A review of diagnostic emission line ratios in the Narrow Line Region of Active Galactic Nuclei

The availability of new observing facilities both from ground and space such as the Keck 10m telescope and the Hubble Space Telescope is casting new light on the spectroscopic investigation of emission line galaxies. In particular, it is now possible to detect spectra with a significantly improved signal to noise ratio in a very wide wavelength range, from the ultraviolet to the near infrared (HST, Keck) and beyond (ISO is unveiling the far infrared domain). As we move to high redshifts, however, it is more likely that the observed spectra are given by the contribution of different components in the galaxy: in particular, this may be the case if an Active Galactic Nucleus (AGN hereafter) emitting a power-law continuum is surrounded by regions with strong star formation activity. The identification of the source which ionizes the line emitting regions is then complicated by the fact that we are observing the integrated spectrum from regions which are ionized by different sources. In this paper we wish to review which line ratios may be used in order to discriminate between photoionization by young stars and power-law continuum in the wavelength range from 1200 Å to 100 μm. To this aim we used the photoionization code Cloudy (Ferland 1996) to present a series of diagnostic diagrams showing the dependence of emission line ratios on the main input parameters of photoionization models in the case of one component models with gaseous clouds ionized by (1) a stellar continuum typical of an HII region and (2) a power-law continuum typical of an AGN: these line ratios are plotted as isoratio maps for different values of the hydrogen density, ionization parameter and slope of the power-law continuum. We then show how the results may be affected by more realistic assumptions about the environment of the ionized gas: to this aim, we show the effects on selected line ratios of (a) the presence of two populations of clouds with different densities and (b) an AGN surrounded by regions with strong star formation activity.     

A short introduction to broad and variable iron lines around black holes

Accreting black holes often show iron line emission in their X‐ray spectra. When this line emission is very broad or variable then it is likely to originate from close to the black hole. The theory and observations of such broad and variable iron lines are briefly reviewed here. In order for a clear broad line to be found, one or more of the following have to occur: high iron abundance, dense disk surface and minimal complex absorption. Several excellent examples are found from observations of Seyfert galaxies and Galactic Black Holes. In several cases there is strong evidence that the black hole is rapidly spinning. Further examples are expected as more long observations are made with XMM‐Newton, Chandra and Suzaku. Intriguing instances of rapid variability of some narrow iron lines, both emission and absorption, have been reported. These may reflect variations in the irradiation or motion of physical structures on the accretion disk. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Prospects and requirements for measurements of extragalactic γ-ray lines

A brief summary is presented of requirements for the measurements of extragalactic γ-ray lines. The electron-positron annihilation line at 511 keV represents the best prospect, and although this line is greatly broadened in active galactic nuclei, a narrow line should be present in clusters of galaxies and radio lobes as a result of prior AGN activity. The strongest fluxes should be of the order of 10⁻⁴ photons cm⁻² s⁻¹ from the closest extended sources.     

从MPIfR的校准数据看活动星系核的变化

从过去6年里MPIfR的VLBI校准数据中挑出有20次以上记录的15个样本源进行了初步分析，结果表明在研究活动星系核（AGN）的变化中，这些以及由其它射电望远镜或系统所积累的类似校准数据是很有用的．     

Photoionising shocks in SNRs and AGN

A high velocity radiative shock, or one moving into high-metallicity gas, provides an efficient means to generate a strong local UV photon field. The optical emission from the shock and precursor region is dominated by the photoionised gas, rather than by the cooling region, and the total optical + UV emission scales as the mechanical energy flux through the shock. In this paper, such models are applied to oxygen-rich supernova remnants and AGN. For AGN, the degree of magnetic support in the post-shock gas is an important parameter. LINER and cooling flow spectra can be understood as resulting from high velocity shocks without precursors, while Seyfert 1.5–2 galaxy emission line ratios result from high velocity shocks with their photoionised precursor HII regions. This model explains the problem of the high electron temperatures observed in both classes of object.     

HESS observations of extragalactic objects

The HESS experiment (High Energy Stereoscopic System), consisting of four imaging atmospheric Cherenkov telescopes (IACTs) in Namibia, has observed many extragalactic objects in the search for very high energy (VHE) γ-ray emission. These objects include active galactic nuclei (AGN), notably Blazars, Seyferts, radio galaxies, starburst galaxies and others. Beyond the established sources, γ-ray emission has been detected for the first time from several of these objects by HESS, and their energy spectra and variability characteristics have been measured. Multi-wavelength campaigns, including X-ray satellites, radio telescopes, and optical observations, have been carried out for AGNs, in particular for PKS 2155-304, H 2356-309 and 1ES 1101-232, for which the implications concerning emission models are presented. Also results from the investigations of VHE flux variability from the giant radio galaxy M 87 are shown. For the HESS Collaboration.     

活动星系核的演化与宇宙学红移

通过搜集了457个活动星系核样本,根据活动星系核的演化实质是指宇宙时标上的变化,讨论了红移量与活动星系核演化的关系,最终证明了活动星系核的演化分为两个序列:(1)从类星体到Seyfert星系之间的演化;(2)平谱射电类星体(FSRQ)—BL Lac天体—射电星系(RG)的演化。     

活动星系核的伽玛辐射和宇宙标准烛光

编辑了一个样本,其中包括71个Gev伽玛射线噪的活动星系核(14个BL Lac天体和57个平谱射电类星体),53个FRⅠ型射电星系和63个FRⅡ型射电星系。文章采用了非线性最小二乘法来拟合这个样本。当假设Mv=-23.0时,得到一个达到最佳拟合的哈勃常数,其拟合值为H0=71.5±3.8kms-1Mpc-1。该值与通过哈勃望远镜关键计划所得到的哈勃常数值H0=71.5±8kms-1Mpc-1符合得很好。其结果表明活动星系核的Gev伽玛辐射可以被用作宇宙标准烛光。     

射电源的谱指数

文章研究了162个射电源,其中包括了47个BL Lacs ,21个galaxies ,94个平谱射电类星体( FSRQs ) ,这些源是通过Michigan大学的26m的射电望远镜观测的。大多数源都包含了3个波段的观测数据:4 .8GHz ,8GHz和14 .5GHz。文中计算了3个子类的平均的流量密度,并且得到了相应的谱指数(αwei) ,αBL=0 .08±0 .28 ,αGAL=-0 .91±0 .32 ,αFSRQ=-0 .14±0 .4。同时也讨论了这些源的射电性质,其中包含了谱指数,流量密度和红移之间的关系,流量密度和谱指数之间的关系。     

Reverberation mapping analysis of the broad-line region in Seyfert galaxy NGC 4151

Using the optical data of the 1993 international watch of NGC 5141, we made follow-up reverberation mapping analyses of its broad line region (BLR). We found the transfer function of the BLR for the 1993 data is entirely different from that for the 1988 international watch. We conclude that the structure of the BLR had changed in those 5 years and it is this change in structure that is responsible for the very different sizes of the BLR deduced from the two sets of data.