重子物质对暗物质晕形状和角动量的影响          下载免费PDF全文

张瑶瑶  戴才萍 《天文学报》2021,62(6):65

利用高精度大样本的冷暗物质($\Lambda$ cold dark matter, $\Lambda$CDM)宇宙学数值模拟的数据, 对重子物质如何影响暗物质晕的形状和角动量进行了研究.使用了3种数值模拟数据, 纯暗物质模拟、含辐射冷却、恒星形成和动力学超新星反馈的模拟, 包含活动星系核反馈效应的恒星形成模拟. 对这3种模拟, 还进行了不同红移处的比较. 主要结果如下.重子物理过程会改变暗物质晕的质量分布, 特别是有活动星系核反馈机制的情况下.比如, 活动星系核反馈会减少大质量暗物质晕的形成.随着宇宙的演化, 暗物质晕的空间形态逐渐由扁变圆. 重子物质的存在会加速暗物质晕形状的变化过程, 而且会使暗物质晕形状变得更圆. 但是活动星系核的反馈会对这一加速效应产生抑制.重子物质对暗物质晕的影响与暗物质晕的质量和半径都存在一定的依赖性.暗物质晕的质量越大, 它会呈现更扁的形态. 同时, 重子物质对任意质量的暗物质晕或暗物质晕在任意半径处的变圆均有一定的促进作用,尽管活动星系核反馈会抑制这一促进作用.特别是对于暗物质晕在0.2--0.6倍维里半径处的形状, 重子物质的影响尤为明显.此外, 重子物质的存在会对暗物质晕的角动量产生显著影响, 它会增大暗物质的角动量. 暗物质晕的自旋参数与质量无相关性, 但是与暗物质晕的半径存在一定的相关性.  相似文献   

泥岩成岩作用研究进展与展望     

赵建华  金之钧 《沉积学报》2021,39(1):58-72

泥岩成岩作用研究在页岩油气革命的推动下取得了一系列重要进展,已成为沉积学和石油地质学研究的一个前缘领域.泥岩成岩作用不仅控制着油气的生成和运移,同时对物质组成、微观结构、储层物性和力学性质都具有重要影响.本文围绕这一领域,阐述了国内外相关研究现状,展望了未来的发展趋势.当前泥岩成岩作用研究进展主要体现在4个方面:1)矿...  相似文献   

宇宙大尺度结构空洞的演化研究     

赵飞  罗煜  韦成亮 《天文学报》2019,60(4):87-102

为了研究空洞的演化以及暗物质空洞和星系空洞的差别,使用一组高精度的N体模拟数据以及基于此给出的半解析模拟星系数据,在红移2.03到红移0之间取了6个红移的数据,并使用VIDE (Void Identification and Examination toolkit)算法来找空洞,对星系空洞和暗物质空洞的统计性质比如丰度、数目、大小、形状、叠加密度轮廓等演化的比较的结果表明,随着红移的减小,空洞的数目逐渐减少、内部密度逐渐变小、体积逐渐增大、空洞的形状越来越扁.暗物质空洞和星系空洞的数目、平均大小、平均椭率的比值与红移呈线性关系.此外,不论是暗物质空洞还是星系空洞,小的空洞密度比在分布上比大空洞的低,更容易贯通并合,演化效应更明显.另外由于星系总是形成于暗物质密度场的高密度区域,使其不容易示踪暗物质空洞的一些薄弱的墙结构,导致星系空洞提前贯通.而对于已经形成的星系空洞而言,即便是其墙上最薄弱的地方也往往堆积着显著的暗物质,使得星系的位置保持稳定,甚至形成新的星系,从而抑制星系空洞的贯通.整体上暗物质空洞的演化要比星系空洞的演化更加明显.  相似文献   

Probing dark matter,galaxies and the expansion history of the Universe with Lyα in absorption and emission     

M.G. Haehnelt 《Astronomische Nachrichten》2010,331(5):541-548

Lyα radiation is an important diagnostic tool in a wide range of astrophysical environments. I will first describe here how measurements of the matter power spectrum on small scales from Lyα forest data constrain the mass of dark matter particles. I then will report on an ambitious program of searching for very faint spatially extended Lyα emission at z ∼ 3 which has led to the discovery of a new population of faint Lyα emitters which I will argue should be identified with the long searched for host galaxies of damped Lyα absorbers. Finally, I will discuss the possibility of measuring the redshift drift of Lyα absorption features and therefore the change of the expansion rate of the Universe in real time with the ultra‐stable high‐resolution spectrograph CODEX proposed for the E‐ELT (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Tidal tails of star clusters     

Andreas H. W. Küpper  Pavel Kroupa  Holger Baumgardt  Douglas C. Heggie 《Monthly notices of the Royal Astronomical Society》2010,401(1):105-120

Based on recent findings of a formation mechanism of substructure in tidal tails by Küpper et al., we investigate a more comprehensive set of N -body models of star clusters on orbits about a Milky Way like potential. We find that the predicted epicyclic overdensities arise in any tidal tail no matter which orbit the cluster follows as long as the cluster lives long enough for the overdensities to build up.
The distance of the overdensities along the tidal tail from the cluster centre depends for circular orbits only on the mass of the cluster and the strength of the tidal field, and therefore decreases monotonically with time, while for eccentric orbits the orbital motion influences the distance, causing a periodic compression and stretching of the tails and making the distance oscillate with time. We provide an approximation for estimating the distance of the overdensities in this case.
We describe an additional type of overdensity which arises in extended tidal tails of clusters on eccentric orbits, when the acceleration of the tidal field on the stellar stream is no longer homogeneous. Moreover, we conclude that a pericentre passage or a disc shock is not the direct origin of an overdensity within a tidal tail. Escape due to such tidal perturbations does not take place immediately after the perturbation but is rather delayed and spread over the orbit of the cluster. All observable overdensities are therefore of the mentioned two types. In particular, we note that substructured tidal tails do not imply the existence of dark matter substructures in the haloes of galaxies.  相似文献   

Constrained simulations of the local universe – II. The nature of the local Hubble flow     

Luis A. Martinez-Vaquero  Gustavo Yepes  Yehuda Hoffman  Stefan Gottlöber  Mira Sivan 《Monthly notices of the Royal Astronomical Society》2009,397(4):2070-2080

Using a suite of N -body simulations in different cold dark matter (CDM) scenarios, with cosmological constant (ΛCDM) and without (OCDM, SCDM), we study the Hubble flow (σ_H) in Local Volumes (LV) around Local Group (LG) like objects found in these simulations, and compare the numerical results with the most recent observations. We show that ΛCDM and OCDM models exhibit the same behaviour of σ_H. Hence, we demonstrate that the observed coldness of the Hubble flow is not likely to be a manifestation of the dark energy, contrary to previous claims. The coldness does not constitute a problem by itself but it poses a problem to the standard ΛCDM model only if the mean density within the LV is greater than twice the mean matter cosmic density. The lack of blueshifted galaxies in the LV, outside of the LG can be considered as another manifestation of the coldness of the flow. Finally, we show that the main dynamical parameter that affects the coldness of the flow is the relative isolation of the LG, and the absence of nearby Milky Way like objects within a distance of about  3 Mpc  .  相似文献   

Stellar velocity profiles and line strengths out to four effective radii in the early-type galaxies NGC 3379 and 821     

Anne-Marie Weijmans  Michele Cappellari  Roland Bacon  P. T. de Zeeuw  Eric Emsellem  Jesús Falcón-Barroso  Harald Kuntschner  Richard M. McDermid  Remco C. E. van den Bosch  Glenn van de Ven † 《Monthly notices of the Royal Astronomical Society》2009,398(2):561-574

We use the integral-field spectrograph SAURON to measure the stellar line-of-sight velocity distribution and absorption line strengths out to four effective radii ( R _e) in the early-type galaxies NGC 3379 and 821. With our newly developed observing technique, we can now probe these faint regions in galaxies that were previously not accessible with traditional long-slit spectroscopy. We make optimal use of the large field-of-view and high throughput of the spectrograph: by adding the signal of all ∼1400 lenslets into one spectrum, we obtain sufficient signal-to-noise in a few hours of observing time to reliably measure the absorption line kinematics and line strengths out to large radius.
We find that the line strength gradients previously observed within 1 R _e remain constant out to at least 4 R _e, which puts constraints on the merger histories of these galaxies. The stellar halo populations are old and metal poor. By constructing orbit-based Schwarzschild dynamical models, we find that dark matter is necessary to explain the observed kinematics in NGC 3379 and 821, with 30–50 per cent of the total matter being dark within 4 R _e. The radial anisotropy in our best-fitting halo models is less than in our models without halo, due to differences in orbital structure. The halo also has an effect on the  Mg  b – V _esc  relation: its slope is steeper when a dark matter halo is added to the model.  相似文献   

Galaxy clustering and galaxy–galaxy lensing: a promising union to constrain cosmological parameters     

Marcello Cacciato †  Frank C. van den Bosch  Surhud More  Ran Li  H. J. Mo  Xiaohu Yang 《Monthly notices of the Royal Astronomical Society》2009,394(2):929-946

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Cosmology with the cluster mass function: mass estimators and shape systematics in large weak lensing surveys     

Virginia L. Corless  Lindsay J. King 《Monthly notices of the Royal Astronomical Society》2009,396(1):315-324

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Dark stars at the Galactic Centre – the main sequence     

Pat Scott  Malcolm Fairbairn  Joakim Edsjö 《Monthly notices of the Royal Astronomical Society》2009,394(1):82-104

In regions of very high dark matter density such as the Galactic Centre, the capture and annihilation of WIMP dark matter by stars has the potential to significantly alter their evolution. We describe the dark stellar evolution code D ark S tars , and present a series of detailed grids of WIMP-influenced stellar models for main-sequence stars. We describe the changes in stellar structure and main-sequence evolution which occur as a function of the rate of energy injection by WIMPs, for masses of  0.3–2.0 M_⊙  and metallicities   Z = 0.0003–0.02  . We show what rates of energy injection can be obtained using realistic orbital parameters for stars at the Galactic Centre, including detailed consideration of the velocity and density profiles of dark matter. Capture and annihilation rates are strongly boosted when stars follow elliptical rather than circular orbits. If there is a spike of dark matter induced by the supermassive black hole at the Galactic Centre, single solar mass stars following orbits with periods as long as 50 yr and eccentricities as low as 0.9 could be significantly affected. Binary systems with similar periods about the Galactic Centre could be affected on even less eccentric orbits. The most striking observational effect of this scenario would be the existence of a binary consisting of a low-mass protostar and a higher mass evolved star. The observation of low-mass stars and/or binaries on such orbits would either provide a detection of WIMP dark matter, or place stringent limits on the combination of the WIMP mass, spin-dependent nuclear-scattering cross-section, halo density and velocity distribution near the Galactic Centre. In some cases, the derived limits on the WIMP mass and spin-dependent nuclear-scattering cross-section would be of comparable sensitivity to current direct-detection experiments.  相似文献