, we describe the galaxy data, the empirical inputs, and the modeling pr…
We present a new non-parametric Jeans code, GravSphere, that recovers the density $ρ(r)$ and velocity anisotropy $β(r)$ of spherical stellar systems, assuming only that they are in a steady-state. Using a large suite of mock data, we confirm that with only line-of-sight velocity data, GravSphere provides a good estimate of the density at the projected stellar half mass radius, $ρ(R_{1/2})$, but is not able to measure $ρ(r)$ or $β(r)$, even with 10,000 tracer stars. We then test three popular methods for breaking this $ρ-β$ degeneracy: using multiple populations with different $R_{1/2}$; using …
The vast majority of the mass in the Milky Way (MW) is in dark matter (DM); we therefore cannot directly observe the MW mass distribution, and have to use tracer populations in order to infer properties of the MW DM halo. However, MW halo tracers do not only feel the gravitational influence of the MW itself. Tracers can also be affected by MW satellites; Garavito-Camargo et al. (2019) (hereafter GC19) demonstrate that the Large Magellanic Cloud (LMC) induces a density wake in the MW DM, resulting in large scale kinematic patterns in the MW stellar halo. In this work, we use spherical harmonic …
Spherical stellar systems such as King models, in which the distribution function is a decreasing function of energy and depends on no other invariant, are stable in the sense of collisionless dynamics. But Weinberg showed, by a clever application of the matrix method of linear stability, that they may be nearly unstable, in the sense of possessing {\sl weakly} damped modes of oscillation. He also demonstrated the presence of such a mode in an $N$-body model by endowing it with initial conditions generated from his perturbative solution. In the present paper we provide evidence for the presenc…
Classification of Stellar Orbits in Axisymmetric Galaxies
众所周知，两个超大质量黑洞（SMBH）不能在哈勃时间内合并成一个球形星系;一个新兴的图片是，星系的几何形状，旋转和大的潜在扰动可能会引导SMBH通过临界三体散射阶段，并最终驱动SMBH合并。我们探讨了一个轻度扁平，非旋转，SMBH嵌入椭圆星系的N体模型内的轨道内容。当用作SMBH双星合并研究的基础时，黑洞绕过了在球形星系中经常看到的双星失速，并在Gyr时间尺度上合并（Khan et al. 2013）。使用频率映射和角动量的标准，我们确定了丰富的共振轨道的轴对称模型，包括飞碟，这是不存在的，否则相同的球形系统，并可能与二进制相互作用。我们量化了SMBH双星可能散射的轨道集，发现轴对称模型包含的这些潜在损失锥轨道的数量是我们等效的球形模型的近7倍。在这个扁平的模型中，这些轨道的质量大约是SMBH的3倍，这与SMBH双星需要散射到引力波状态是一致的。
We investigate the anisotropy of the stellar velocity dispersions within the effective radius, $R_{\rm e}$, in 24 ATLAS$^{\rm 3D}$ pure-bulge galaxies, 16 of which are kinematic slow rotators (SRs). We allow the spherical anisotropy parameter $β$ to be radially varying and allow a radial gradient in the stellar mass-to-light ratio ($M_\star/L$) through the parameter $K$ introduced earlier. The median anisotropy for SRs depends on $K$ as follows: $\langleβ_{\rm m}\rangle = a + b K$ with $a=0.19\pm 0.05$, $b=-0.13\pm 0.07$ ($Λ$CDM) or $a=0.21\pm 0.05$, $b=-0.26\pm 0.08$ (MOND), where $β_{\rm m}$…
Two sets of potential-density basis pairs for the study of radial perturbations in collisionless spherical stellar systems
Institute of Astronomy, Russian Academy of Sciences（俄罗斯科学院天文研究所）；Institute of Solar-Terrestrial Physics, Russian Academy of Sciences, Siberian Branch（俄罗斯科学院西伯利亚分院太阳-地球物理研究所）
GravSphere2: A higher-order Jeans method for mass-modeling spherical stellar systems
Instituto de Astrofísica de Canarias（加那利天体物理学研究所）；Universidad de La Laguna（拉古纳大学）；University of Surrey（萨里大学）；Leibniz-Institut für Astrophysik Potsdam (AIP)（波茨坦阿斯特rophysik列布尼茨研究所）；Universität Potsdam（波茨坦大学）
A recent observational study of haloes of nearby Milky Way-like galaxies shows that only half (four out of eight) of the current sample exhibits strong negative metallicity ([Fe/H]) gradients. This is at odds with predictions from hydrodynamical simulations where such gradients are ubiquitous. In this Letter, we use high resolution cosmological hydrodynamical simulations to study the [Fe/H] distribution of galactic haloes. We find that kinematically selected stellar haloes, including both in-situ and accreted particles, have an oblate [Fe/H] distribution. Spherical [Fe/H] radial profiles show …
