We investigate effects of baryon dissipation on the dark matter virial scaling relation between total mass and velocity dispersion and the velocity bias of galaxies in groups and clusters using self-consistent cosmological simulations. We show that the baryon dissipation increases the velocity dispersion of dark matter within the virial radius by 5% - 10%. The effect is mainly driven by the change in density and gravitational potential in inner regions of cluster, and it is larger in lower mass systems where gas cooling and star formation are more efficient. We also show that the galaxy velocity bias depends on how galaxies are selected. Galaxies selected based on their stellar mass exhibit no velocity bias, while galaxies selected based on their total mass show positive bias of ~10%, consistent with previous results based on collisionless dark matter- only simulations. We further find that observational estimates of galaxy velocity dispersion are unbiased with respect to the velocity dispersion of dark matter, provided galaxies are selected using their stellar masses and and their velocity dispersions are computed with more than twenty most massive galaxies. Velocity dispersions estimated with fewer galaxies, on the other hand, can lead to significant underestimate of dynamical masses. Results presented in this paper should be useful in interpretating high-redshift groups and clusters as well as cosmological constraints derived from upcoming optical cluster surveys.
A specific modification of Newtonian dynamics known as MOND has been shown to reproduce the dynamics of most astrophysical systems at different scales without invoking non-baryonic dark matter (DM). There is, however, a long-standing unsolved problem when MOND is applied to rich clusters of galaxies in the form of a deficit (by a factor around two) of predicted dynamical mass derived from the virial theorem with respect to observations. In this article we approach the virial theorem using the velocity dispersion of cluster members along the line of sight rather than using the cluster temperatu…
We present joint Suzaku and Chandra observations of MKW4. With a global temperature of 1.6 keV, MKW4 is one of the smallest galaxy groups that have been mapped in X-rays out to the virial radius. We measure its gas properties from its center to the virial radius in the north, east, and northeast directions. Its entropy profile follows a power-law of $\propto r^{1.1}$ between R$_{500}$ and R$_{200}$ in all directions, as expected from the purely gravitational structure formation model. The well-behaved entropy profiles at the outskirts of MKW4 disfavor the presence of gas clumping or thermal no…
The patch like model of the hierarchical galaxy formation in the $Λ$CDM cosmological model with small damping scale is considered. In this model galaxies and clusters of galaxies are identified with rare high density peaks, what suppresses the action of random factors in the vicinity of peaks and makes the process of halos formation more rapid and regular. High concentration of irregular subhalos surrounding the central peaks and their subsequent merging just after formation allows to consider this medium as a mixture of collisionless dispersed dark matter (DM) particles and collisional subhal…
The Missing Baryons in the Milky Way and Local Group
银河系和所有其他星系都缺少大部分重子，因为已知的重子质量与引力质量之比（维里半径内）比WMAP确定的宇宙比小好几倍。这意味着要么重子从未落入星系，要么是强大的星系风带走了大部分重子。如果我们能够发现缺失的重子并测量其性质：空间分布、温度和金属丰度，就有可能区分这两种途径。星系中缺失的重子预计温度为1- 3E 6 K，因此需要X射线观测。在这篇白皮书中，我们展示了如何使用IXO等设备获得X射线观测，以识别和研究这些难以捉摸的重子。
We examine the evolution of non-relativistic cold dark matter gravitationally coupled to baryons with modes deep inside the Hubble radius (sub-horizon regime) using akinetic theory approach within the realm of Newtonian theory. We obtain the general solution for the total density perturbation and we also show that a baryon perturbation catches up with the dark matter perturbation at late times, which in turn makes possible the formation of bound structures. We extend the linear perturbation analysis by considering the turn-around event, the collapse of matter, and its virialization process.
Starting from the 1970s, some relations connecting dark matter and baryons were discovered, such as the Tully-Fisher relation. However, many of the relations found in galaxies are quite different from that found in galaxy clusters. Here, we report two new mysterious universal relations connecting dark matter and baryons in both galaxies and galaxy clusters. The first relation indicates that the total dynamical mass of a galaxy or a galaxy cluster $M_{500}$ has a power-law relation with its total baryonic mass $M_b$ within the `virial region': $M_{500} \propto M_b^a$, with $a \approx 3/4$. The …
The structure and assembly history of cluster-size haloes in Self-Interacting Dark Matter
我们执行暗物质的28个放松的大规模团簇大小的晕冷暗物质（CDM）和自相互作用暗物质（SIDM）模型的模拟，研究在大半径的模型之间的结构差异，重子物理的影响预计是非常有限的。我们发现，分布的径向轮廓的密度，椭球轴比，和速度各向异性（$β$）的晕之间的模型（在$\sim1σ$水平），即使在$\gtrsim10\%$的维里半径，如果自散射截面是$σ/m_χ=1$厘米$^2$ gr $^{-1}$的差异很大。直接与观测推断的密度剖面比较，不赞成$σ/m_χ=1$ cm $^2$ gr $^{-1}$的SIDM，但在中间径向范围（维里半径的$\sim3\%$），重子物理的影响是不确定的。在这个水平的横截面，我们发现一个较窄的$β$分布在SIDM，明显偏向各向同性轨道，没有SIDM（90\%的CDM）晕有$β>0.12$在$7\%$维里半径。我们估计，通过$\sim30$（$\sim10^{15}$ M $_\odot$）松弛集群的观测样本，一旦观测不确定性提高几倍，$β$就有可能用于对SIDM施加竞争约束。我们研究了SIDM团簇中晕组装历史记忆的抑制。对于$σ/m_χ=1$ cm $^2$ gr $^{-1}$，我们发现，这只发生在中央晕区（$\sim1/4$的规模半径的晕），并只为晕，组装其质量在此区域内早于形成红移$z_f\sim2$。除此之外，组装的记忆仍然存在，并以类似于CDM的方式…
In this work we aim at investigating the effects of baryons on the dark matter (DM) haloes structure, focusing on the correlation between the presence and importance of stellar discs and the halo shapes. We study the properties of a subsample of DM haloes from Fenix and EAGLE cosmological simulations. We inspect the central regions of haloes in the mass range [10.9 - 992.3] x 10^{10} Msun at z=0, comparing the hydrodynamic runs and their dark matter only (DMo) counterparts. Our results indicate that baryons have a significant impact on the shape of the inner halo, mainly within ~ 20 percent of…
流体通常具有耗散性。我们探讨耗散的形式，在冷的暗物质流体的体积粘度。我们用超新星、重子声学振荡和宇宙微波背景的当前数据来约束这个模型。仅考虑各向同性和均匀的背景，粘性暗物质允许具有体积粘度$\lesssim 10^7$ Pa $\cdot$ s，这也与预期的综合萨克斯-沃尔夫效应（这困扰着一些具有体积粘度的模型）一致。我们进一步研究了粘性暗物质晕的小规模形成，这证明了对暗物质粘度的明显更强的约束。矮星系的存在只有在暗物质的粘性值$\lesssim 10^{-3}$ Pa $\cdot$ s小得多的情况下才能得到保证。
We consider a dark matter halo (DMH) of a spherical galaxy as a Bose-Einstein condensate of the ultra-light axions interacting with the baryonic matter. In the mean-field limit, we have derived the integro-differential equation of the Hartree-Fock type for the spherically symmetrical wave function of the DMH component. This equation includes two independent dimensionless parameters: (i) \b{eta}- the ratio of baryon and axion total mases and (ii) ξ- the ratio of characteristic baryon and axion spatial parameters. We extended our dissipation algorithm for studying numerically the ground state of…
A critical dark matter halo mass ($M_{\rm crit}$) for Population III (Pop III) stars can be defined as the typical minimum halo mass that hosts sufficient cold dense gas required for the formation of the first stars. The presence of Lyman-Werner (UV) radiation, which can dissociate molecular hydrogen, and the baryon-dark matter streaming velocity both delay the formation of Pop III stars by increasing $M_{\rm crit}$. In this work, we constrain $M_{\rm crit}$ as a function of Lyman-Werner flux (including self-shielding), baryon-dark matter streaming, and redshift using cosmological simulations …
