Context. Stellar migration of the galactic disc stars has been invoked to explain the dispersion of stellar metallicity observed in the solar neighborhood. Aims. We seek to identify the dynamical mechanisms underlying stellar migration in an isolated galaxy disc under the influence of a bar. Our approach is to analyze the diffusion of dynamical quantities. Methods. We extend our previous work by exploring Chirikov's diffusion rate (and derived timescale) of the radial action $J_\mathrm{R}$ in an idealised N$-$body simulation of an isolated disc galaxy. We limit our study to the evolution of the disc region well after the formation of the bar, in a regime of adiabatic evolution. Results. The $J_\mathrm{R}$ diffusion timescales $T_\mathrm{D}(J_\mathrm{R})$ is less than 3 Gyr for roughly half the galaxy mass. It is always much shorter than the angular momentum diffusion timescale $T_\mathrm{D}(L_\mathrm{z})$ outside the stellar bar. In the disc, $\langle T_\mathrm{D}(J_\mathrm{R}) \rangle \sim 1$ Gyr. All non-axisymmetric morphological structures characteristic of resonances and waves in the disc are associated to particles with $T_\mathrm{D}(J_\mathrm{R}) < 3$ Gyr and $T_\mathrm{D}(L_\mathrm{z}) > 10$ Gyr. Short $T_\mathrm{D}(J_\mathrm{R})$ can be explained by the gradual decircularisation of initially circular orbits ($J_\mathrm{R}=0$) under the effect of intermittent ILR scattering by wave trains propagating in the disc, well beyond the bar OLR. This leads to a moderate secular heating of the disc beyond the bar OLR for 7 Gyr, comparable to solar neighbourhood observations. The complex multi-wave structure, mixing permanent and intermittent modes, allows for multiple resonance overlaps.
Galactic r-process abundance feature shaped by radial migration
以[Eu/Fe] vs. [Fe/H]图为代表的邻近盘星中r-过程元素的化学特征引起了人们越来越多的兴趣,因为它可以通过与理论模型的比较来评估r-过程元素的起源,包括检验中子星合并是否可以成为r-过程核合成的主要场所。另一方面,最近的研究表明,本地化学是强烈耦合的动力学的银河系盘,这预示着恒星径向移动的磁盘上观察到的元素特征是不同的,在不同的银心距离。在这里,我们表明,径向迁移的恒星在银河系盘在塑造太阳附近的r-过程丰度功能起着至关重要的作用。在这个方案中,我们强调了从外盘迁移的重要性,其中一些老恒星的[r-过程/Fe]被预测将增强到超出预期的水平,从观测到的银河系Fe和Eu径向梯度,这导致在附近的盘星之间的[r-过程/Fe]的大跨度。在[r-过程/铁]比率的变化,看到整个银河系盘以及矮星系可能是不同的恒星初始质量函数的结果,改变超新星之间的发生频率留下中子星和那些结束与黑洞。在这里,我们提出,增强[Eu/Fe]是由于初始质量函数缺乏高质量的恒星,如> 25太阳质量的方案,其中中子星合并是一个主要来源的r-过程元素。
Homogeneous metallicities and radial velocities for Galactic globular clusters. II. New CaT metallicities for 28 distant and reddened globular clusters
Up-to-date data on 2214 classical Cepheids have been used. The model of an exponential matter density distribution in the Galactic thin disk has been applied. New estimates of the radial disk scale length $h_R,$ the distance of the Sun from the symmetry plane $z_\odot$, and the vertical disk scale height $h_z$ have been obtained. Based on samples of 1087 Cepheids younger than 120 Myr and 1127 Cepheids older than 120 Myr, we have found $h_R=2.30\pm0.09$ kpc and $h_R=1.96\pm0.12$ kpc, respectively. It has turned out that an unambiguous estimate of $h_R$ cannot be obtained from their overall radi…
As heating processes can broaden the distributions of radial actions and the vertical distributions of the Galactic disks, we investigate the vertical distribution of the Galactic disks as a function of radial action based on Apache Point Observatory Galactic Evolution Experiment(APOGEE) and Gaia data in order to deepen our understanding of the formation and heating history of the Galactic disks. We find that the distributions of radial action for both the thin and thick disks can be approximately described by pseudo-isothermal distributions, which give a statistical measurement for the temper…
The chemical evolution of local star forming galaxies: Radial profiles of ISM metallicity, gas mass, and stellar mass and constraints on galactic accretion and winds
本文利用一个假定星系风质量损失和吸积质量增加与恒星形成速率之比为常数的分析化学演化模型,研究了20个盘状星系的ISM和年轻恒星星族的径向平均金属丰度分布。基于这个模型,观测到的金属丰度及其梯度可以用恒星质量与ISM气体质量之比的径向平均分布来描述。观测到的和模型预测的金属丰度之间的比较被用来约束质量损失率通过星系风和吸积增益单位的恒星形成率。发现了三组星系:要么大部分是风,只有微弱的吸积,要么大部分是吸积,只有微弱的风,和星系的风大致平衡的吸积。这三组气体盘的性质是不同的。质量损失率和吸积增益率近似相等的星系具有低金属丰度,原子氢占主导地位的气体盘具有平坦的空间轮廓。另外两组的气体盘由分子氢主导,等照度半径为0.5至0.7,并显示出径向指数下降,这是平均陡峭的星系与小吸积率。吸积率(<1.0 x SFR)和外流率(<2.4 x SFR)相对较低。后者依赖于使用HII区强发射线对金属丰度测定的零点进行校准。
We present a table of 215 SNRs with distances. New distances are found to SNR G$51.26+0.11$ of $6.6 \pm 1.7$ kpc using HI absorption spectra, and to 5 other SNRs using maser/molecular cloud associations. We recalculate the distances and errors to all SNRs using a consistent rotation curve and provide errors where they were not previously estimated. This results in a significant distance revisions for 20 SNRs. Because of observational constraints and selection effects, there to be is an apparent deficit of observed number of Galactic supernova remnants (SNRs). To investigate this, we employ two…
Galactic Large-scale Filaments Resident in Asymmetric Environments: Clues from Cross-filament Profiles of Density and Temperature
Kavli Institute for Astronomy and Astrophysics, Peking University(北京大学科维理天文与天体物理研究所);Department of Astronomy, School of Physics, Peking University(北京大学物理学院天文学系);Max Planck Institute for Astronomy(马克斯·普朗克天文学研究所)
We present optical spectra of nine Galactic H II regions observed with the 10.4 m Gran Telescopio Canarias telescope and located at Galactocentric distances (RG) from 4 to 8 kpc. The distances of the objects have been revised using Gaia DR2 parallaxes. We determine the electron temperature for all the nebulae, which allows a precise computation of their ionic abundances. We have included published data of an additional sample of Galactic H II regions, providing a final data set of 42 objects. The shape of the radial gradients of O/H and N/H is linear and constant, discarding any substantial ch…
Due to its proximity, the stellar populations of the Galactic bulge (GB) can be resolved and can be studied in detail. This allows tracing the bulge metallicity distribution function (MDF) for different spatial regions within the bulge, which may give us clues about the bulge formation and evolution scenarios. In this work, we developed a chemical evolution model (CEM), taking into account the mass distribution in the bulge and disc, to derive the radial dependence of this time-scale in the Galaxy. Since the infall rate depends on that time scale in the CEM, the results of the model were used …
The contact frontier in Galactic civilization networks: radial structure and the Galactic habitable zone
Frontier Research Institute for Interdisciplinary Science, Tohoku University(东北大学前沿跨学科研究院);Department of Natural Science, Faculty of Science and Engineering, Tokyo City University(东京都立科学大学理工学部自然科学系)
Supernovae are the dominant source of chemical enrichment of galaxies, and they are an important source of energy to heat the interstellar medium and accelerate cosmic rays. Our knowledge of supernovae in the Milky Way is based mostly on the study of Galactic supernova remnants (SNRs), providing an (incomplete) record to supernova activity over the last ~100,000 yr. Here we report on an investigation of the spatial distribution of Galactic SNRs. Given the limited number of SNRs it is common to assume a functional form for the Galactocentric distribution of SNRs. However, several functional for…
Evidence of radial-migration driven Galactic disc expansion with the U-shape stellar age profile
South-Western Institute for Astronomy Research, Yunnan University(西南天文研究所,云南大学);Yunnan Key Laboratory of Survey Science, Yunnan University(云南省测绘科学重点实验室,云南大学)