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.
The baryon content around local galaxies is observed to be much less than is needed in Big Bang nucleosynthesis. Simulations indicate that a significant fraction of these "missing baryons" may be stored in a hot tenuous circum-galactic medium (CGM) around massive galaxies extending to or even beyond the virial radius of their dark matter halos. Previous observations in X-ray and Sunyaev-Zel'dovich (SZ) signal claimed that $\sim(1-50)\%$ of the expected baryons are stored in a hot CGM within the virial radius. The large scatter is mainly caused by the very uncertain extrapolation of the hot gas…
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…
Formation of halos in the Dark Ages from initial spherical perturbations is analyzed in a four component Universe (dark matter, dark energy, baryonic matter and radiation) in the approximation of relativistic hydrodynamics. Evolution of density and velocity perturbations of each component is obtained by integration of a system of nine differential equations from $z=10^8$ up to virialization, which is described phenomenologically. It is shown that the number density of dark matter halos with masses $M\sim10^8-10^9\,\mathrm{M_{\odot}}$ virialized at $z\sim10$ is close to the number density of ga…
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…
We survey the highly ionized circumgalactic media (CGM) of 29 blindly selected galaxies at 0.49 < z_(gal) < 1.44 based on high-S/N ultraviolet spectra of z > 1 QSOs and the galaxy database from the COS Absorption Survey of Baryon Harbors (CASBaH). We detect the Ne VIII doublet in nine of the galaxies, and for gas with N(Ne VIII) > 10^13.3 cm^-2 (> 10^13.5 cm^-2), we derive a Ne VIII covering fraction f_c = 75 +15/-25% (44 +22/-20%) within impact parameter (rho) < 200 kpc of M_* = 10^(9.5-11.5) Msol galaxies and f_c = 70 +16/-22% (f_c = 42 +20/-17%) within rho < 1.5 virial radii. We estimate th…
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 …
By means of interferometic 21-cm observations and a 3D kinematic modeling technique, we study the gas kinematics of six HI-rich ultra-diffuse galaxies (UDGs). We derive robust circular velocities and baryonic masses, that allow us to study the position of our UDGs with respect to the baryonic Tully-Fisher relation (BTFR). Somewhat surprisingly, we find that these galaxies are strong outliers from the BTFR, rotating too slowly for their baryonic mass. Moreover, their position in the circular velocity--baryonic mass plane implies that they have a baryon fraction inside their virial radii compati…
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…
We study the gas kinematics traced by the 21-cm emission of a sample of six HI$-$rich low surface brightness galaxies classified as ultra-diffuse galaxies (UDGs). Using the 3D kinematic modelling code $\mathrm{^{3D}}$Barolo we derive robust circular velocities, revealing a startling feature: HI$-$rich UDGs are clear outliers from the baryonic Tully-Fisher relation, with circular velocities much lower than galaxies with similar baryonic mass. Notably, the baryon fraction of our UDG sample is consistent with the cosmological value: these UDGs are compatible with having no "missing baryons" withi…
Aims: It is well known that the presence of baryons affects the dark matter host haloes. Exploring the galaxy assembly history together with the dark matter haloes properties through time can provide a way to measure these effects. Methods: We study the properties of four Milky Way mass dark matter haloes from the Aquarius project during their assembly history, between $z = 0 - 4$. In this work, we use the SPH run from Scannapieco et al. (2009) and the dark matter only counterpart as case studies. To asses the robustness of our findings, we compare them with one of the haloes run using a movin…
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 revisit the question of 'hot mode' versus 'cold mode' accretion onto galaxies using steady-state cooling flow solutions and idealized 3D hydrodynamic simulations. We demonstrate that for the hot accretion mode to exist, the cooling time is required to be longer than the free-fall time near the radius where the gas is rotationally-supported, R_circ, i.e. the existence of the hot mode depends on physical conditions at the galaxy scale rather than on physical conditions at the halo scale. When allowing for the depletion of the halo baryon fraction relative to the cosmic mean, the longer coolin…
In $Λ$CDM cosmology, to first order, galaxies form out of the cooling of baryons within the virial radius of their dark matter halo. The fractions of mass and angular momentum retained in the baryonic and stellar components of disc galaxies put strong constraints on our understanding of galaxy formation. In this work, we derive the fraction of angular momentum retained in the stellar component of spirals, $f_j$, the global star formation efficiency $f_M$, and the ratio of the asymptotic circular velocity ($V_{\rm flat}$) to the virial velocity $f_V$, and their scatter, by fitting simultaneousl…
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 …
