塞弗特2型星系窄线区的形态

使用国家天台兴隆观测站2．16m望远镜的BFOSC相机，对6个塞弗特2型星系进行了窄带成像观测，并获得了它们的[OⅢ]λ007和Ha [NⅡ]λλ6548，6583发射线像以及邻近的连续辐射像，用来研究其窄线区延展电离气体的形态和性质．根据简化的活动星系核的统一模型，假设窄线区气体成球状分布，那么应观测到塞弗特2型星系的窄线区电离气体成V-状(电离锥)．但观测表明，只在一些塞弗特2型星系中观测到了电离锥，而在另外一些塞弗特2型星系中观测到了简化的活动星系核统一模型所不能解释的窄线区电离气体的“晕”状形态．结合观测结果，讨论了导致在塞弗特星系中观测到窄线区电离锥和其它不同形态的因素以及对活动星系核统一模型的验证等相关问题．     

1RXP J160338+1554.1:一个明亮的低电离核发射线区星系

X射线卫星ROSAT观测得到的X射线源1RXP J160338+1554.1,经过美国基特峰国立天文台的4 m光学望远镜的分光观测得到了它的光谱.通过光谱分析发现,该源具有较强的低电离发射线,从发射线的强度比以及谱线形态来看,该源完全符合低电离核发射线区(LINERs)星系的判据.这是第一次完全证实它是一个LINER.     

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.     

远红外亮类星体的研究进展

远红外亮类星体是极亮红外星系中具有I型活动星系核光谱特征的天体,光学光谱研究表明它们在光学波段的辐射主要由中心活动星系核主导,其中心超大质量黑洞的质量为107~108M☉,且有超爱丁顿吸积率.与光学选类星体相比,远红外亮类星体在远红外波段存在明显的辐射超出,这可能是由其核区周围~1 kpc尺度内的星暴活动(恒星形成率约为几百M☉yr-1)加热尘埃造成.对分子气体进行观测发现远红外亮类星体的宿主星系中存在约109~1010M☉的分子气体,这些分子气体可以为黑洞和核球的增长提供"原料".几乎所有远红外亮类星体都处于富气星系并合的晚期,是极亮红外星系向光学选类星体演化的过渡天体.     

多姿多彩的神秘星空——近期发生的重要天象介绍(2)

南风车星系——M83M83是离我们最近和最明亮的旋涡星系之一。它位于长蛇座,用双筒望远镜就能看到。因为它具有壮丽的旋臂,因此 M83赢得"南风车星系"的雅号。远在250年前,天文学家就已经发现了 M83。不过直到本世纪初,天文学家才弄清楚 M83和我们的银河系很像,是个棒旋星系,而不是一团雾蒙蒙的云气。这张 M83的照片,是欧洲南方天文台用甚大望远镜(VLT)拍摄,并于最近刚公布的影像。M83是它所在星系团中很显眼的成员,这个星系团的成员包括半人马座 A 和 NGC 5253,这些星系和我们之间的距离约有1500万光年。到现在为止,天文学家已经在 MB3找到6颗超新星。最近天文学家又在 M83的核心区,发现了一个双层的拱核环,但     

科学家发现已知距地球最远小型黑洞

日前，德国马克斯·普朗克天文研究所发表公报说，欧洲南方天文台的专家发现，在距离地球约600万光年、代号为NGC300的螺旋星系中有一个小型黑洞．这个黑洞的质量约为太阳的15倍，是迄今发现的第二大小型黑洞。研究人员介绍说，欧洲航天局首先通过XMM牛顿天文望远镜发现了这个NGC300星系中最强的辐射源，当时还未确认它为黑洞。     

活动星系核在光学波段的光度及光谱斜率变化

利用盘不稳定模型和星爆模型,模拟活动星系核在光学B、V波段的光变,分析光变时光谱斜率的变化情况,并将模拟的结果和观测进行比较,结果表明,这两种模型是定性解释活动星系核光学波段光度、光谱变化的合理模型．     

中红外选活动星系核中水脉泽辐射的搜寻

之前的研究显示水超脉泽辐射更倾向位于被物质严重遮掩的活动星系核中,因此,作者选择了一个活动星系核样本,开展水超脉泽的搜寻工作.该样本主要基于它们的中红外辐射特性(谱和颜色特性)而被证认为活动星系核,并由于被严重遮掩而未能在之前的光学观测中被证认.作者申请并获准应用德国Effelsberg 100 m口径望远镜,于2014年1月开展了水超脉泽的搜寻工作.观测结果显示只有几个源的谱存在可能的脉泽辐射,根据观测结果的噪声水平和这些星系的距离,作者估算了每个源的水脉泽辐射光度的上限值,这将对以后更高灵敏度的搜寻工作提供指导.     

中红外选活动星系核中水脉泽辐射的搜寻（英文）

之前的研究显示水超脉泽辐射更倾向位于被物质严重遮掩的活动星系核中,因此,作者选择了一个活动星系核样本,开展水超脉泽的搜寻工作.该样本主要基于它们的中红外辐射特性(谱和颜色特性)而被证认为活动星系核,并由于被严重遮掩而未能在之前的光学观测中被证认.作者申请并获准应用德国Effelsberg 100 m口径望远镜,于2014年1月开展了水超脉泽的搜寻工作.观测结果显示只有几个源的谱存在可能的脉泽辐射,根据观测结果的噪声水平和这些星系的距离,作者估算了每个源的水脉泽辐射光度的上限值,这将对以后更高灵敏度的搜寻工作提供指导.     

绚丽的气体星云

除了行星状星云外(见本刊今年第4期),天空中还存在着另外两种气体星云——电离氢区和超新星遗迹。顾名思义,电离氢区是指在该区域内的氢原子被电离了。当电离的氢原子与电子结合后就会发射氢线,在可见区就显现出巴尔末线系。几乎所有的气体星云都处在这种状态。但在天文上,电离氢区常常是特指与年轻恒星成协的气体星云。一团处于星际空间的分子云,包含气体和尘埃成份。当受到某种作用力,如磁场或微波的作用时,它就会形成一个凝聚核。这一凝聚核就变成了引力中心,使分子云进一步收缩。在收缩的过程中,下落的物质的势能变为动能,所以核区的温…     

A tidally distorted dwarf galaxy near NGC 4449

NGC 4449 is a nearby Magellanic irregular starburst galaxy with a B-band absolute magnitude of -18 and a prominent, massive, intermediate-age nucleus at a distance from Earth of 3.8?megaparsecs (ref. 3). It is wreathed in an extraordinary neutral hydrogen (H?I) complex, which includes rings, shells and a counter-rotating core, spanning ～90?kiloparsecs (kpc; refs 1, 4). NGC 4449 is relatively isolated, although an interaction with its nearest known companion--the galaxy DDO 125, some 40?kpc to the south--has been proposed as being responsible for the complexity of its H?I structure. Here we report the presence of a dwarf galaxy companion to NGC 4449, namely NGC 4449B. This companion has a V-band absolute magnitude of -13.4 and a half-light radius of 2.7?kpc, with a full extent of around 8?kpc. It is in a transient stage of tidal disruption, similar to that of the Sagittarius dwarf near the Milky Way. NGC 4449B exhibits a striking S-shaped morphology that has been predicted for disrupting galaxies but has hitherto been seen only in a dissolving globular cluster. We also detect an additional arc or disk ripple embedded in a two-component stellar halo, including a component extending twice as far as previously known, to about 20?kpc from the galaxy's centre.     

对NGC5128星系50 kpc内表面亮度轮廓的研究

NGC5128是距离地球最近的、可通过地面望远镜直接分辨其中红巨星分支恒星的巨椭球星系。通过分辨并计数该星系外晕中的红巨星分支恒星, 研究其星系晕的表面亮度轮廓, 并对位于该星系外恒星晕主轴方向的内外两个视场的图像进行测光研究, 这些CCD图像来自Magellan/IMACS f/4望远镜的V和I两个波段。通过星等和颜色对红巨星分支恒星进行筛选, 最终在两个视场的图像中分别得到包含4719和980个红巨星分支恒星候选的样本, 并将外场样本用于对内场污染的估计和矫正。采用 Sersic定律对内场表面亮度轮廓进行拟合, 得到的最佳拟合参数为: V波段, r_e = 6.21角分, μ_e = 22.05 mag/arcsec², n = 1.90, 拟合误差为0.37星等; I波段, r_e = 6.57角分, μ_e =20.79 mag/arcsec², n = 1.90, 拟合误差为0.41星等。结果显示V和I波段的拟合结果一致, 并且在数据的精度内, 没有发现轮廓向晕族突变的迹象。     

超新星1993J的观测

1993年3月26日西班牙一位天文爱好者F.Garcia用25cm的望远镜在M81(NGC3031)的星系核的西南方向5′处发现了超新星,ST-4的CCD成像系统也记录到这一颗超新星,IAU命名为SN1993J.M81位于大熊座,是旋涡星系(Sb),其距离模数m-M=27.5,即距离d=9.46×10~(19)km.它与M82和NGC3077构成三重星系群.SN1993J是在该星系观测到的第一颗超新星.它是继SN1987A之后观测到最亮的一颗超新星,坐标为:α=9~h51~m19~s.27,δ=69°15′25″7.     

A quasar possibly ejected from NGC4579

With the 2.16 m telescope at Beijing Astronomical Observatory, it is identified that a compact X-ray source detected by ROSAT located in the vicinity of 5′.9 from the LINER galaxy NGC4579 is a quasar with a redshift z = 0.106. A further analysis indicates that this quasar is possibly ejected from NGC4579.     

Molecular hydrogen beyond the optical edge of an isolated spiral galaxy

Knowledge about the outermost portions of galaxies is limited owing to the small amount of light coming from them. It is known that in many cases atomic hydrogen (H I) extends well beyond the optical radius. In the centres of galaxies, however, molecular hydrogen (H2) usually dominates by a large factor, raising the question of whether H2 is also abundant in the outer regions. Here we report the detection of emission from carbon monoxide (CO), the most abundant tracer of H2, beyond the optical radius of the nearby galaxy NGC 4414. The host molecular clouds probably formed in the regions of relatively high H i column density and in the absence of spiral density waves. The relative strength of the lines from the two lowest rotational levels indicates that both the temperature and density of the H2 are quite low compared to conditions closer to the centre. The inferred surface density of the molecular material continues the monotonic decrease from the inner regions. We conclude that although molecular clouds can form in the outer region of this galaxy, there is little mass associated with them.     

中等年龄疏散星团NGC752中的QXAnd变星的测光研究

QxAnd变星是中等年龄疏散星团NGC752中的一个短周期的WUMa类型的相接双星．在2007年9月10日到12月25日期间,利用国家天文台兴隆85cm反射式望远镜对QXAnd变星进行B和V测光研究．我们得到了B和V两个波段的光变曲线;利用K—W方法定出光变极小时刻;通过经典的O—C方法得到QXAnd变星的周期P=4．12168117d和周期变化率dp／dt=1．89×10^-7d／a．     

求解CCD图像几何扭曲的初步结果

准确求解望远镜成像系统中视场的几何扭曲是高精度天体测量中的关键环节.借鉴哈勃空间望远镜几何扭曲求解的思想,提出并实施了一种简便、有效的方法.应用到云南天文台1米望远镜2011年4月2～3日观测疏散星团M67所得的72幅CCD图像表明：望远镜存在明显的几何扭曲效应,在视场角落最大扭曲～0.6pixel（～120mas）.经扭曲改正后,视场中星象的定位精度有了明显提高.     

Magnetic support of the optical emission line filaments in NGC 1275

The giant elliptical galaxy NGC 1275, at the centre of the Perseus cluster, is surrounded by a well-known giant nebulosity of emission-line filaments, which are plausibly in excess of 10(8) years old. The filaments are dragged out from the centre of the galaxy by radio-emitting 'bubbles' rising buoyantly in the hot intracluster gas, before later falling back. They act as markers of the feedback process by which energy is transferred from the central massive black hole to the surrounding gas. The mechanism by which the filaments are stabilized against tidal shear and dissipation into the surrounding extremely hot (4 x 10(7) K) gas has been unclear. Here we report observations that resolve thread-like structures in the filaments. Some threads extend over 6 kpc, yet are only 70 pc wide. We conclude that magnetic fields in the threads, in pressure balance with the surrounding gas, stabilize the filaments, so allowing a large mass of cold gas to accumulate and delay star formation.     

Expansion motions in the inner parts of the galaxy

As well as the high velocity expansion features already known in the inner parts of the galaxy, there also seem to be expansion features at low velocities. Two new features with velocities of -27 km s(-1) and -14 km s(-1) at a distance of about 4.5 kpc are identified in this article and their relationship to the other expanding features is discussed.     

The discovery of a galaxy-wide superwind from a young massive galaxy at redshift z approximately 3

High-velocity galactic outflows, driven by intense bursts of star formation and black hole accretion, are processes invoked by current theories of galaxy formation to terminate star formation in the most massive galaxies and to deposit heavy elements in the intergalactic medium. From existing observational evidence (for high-redshift galaxies) it is unclear whether such outflows are localized to regions of intense star formation just a few kiloparsecs in extent, or whether they instead have a significant impact on the entire galaxy and its surroundings. Here we present two-dimensional spectroscopy of a star-forming galaxy at redshift z = 3.09 (seen 11.5 gigayears ago, when the Universe was 20 per cent of its current age): its spatially extended Lyalpha line emission appears to be absorbed by H i in a foreground screen covering the entire galaxy, with a lateral extent of at least 100 kpc and remarkable velocity coherence. This screen was ejected from the galaxy during a starburst several 10(8) years earlier and has subsequently swept up gas from the surrounding intergalactic medium and cooled. This demonstrates the galaxy-wide impact of high-redshift superwinds.