X射线选射电噪活动星系核的多波段性质(英文)

基于被ROSAT全天区巡天观测和射电 4.85GHz巡天观测同时探测到的活动星系核的大样本 ,研究了X射线选的射电噪活动星系核的多波段性质 .通过分析该样本中的活动星系核的宽波段能量分布 ,确认了来自射电、光学和X射线波段的辐射光度之间的显著相关性 .这种相关性对于类星体、赛弗特、蝎虎座天体和射电星系是有区别的 .同时 ,探讨了从光学到X射线波段之间的谱指数与红移以及 50 0 0 和 4.85GHz处的单色光度的相关性     

亮红外星系NGC 1614中多谱线示踪的致密分子气体

利用高空间分辨率的¹²CO(1-0)、¹³CO(1-0)、¹²CO(3-2)、¹²CO(6-5)、HCN(3-2)、\lk HCN(4-3)、 HCO⁺(3-2)和HCO⁺(4-3)分子谱线的ALMA (Atacama Large Millimeter/ submillimeter Array)归档数据, 来研究近邻亮红外星系NGC 1614的分子气体性质, 尤其是致密分子气体的性质. 在高分辨率分子气体谱线的积分强度图中, 在星系中心区域($<$ 1kpc)可以看到环状结构, 分子气体主要分布于星系中心区域, 核区分子气体含量较少. ¹²CO(1-0)显示出向南部、 北部以及东南部的延展结构, 高阶的CO ($J \ge$ 3, J为转振能级量子数)分子谱线和致密分子HCN、HCO⁺谱线显示, 较致密的分子气体主要集中于星系中心区域. HCN(4-3)/¹²CO(1-0)和HCN⁺(4-3)/¹²CO(1-0)积分强度比值图显示, 致密分子气体主要集中于中心区域的环状结构上. HCN/HCO⁺强度比值的分布变化表明星暴环的不同区域可能具有不同的激发条件. HCN/HCO⁺(4-3)强度比值分布在环的东、西部(sim0.44 pm 0.04)高于环的南、北部(sim0.35 pm 0.03). HCN/HCO⁺(3-2)强度比值较高的区域(sim0.38 pm 0.04)分布在HCN(3-2)峰值位置, 而环的西北、东南部强度比值相对较低(sim0.3 pm 0.03). 对于中心不同区域 HCN/HCO⁺比值变化的原因进行了讨论.     

X线选射电噪活动星系核的多波段性质

基于被ROSAT全天区巡天观测和射电4．85GHz巡天观测同时探测到的活动星系核的大样本,研究了X射线选的射电噪活动星系核的多波段性质．通过分析该样本中的活动星系核的宽波段能量分布,确认了来自射电、光学和X射线波段的辐射光度之间的显著相关性．这种相关性对于类星体、赛弗特、蝎虎座天体和射电星系是有区别的．同时,探讨了从光学到X射线波段之间的谱指数与红移以及5000A和4．85GHz处的单色光度的相关性．     

星系团PKS 0745-191中射电气体对X射线气体的加热

对星系团中相对论性粒子的能量演化做了数值计算，在此基础上，联合分析Chandra卫星数据和VLA射电观测结果，计算了星系团PKS0745-191中高能射电气体对X射线气体的加热作用，发现在射电气体幂律谱能量下限为0.001erg时，射电气体对X射线气体的加热不足以补充X射线气体的辐射能损．然后在计算研究了不同能量下限时射电气体对X射线气体的加热作用，并估计了射电气体的能量下限．     

S5 2007+777的射电性质研究

S5 2007+777是一个典型的低峰值频率的蝎虎天体,该天体具有kpc尺度的X射线喷流,文献中利用模型估算的方法,得出X射线波段的多普勒因子达到13.0,从而喷流尺度可以达到Mpc量级.在此,搜集了有关S5 2007+777的欧洲甚长基线射电干涉网(European VLBI Network, EVN)高分辨率档案数据、美国甚长基线射电干涉网(Very Long Baseline Array, VLBA) 15 GHz观测数据等,研究了喷流的射电结构、亮温度、自行等方面的性质,发现该源的甚长基线干涉测量(Very Long Baseline Interferometry,VLBI)不同波段的喷流方向一致,但与文献中给出的kpc尺度的X射线喷流和甚大阵(Very Large Array, VLA)射电喷流方向存在一定的差异,说明该源的喷流辐射存在多普勒增亮效应.由VLBI观测得到的亮温度,估算了该源的射电多普勒因子的平均值及中值均为5.0,此值小于文献中X射线波段的多普勒因子,但与文献中利用其他方法得到的射电波段多普勒因子是一致的;另外,对多历元观测数据的拟合发现此源相同波段的各个成分在长历元上没有明显的自行,短历元上的自行甚至是视超光速运动.这可能是由低表面亮度成分中心位置的转移造成的.这同时也验证了之前估算的射电多普勒因子不是很大,小于X射线波段多普勒因子的结论.利用所得到的射电多普勒因子,发现该源具有较大尺度的本征射电喷流,可达到0.5 Mpc,由于这里使用的是均值,因此说明该源也有可能具有接近巨射电星系尺度的喷流.     

快速射电暴寄主星系色散量的估计

定位快速射电暴(Fast Radio Burst, FRB)以及确认其寄主星系至今仍是一个具有挑战性的难题,截至2021年4月已确认13个快速射电暴的寄主星系,其中只有3个重复暴,其余都是非重复暴.快速射电暴的寄主星系对快速射电暴起源的探索起着非常重要的作用,约束着快速射电暴前身星模型.对这些已确认寄主星系的FRB进行研究,发现FRB寄主星系对色散量(Dispersion Measure, DM)的贡献在一定范围内波动(0–240 pc·cm-3),并且寄主星系对DM的贡献与寄主星系的性质(恒星形成率、金属丰度)也可能具有关联性.寄主星系恒星形成率、金属丰度与色散量的统计关系对FRB邻近环境的研究有着重要意义.     

由对FRⅡ射电星系的X射线观测试预言射电噪活动星系核的X射线喷流

在早期的文章中，基于耀变体（Blazar)的知识，我们预言了在射电噪活动星系核（AGN）中心10kpc范围内X射线喷流的存在。钱得拉（Chandra)卫星最近对低功率射电星系的X射线观测与我们的预言相一致。在本文中我们研究了kpc尺度喷流中的电子加速，并建议通过对强的FRⅡ射电星系中所预言的X射线喷流的钱得拉卫星的X射线的观测，来研究红的耀变体中的康普顿冷却以及在内部致密喷流和大尺度延伸喷流间环境的不同。以上的研究可以进一步检验我们的关于射电噪活动星系核中kpc尺度X射线喷流的模型。     

Seyfert 2型星系中的星暴活动

星暴和活动星系核之间的联系是活动星系研究领域最重要、最活跃的研究课题之一。Seyfert星系由于距离较近、数目较多和相对低的核活动,已成为研究星暴和活动星系核之间联系的理想天体。综述了活动星系核中存在星暴的观测证据和Seyflert2型星系核区星暴活动的最新研究结果,着重讨论了存在两类Seyflert2型星系(一类是被遮挡的Seyfert1型星系,另一类是“真正”的Seyfert2型星系即不存在宽线区的Seyfert2型星系)的可能性．通过比较具有和不具有偏振宽线的Seyflert2型星系在红外、射电、光学和X射线光谱性质的差别,发现具有偏振宽线的Seyfert2型星系在本质上和Seyflert1型星系是同一类天体,差别只在于观测者视线方向的不同;而不具有偏振宽线的Seyfert2型星系是一些星系核活动较弱而星暴活动占主导的天体,这些星系从射电、红外、光学到硬X射线,都具有和星暴星系相似的性质。由于这些星系中核的吸积率将比Seyflert1型星系低近两个量级,因而它们很有可能是一些没有宽发射线区的Seyfert2型星系,即所谓的“真正”Seyflert2型星系。     

由对FRⅡ射电星系的X射线观测试预言射电噪活动星系核的X射线喷流

在早期的文章中,基于耀变体(Blazar)的知识,我们预言了在射电噪活动星系核(AGN)中心10 kpc范围内X射线喷流的存在.钱得拉(Chandra)卫星最近对低功率射电星系的X射线观测与我们的预言相一致.在本文中我们研究了kpc尺度喷流中的电子加速,并建议通过对强的FR Ⅱ射电星系中所预言的X射线喷流的钱得拉卫星的X射线的观测,来研究红的耀变体中的康普顿冷却以及在内部致密喷流和大尺度延伸喷流间环境的不同.以上的研究可以进一步检验我们的关于射电噪活动星系核中kpc尺度X射线喷流的模型.     

发射线星系[OⅡ]λ3727/Hα谱线流量比的研究

利用从斯隆数字巡天(Sloan Digital Sky Survey,简称SDSS)第4次释放的光谱数据中选取的10~5个发射线星系样本,研究了[O_Ⅱ]λ3727/Hα流量比与星系尘埃消光、气体电离态和金属丰度的关系.发现尘埃消光改正对[O_Ⅱ]λ3727/Hα谱线流量比影响显著,消光改正前、后的[O_Ⅱ]λ3727/Hα谱线流量比的中值分别为0.48和0.89;尘埃消光改正后,F([O_Ⅱ]λ3727)-F(Hα)的弥散显著减小.贫金属星系的[O_Ⅱ]λ3727/Hα谱线流量比随星系气体的电离度增高而减小,而富金属星系不存在这种关系.另外,[O_Ⅱ]λ3727/Hα流量比与星系金属丰度相关.当12+lg(O/H)8.5时,星系[O_Ⅱ]λ3727/Hα流量比随金属丰度增加而下降;12+lg(O/H)8.5的星系,谱线流量比与金属丰度正相关.最后,利用气体电离度参数和星系的金属丰度,给出了计算不同类型星系[O_Ⅱ]λ3727/Hα流量比的公式.LAMOST望远镜将观测到大量红移z0.4的星系光谱,利用该公式可以给出星系的[O_Ⅱ]λ3727/Hα流量比,从而可以利用[O_Ⅱ]λ3727谱线流量计算z0.4星系的恒星形成率.     

Gas dynamic stripping and X-ray emission of cluster elliptical galaxies

Detailed three-dimensional numerical simulations of an elliptical galaxy orbiting in a gas-rich cluster of galaxies indicate that gas dynamic stripping is less efficient than the results from previous, simpler calculations by Takeda et al. and Gaetz et al. implied. This result is consistent with X-ray data for cluster elliptical galaxies. Hydrodynamic torques and direct accretion of orbital angular momentum can result in the formation of a cold gaseous disc, even in a non-rotating galaxy. The gas lost by cluster galaxies via the process of gas dynamic stripping tends to produce a colder, chemically enriched cluster gas core. A comparison of the models with the available X-ray data of cluster galaxies shows that the X-ray luminosity distribution of cluster galaxies may reflect hydrodynamic stripping, but also that a purely hydrodynamic treatment is inadequate for the cooler interstellar medium near the centre of the galaxy.     

A statistically selected Chandra sample of 20 galaxy clusters – II. Gas properties and cool core/non-cool core bimodality

We investigate the thermodynamic and chemical structure of the intracluster medium (ICM) across a statistical sample of 20 galaxy clusters analysed with the Chandra X-ray satellite. In particular, we focus on the scaling properties of the gas density, metallicity and entropy and the comparison between clusters with and without cool cores (CCs). We find marked differences between the two categories except for the gas metallicity, which declines strongly with radius for all clusters  ( Z ∝ r ^−0.31)  , outside  ∼0.02 r ₅₀₀  . The scaling of gas entropy is non-self-similar and we find clear evidence of bimodality in the distribution of logarithmic slopes of the entropy profiles. With only one exception, the steeper sloped entropy profiles are found in CC clusters whereas the flatter slope population are all non-CC clusters. We explore the role of thermal conduction in stabilizing the ICM and conclude that this mechanism alone is sufficient to balance cooling in non-CC clusters. However, CC clusters appear to form a distinct population in which heating from feedback is required in addition to conduction. Under the assumption that non-CC clusters are thermally stabilized by conduction alone, we find the distribution of Spitzer conduction suppression factors, f _c, to be lognormal, with a log (base 10) mean of  −1.50 ± 0.03  (i.e.   f _c= 0.032  ) and log standard deviation  0.39 ± 0.02  .     

Evolution of globular cluster systems in three galaxies of the Fornax cluster

We studied and compared the radial profiles of globular clusters and of the stellar bulge component in three galaxies of the Fornax cluster observed with the WFPC2 of the Hubble Space Telescope ( HST ). The stars are more concentrated toward the galactic centres than globular clusters, in agreement with what has already been observed in many other galaxies: if the observed difference is the result of evolution of the globular cluster systems starting from initial profiles similar to those of the halo–bulge stellar components, a relevant fraction of their initial mass (74, 47 and 52 per cent for NGC 1379, 1399 and 1404, respectively) should have disappeared in the inner regions. This mass has probably contributed to the nuclear field population, local dynamics and high-energy phenomena in the primeval life of the galaxy. An indication in favour of the evolutionary interpretation of the difference between the globular cluster system and stellar bulge radial profiles is given by the positive correlation we found between the value of the mass lost from the globular cluster system and the central galactic black hole mass in the set of seven galaxies for which these data are available.     

The X-ray properties of optically selected z > 0.6 clusters in the European Southern Observatory Distant Cluster Survey

We present XMM–Newton observations of three optically selected   z > 0.6  clusters from the European Southern Observatory (ESO) Distant Cluster Survey (EDisCS), comprising the first results of a planned X-ray survey of the full EDisCS high-redshift sample. The EDisCS clusters were identified in the Las Campanas Distant Cluster Survey as surface brightness fluctuations in the optical sky and their masses and galaxy populations are well described by extensive photometric and spectroscopic observations. We detect two of the three clusters in the X-ray and place a firm upper limit on diffuse emission in the third cluster field. We are able to constrain the X-ray luminosity and temperature of the detected clusters and estimate their masses. We find that the X-ray properties of the detected EDisCS clusters are similar to those of X-ray-selected clusters of comparable mass and – unlike other high-redshift, optically selected clusters – are consistent with the T –σ and   L _X–σ  relations determined from X-ray-selected clusters at low redshift. The X-ray determined mass estimates are generally consistent with those derived from weak-lensing and spectroscopic analyses. These preliminary results suggest that the novel method of optical selection used to construct the EDisCS catalogue may, like selection by X-ray luminosity, be well suited for identification of relaxed, high-redshift clusters whose intracluster medium is in place and stable by   z ∼ 0.8  .