年青恒星体喷流理论和观测

年青恒星体中喷流现象很普遍。大量天体物理文献瞄准了活动星系核、共生恒星、行星状星云和X射线双星中的物质喷发现象。在恒星形成中基本开放的问题之一是物理机制。物质从原恒星系统喷发，进入喷流。部分喷流控制系统角动力，并且在最初的几百万年里演化。在大尺度上，喷流为恒星形成和演化注入动力。     

A2142星系团子结构中的星系演化

系统整理了星系团A2142的光谱和测光数据．利用花树算法得到的子结构,将星系团视场中的星系分为非子结构、子结构和外围星系3类．通过研究它们的分布、产星活动、D_n4000等物理信息,发现了A2142星系团中的星系存在明显的径向演化趋势．星系从星系团外围落入团中心的过程中,其演化不仅受到星系团内介质的影响,还受到子结构自身的调制．      

星系喷流的一种可能能源机制:两个黑洞叠加时的Hawking辐射

提出星系喷流的一种可能能源机制:2个叠加黑洞的相交奇区可能存在热辐射,这种辐射足以提供星系喷流所需要的能量.论述了奇区产生辐射的可能性,计算了辐射功率,结果表明只要适当选择一些参量就可以解释星系喷流现象.     

M51星系盘上HCN J=1-0发射线的成图观测

为了解致密分子气体在星系盘上的分布,我们使用IRAM 30 m望远镜对M51的HCN J=1-0分子发射线进行了成图观测(角分辨率为28").成图区域达4'×5'(1'~2.9 kpc),是目前为止对M51 HCN J=1-0发射线进行的最为延展的一次成图观测.将之与NRO 45 m望远镜观测得到的CO J=1-0发射线数据进行比较,我们对M51星系内致密分子气体与总分子气体分布的差异与相关性等特性进行了讨论.HCN分布呈现出向星系中心集中的趋势,中心区域的HCN积分强度是星系盘上的3–4倍.在HCN积分强度图中也观测到了由CO发射所示踪的气体旋臂.M51总HCN光度是中心主波束区域(kpc尺度)的5倍,这说明了依然存在很多的致密分子气体分布在星系中心核区之外.在距星系光学中心42'内的区域(包含核球区的星系内盘),距离星系中心越远,HCN/CO的积分强度比越小;而在远离星系中心的星系盘上(大于42")该比值基本保持恒定.对于星系盘上的大部分区域,IHCN和ICO具有非常紧密的线性相关性,最小二乘法拟合的斜率为1.2.而对于核球区它们的拟合斜率则要高得多(2.3).所有这些都说明了致密分子气体的性质(例如含量、发射条件、HCN的丰度)在核球区和星系盘上是不一样的.     

星系周介质的研究方法和研究进展

星系周介质是位于星系维里半径以内、星际介质以外的气体.这些弥散的、几乎不可见的物质在星系的演化过程中扮演了重要的角色.本文介绍星系周介质的研究方法以及近年来取得的主要研究进展，包括重子物质的质量分布和金属分布等.研究表明，星系周介质是复杂的多相气体，不同温度的星系周介质都包含了大量的重子物质，有望解决标准宇宙学框架下的“重子物质缺失”问题.星系周介质的金属分布呈双峰或更复杂的结构，说明其能接收星系反馈过程抛出的气体，调节并支配星系的气体供给.观测上已经发现星系内流和外流的直接证据，星系周介质的性质具体是如何影响星系中气体的供给还有待研究.未来，包括我国的中国空间站望远镜、宇宙热重子探寻计划等观测设备将帮助人们更好地理解星系周介质的性质及其在星系演化过程中的具体作用.     

喷流内粒子同步加速辐射数值解研究

同步加速辐射是活动星系核低能辐射的主要辐射机制。研究喷流内粒子的同步加速辐射过程对认识活动星系核内部辐射机制,能谱分布、光变时标等热点问题非常重要。文章研究活动星系核喷流内粒子的同步辐射过程,用数值的方法得到喷流内粒子的同步辐射谱分布情况,用得到的粒子谱分布计算了BL Lac天体PKS 2155-304低能辐射。结果表明,PKS 2155-304低能辐射能用同步辐射很好地解释。     

星系团Abell 2199的动力学子结构

近年来Sloan巡天的光谱观测使近邻富星系团Abell 2199的成员星系数目增加了近两倍.基于该星系团1.5 h-1Mpc范围内的366颗成员星系的位置和红移信息,对其动力学结构进行了分析.计算出中心cD星系的本动速度为(189±45)kms-1,说明cD星系在星系团完全维力化之前就形成了.从这些星系的空间分布和局域视向速度分布中,发现了三个明显的子团.这些子团的并合现象表明,星系团Abell 2199远未达到动力学平衡状态,从而支持了星系团形成的等级模型     

Abell 2634中心区域成员星系的光度函数

我们得到了邻近星系团Abell 2634中心区域的198颗成员星系在B、V、R三个波段的光度函数，并且分别用Schechter函数和Gaussian函数及其组合进行了拟合．我们将所得到的光度函数与其它星系团的光度函数以及场星系的光度函数进行了比较，发现与Conma星系团的光度函数一致，而与场星系的光度函数存在较大的差异．我们认为这种差异可能是由星系团的环境因素引起的．     

Blandford_Znajek过程的相对重要性

给出了Blandford_Znajek（BZ）过程的喷流功率和来自于吸积盘内区喷流功率的解析表达式，并对两者的功率和力矩大小作了比较分析。结果表明当黑洞自转不特别大的情况下，来自于吸积盘内区的喷流功率明显大于来自于旋转黑洞的BZ功率     

首次成功观测黑洞“进食”

星系中心的大质量黑洞历来都是一个“贪得无厌”的家伙，但是天文学家却从未亲眼目睹它们大快朵牙颐时的样子。如今，天文望远镜终于向我们展示了动荡星系中心的一个“大吃大喝”的黑洞的景象——从最近距离观测到一个气态螺旋被黑洞吞噬的过程。     

A massive, cooling-flow-induced starburst in the core of a luminous cluster of galaxies

In the cores of some clusters of galaxies the hot intracluster plasma is dense enough that it should cool radiatively in the cluster's lifetime, leading to continuous 'cooling flows' of gas sinking towards the cluster centre, yet no such cooling flow has been observed. The low observed star-formation rates and cool gas masses for these 'cool-core' clusters suggest that much of the cooling must be offset by feedback to prevent the formation of a runaway cooling flow. Here we report X-ray, optical and infrared observations of the galaxy cluster SPT-CLJ2344-4243 (ref. 11) at redshift z = 0.596. These observations reveal an exceptionally luminous (8.2?×?10(45)?erg?s(-1)) galaxy cluster that hosts an extremely strong cooling flow (around 3,820 solar masses a year). Further, the central galaxy in this cluster appears to be experiencing a massive starburst (formation of around 740 solar masses a year), which suggests that the feedback source responsible for preventing runaway cooling in nearby cool-core clusters may not yet be fully established in SPT-CLJ2344-4243. This large star-formation rate implies that a significant fraction of the stars in the central galaxy of this cluster may form through accretion of the intracluster medium, rather than (as is currently thought) assembling entirely via mergers.     

Regulation of the X-ray luminosity of clusters of galaxies by cooling and supernova feedback.

Clusters of galaxies are thought to contain about ten times as much dark matter as baryonic matter. The dark component therefore dominates the gravitational potential of a cluster, and the baryons confined by this potential radiate X-rays with a luminosity that depends mainly on the gas density in the cluster's core. Predictions of the X-rays' properties based on models of cluster formation do not, however, agree with the observations. If the models ignore the condensation of cooling gas into stars and feedback from the associated supernovae, they overestimate the X-ray luminosity because the density of the core gas is too high. An early episode of uniformly distributed supernova feedback could rectify this by heating the uncondensed gas and therefore making it harder to compress into the core, but such a process seems to require an implausibly large number of supernovae. Here we show how radiative cooling of intergalactic gas and subsequent supernova heating conspire to eliminate highly compressible low-entropy gas from the intracluster medium. This brings the core entropy and X-ray luminosities of clusters into agreement with the observations, in a way that depends little on the efficiency of supernova heating in the early Universe.     

A large population of 'Lyman-break' galaxies in a protocluster at redshift z approximately 4.1

The most massive galaxies and the richest clusters are believed to have emerged from regions with the largest enhancements of mass density relative to the surrounding space. Distant radio galaxies may pinpoint the locations of the ancestors of rich clusters, because they are massive systems associated with 'overdensities' of galaxies that are bright in the Lyman-alpha line of hydrogen. A powerful technique for detecting high-redshift galaxies is to search for the characteristic 'Lyman break' feature in the galaxy colour, at wavelengths just shortwards of Lyalpha, which is due to absorption of radiation from the galaxy by the intervening intergalactic medium. Here we report multicolour imaging of the most distant candidate protocluster, TN J1338-1942 at a redshift z approximately 4.1. We find a large number of objects with the characteristic colours of galaxies at that redshift, and we show that this excess is concentrated around the targeted dominant radio galaxy. Our data therefore indicate that TN J1338-1942 is indeed the most distant cluster progenitor of a rich local cluster, and that galaxy clusters began forming when the Universe was only ten per cent of its present age.     

The heating of gas in a galaxy cluster by X-ray cavities and large-scale shock fronts

Most of the baryons in galaxy clusters reside between the galaxies in a hot, tenuous gas. The densest gas in their centres should cool and accrete onto giant central galaxies at rates of 10-1,000 solar masses per year. No viable repository for this gas, such as clouds or new stars, has been found. New X-ray observations, however, have revealed far less cooling below X-ray temperatures than expected, altering the previously accepted picture of cooling flows. As a result, most of the gas must be heated to and maintained at temperatures above approximately 2 keV (ref. 3). The most promising heating mechanism is powerful radio jets emanating from supermassive black holes in the central galaxies of clusters. Here we report the discovery of giant cavities and shock fronts in a distant (z = 0.22) cluster caused by an interaction between a radio source and the hot gas surrounding it. The energy involved is approximately 6 x 10(61) erg, the most powerful radio outburst known. This is enough energy to quench a cooling flow for several Gyr, and to provide approximately 1/3 keV per particle of heat to the surrounding cluster.     

并合星系团MACS J0358.8-2955再分析

尝试用最新的方法重新分析并合星系团MACS J0358.8-2955，给出并合事件的更多细节:在光学波段，采用花树算法寻找星系团子结构，确认了2个子结构的存在，并给出了具体成员；在X 射线波段，通过X射线光谱拟合，得到星系团内介质的红移分布，既给出了X射线气体与光学星系关联的直接证据，也呈现出2个子团的接近路径；ClusterPyXT工具生成的高分辨率温度图还揭示了周围环境中的激波加热信号，给出了并合成分的运动轨迹．新方法提供的光学星系和热气体的视向速度运动信息，较好地补充了星系团MACSJ0358并合过程的已有认识，构建出一个完整的并合早期三维图景．      

Suppression of star formation in early-type galaxies by feedback from supermassive black holes

Detailed high-resolution observations of the innermost regions of nearby galaxies have revealed the presence of supermassive black holes. These black holes may interact with their host galaxies by means of 'feedback' in the form of energy and material jets; this feedback affects the evolution of the host and gives rise to observed relations between the black hole and the host. Here we report observations of the ultraviolet emissions of massive early-type galaxies. We derive an empirical relation for a critical black-hole mass (as a function of velocity dispersion) above which the outflows from these black holes suppress star formation in their hosts by heating and expelling all available cold gas. Supermassive black holes are negligible in mass compared to their hosts but nevertheless seem to play a critical role in the star formation history of galaxies.     

团星系和场星系的恒星形成性质

通过对团星系和场星系的聚度参数、特征恒星形成率、星系中包含的恒星质量、金属丰度等物理参量的比较,研究了处在不同引力环境中星系的恒星形成性质.研究表明,聚度高的星系主要居于星系团中,大部分低质量星系是场星系,星系的特征恒星形成率与恒星质量和金属丰度之间存在着显著的相关.另外,团星系和场星系在红移小于0.1的范围内仍表现出了明显的宇宙学演化效应.     

A massive protocluster of galaxies at a redshift of z ≈ 5.3

Massive clusters of galaxies have been found that date from as early as 3.9 billion years (3.9 Gyr; z = 1.62) after the Big Bang, containing stars that formed at even earlier epochs. Cosmological simulations using the current cold dark matter model predict that these systems should descend from 'protoclusters'-early overdensities of massive galaxies that merge hierarchically to form a cluster. These protocluster regions themselves are built up hierarchically and so are expected to contain extremely massive galaxies that can be observed as luminous quasars and starbursts. Observational evidence for this picture, however, is sparse because high-redshift protoclusters are rare and difficult to observe. Here we report a protocluster region that dates from 1 Gyr (z = 5.3) after the Big Bang. This cluster of massive galaxies extends over more than 13 megaparsecs and contains a luminous quasar as well as a system rich in molecular gas. These massive galaxies place a lower limit of more than 4 × 10(11) solar masses of dark and luminous matter in this region, consistent with that expected from cosmological simulations for the earliest galaxy clusters.     

多股受限撞击射流井底压力特征的数值模拟

应用大涡模拟方法，对不同的喷嘴尺寸、个数和喷嘴组合条件下井底多股受限撞击射流的流动特性进行了数值模拟．对模拟结果的分析研究表明，多股撞击射流的井底压力分布存在低压区、高压区和中等压力区三个区域．高压区为射流撞击区，低压区为漫流区，中等压力区为射流相互干扰区．在喷嘴出口总面积相同的条件下，保持中心喷嘴直径大于或等于边喷嘴直径，井底压力的分布对清岩和破岩更为有利