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1.
自从首次发现河外星系OH超脉泽以来，30多年(特别是近10年)中对河外星系OH超脉泽的观测和研究取得了极大的进展。到目前为止已发现106个河外星系OH超脉泽，其中包括59个较高红移的源。对河外星系OH超脉泽的观测和研究，是探测和研究其所成协的活动星系核、星暴星系的中央源和拱核盘的有效工具。主要评述对河外星系OH超脉泽的搜索、观测和理论研究现状。 相似文献
2.
对一些OH／IR星的拱星OH脉泽的观测结果表明,在双峰结构谱线轮廓上常常可以发现一些小峰叠加在双峰上,即在谱线轮廓的双峰结构中的每个峰是由几个小峰叠加而成的．从脉泽的辐射转移方程和拱星包层的速度结构出发,研究拱星OH脉泽辐射频谱的轮廓特征,提出多重分离的膨胀拱星亮模型,很好地解释了双峰结构的奇特观测现象． 相似文献
3.
本文提出OH超脉泽源的一个具体模型,在该模型中OH超脉泽源由非饱和的球型子源组成.在此估算出超脉泽星系致密射电核的尺度和连续谱亮温度,以及OH源距星系核的最小非饱和距离.计算表明,OH超脉泽源所包含的子源数目可能相当大.R_H～log ρ_(25μm)/ρ_(60μm)图、log L_(OH)/L_(IR)～log ρ_(25μm)/ρ_(60μm)图和其它结果显示,有一部分OH超脉泽源很可能是弱饱和的,本文对此作了解释. 相似文献
4.
介绍了近年来河外H2O超脉泽的主要观测结果。H2O超脉泽通常起源于活动星系核中央的拱核盘。它们主要寄生在Serfert2星系或低电离核区。至今为止，已有20个星系探测到H2O超脉泽。脉泽辐射的各向同性光度为10－6000L。所有超脉泽星系显示出核的活动，显然，脉泽是由核活动所产生的射电和X射线光子或激波来抽运的。H2O超脉泽倾向存在于高倾斜度的星系，这使得沿视线上的分子柱密度增高，产生足够大的放大光深。最有可能产生H2O超脉泽辐射的星系应有一个包含着射电源的侧向的分子盘以及一个适当的抽运机制。 相似文献
5.
介绍了近年来河外Ｈ２Ｏ超脉泽的主要观测结果。Ｈ２Ｏ超脉泽通常起源于活动星系核中央的拱核盘。它们主要寄生在 Ｓｅｒｆｅｒｔ ２星系或低电离核区。至今为止，已有２０个星系探测到Ｈ２Ｏ超脉泽。脉泽辐射的各向同性光度为１０～６０００Ｌ⊙。所有超脉泽星系显示出核的活动，显然，脉泽是由核活动所产生的射电和Ｘ射线光子或激波来抽运的。Ｈ２Ｏ超脉泽倾向存在于高倾斜度的星系，这使得沿视线上的分子柱密度增高，产生足够大的放大光深。最有可能产生Ｈ２Ｏ超脉泽辐射的星系应有一个包含着射电源的侧向的分子盘以及一个适当的抽运机制。 相似文献
6.
自从在活动星系核NGC4945的视线方向上发现第一个河外H2O超脉泽源以来，迄今为止已发现了19个河外H2O超脉泽源，对与活动星系核成协和河外H2O超脉泽源及分子谱线的观测和研究是探测和研究活动星系核核区中央源，拱核气体和尘埃环性质的非常有效的工具，主要评述对河外H2O超脉泽源及与其相关分子谱线的搜索，观测和理论研究现状。 相似文献
7.
俞志尧 《中国科学院上海天文台年刊》2002,(23):102-106
利用法国巴黎天台的南锡射电望远镜对ON2西部区域OH1612MHz脉泽首次进行观测，观测结果表明，西部区域的OH1612MHz脉泽的辐射频谱为典型的单峰结构。结合模型对西部区域的OH1612MHz脉泽谱线频谱图进行分析和研究。利用薄盘模型。得到相应于ON2西部区域的OH1612MHz脉泽单峰脉泽斑的位置在r=112.5AU,Y=7.6AU,其Keplerian运动速度为Ur=10.6kg/s,V1=-9.4km/s。 相似文献
8.
俞志尧 《中国科学院上海天文台年刊》2002,(1)
利用法国巴黎天文台的南锡射电望远镜对ON2西部区域OH16 12MHz脉泽首次进行观测 ,观测结果表明 ,西部区域的OH16 12MHz脉泽的辐射频谱为典型的单峰结构。结合模型对西部区域的OH16 12MHz脉泽谱线频谱图进行分析和研究。利用薄盘模型 ,得到相应于ON2西部区域的OH16 12MHz脉泽单峰脉泽斑的位置在r =112 .5AU ,Y =7.6AU ,其Keplerian运动速度为Ur=10 .6km s ,Vt =- 9.4km s . 相似文献
9.
本文在“OH/IR脉泽源的空间分布和光度函数”一文的基础上,对其所用的127个已有光学或红外证认的OH脉泽源的空间运动特性进行了分析,找到各类OH/IR脉泽源的视向速度与银河系较差自转运动的偏离以及各种速度分离下源的运动特点,同时利用文[1]所得的已证认OH/IR源的空间真实密度分布,导出了它们的速度分布模型N(l,v)。对与新证认的非IRC红外源(通常是在更长波长上观测到的)成协的OH/IR源发现有一以银心为心的约为50km/s的径向膨胀运动。文章最后对已证认和未证认的OH/IR脉泽源的差别和联系进行了讨论。 相似文献
10.
利用法国巴黎天文台的南锡射电望远镜对ON2中部以西区域OH1665和1667MHz脉泽进行观测，结合模型对中部以西区域的OH1665和1667MHz脉泽谱线频谱图进行分析和研究、利用薄盘模型，得到相应于ON2中部以西区域的OH1665和1667MHz峰的脉泽斑的位置及其Keplerian运动速度。 相似文献
11.
Zhi-Yao Yu Shanghai Astronomical Observatory Chinese Academy of Sciences Shanghai National Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2005,5(2):159-164
Many galaxies are thought to contain massive black holes, with masses in excess of ten million solar masses, at their centres and warped circumnu-clear toruses. The best evidence comes from observing gas or masers rotating rapidly within a circumnuclear torus surrounding a central body. Here we report on the first MERLIN observations of line emission from the OH megamaser toward IRAS 10173+0828. The position of peak flux contours of the OH megamaser is consistent with that of the continuum in IRAS 10173+0828. This means that the OH megamaser is a diffuse unsaturated maser which could amplify the diffuse 18 cm continuum emission with an amplification factor of order unity. 相似文献
12.
We present a high-resolution kinematical study of the ionized gas in the circumnuclear region of NGC 4314. Our spectra reveal
the presence of a central structure (apparently a ring or torus) located at ∼ 2 arcsec from the nucleus, which we identify
as the shocked interface between the nuclear bar and the gas inside the HII region ring.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
S. Young † C. Packham R. E. Mason J. T. Radomski C. M. Telesco 《Monthly notices of the Royal Astronomical Society》2007,378(3):888-892
We present spatially resolved 10-μm spectra of the nucleus of IC 5063 that are near-diffraction-limited. The observations were obtained with T-ReCS, the mid-infrared (mid-IR) imager and spectrometer on the 8.1-m Gemini South telescope, with the slit aligned at a position angle on the sky along the direction of the cone of narrow-line emission. The spectra cover the nucleus and the inner reaches of the ionization cones at a spatial resolution of approximately 0.4 arcsec (90 pc). Individual spectra, extracted in steps in the spatial direction along the slit, reveal variations in continuum slope and silicate feature profile and depth on subarcsecond scales, illustrating in unprecedented detail the complexity of the circumnuclear regions of this galaxy at mid-IR wavelengths. The dust population in the vicinity of the narrow-line region, north-west of the nuclear position, is significantly warmer than that to the south-east of the nucleus. This is consistent with an observation of the cooler dust associated with the outer reaches of the postulated torus that obscures the type 1 nucleus in this object. 相似文献
14.
A. Pappa † I. Georgantopoulos G.C. Stewart A.L. Zezas ‡ 《Monthly notices of the Royal Astronomical Society》2001,326(3):995-1006
We present an X-ray spectral analysis of a sample of eight bona fide Seyfert 2 galaxies, selected on the basis of their high [O iii ] λ 5007 flux, from the Ho et al. spectroscopic sample of nearby galaxies. We find that, in general, the X-ray spectra of our Seyfert 2 galaxies are complex, with some of our objects having spectra different from the 'typical' spectrum of X-ray selected Seyfert 2 galaxies. Two (NGC 3147 and 4698) show no evidence for intrinsic absorption. We suggest that this is a result of the fact that when the torus suppresses the intrinsic medium and hard energy flux, underlying emission from the host galaxy, originating in circumnuclear starbursts, and scattering from warm absorbers contributes in these energy bands more significantly. Our ASCA data alone cannot discriminate whether low-absorption objects are Compton-thick active galactic nuclei (AGNs) with a strong scattered component or lack an obscuring torus. The most striking example of our low absorption Seyfert 2 is NGC 4698. Its spectrum could be explained by either a dusty warm absorber or a lack of broad-line clouds so that its appearance as a Seyfert 2 is intrinsic and not a result of absorption. 相似文献
15.
J. Fritz † A. Franceschini E. Hatziminaoglou 《Monthly notices of the Royal Astronomical Society》2006,366(3):767-786
We describe improved modelling of the emission by dust in a toroidal-like structure heated by a central illuminating source within active galactic nuclei (AGNs). We have chosen a simple but realistic torus geometry, a flared disc, and a dust grain distribution function including a full range of grain sizes. The optical depth within the torus is computed in detail taking into account the different sublimation temperatures of the silicate and graphite grains, which solves previously reported inconsistencies in the silicate emission feature in type 1 AGNs. We exploit this model to study the spectral energy distributions (SEDs) of 58 extragalactic (both type 1 and type 2) sources using archival optical and infrared data. We find that both AGN and starburst contributions are often required to reproduce the observed SEDs, although in a few cases they are very well fitted by a pure AGN component. The AGN contribution to the far-infrared luminosity is found to be higher in type 1 sources, with all the type 2 requiring a substantial contribution from a circumnuclear starburst. Our results appear in agreement with the AGN unified scheme, because the distributions of key parameters of the torus models turn out to be compatible for type 1 and type 2 AGNs. Further support to the unification concept comes from comparison with medium-resolution infrared spectra of type 1 AGNs by the Spitzer observatory, showing evidence for a moderate silicate emission around 10 μm, which our code reproduces. From our analysis we infer accretion flows in the inner nucleus of local AGNs characterized by high equatorial optical depths ( AV ≃ 100) , moderate sizes ( R max < 100 pc) and very high covering factors ( f ≃ 80 per cent) on average. 相似文献
16.
A model is developed for the H2O maser source observed in the circumnuclear region of the galaxy NGC 4258. The maser emission originates at distances of 0.15–0.29 pc from the center in a thin, cold accretion disk (gas-dust torus) rotating around a supermassive black hole of mass 4 × 107 M ⊙. The conditions for the emergence of an inverse population of the signal 616?523 levels in ortho-H2O working molecules are simulated numerically. The complex line profile, which includes both central and high-velocity components, is calculated. A comparison of the calculations with radiointerferometric and spectrophotometric observations allowed the physical conditions in the emitting region to be determined. 相似文献
17.
C. S. Reynolds K. Iwasawa C. S. Crawford & A. C. Fabian 《Monthly notices of the Royal Astronomical Society》1998,299(2):410-416
We present an ASCA observation of the broad-line radio galaxy 3C 111. The X-ray spectrum is well described by a model consisting of a photoelectrically absorbed power-law form. The inferred absorbing column density is significantly greater than expected on the basis of 21-cm measurements of Galactic H I . Whilst this may be the result of intrinsic absorption from a circumnuclear torus or highly warped accretion disc, inhomogeneities and molecular gas within the foreground giant molecular cloud may also be responsible for some of this excess absorption. We also claim a marginal detection of a broad iron Kα line which is well explained as being a fluorescent line originating from the central regions of a radiatively efficient accretion disc. This line appears weak in comparison to those found in (radio-quiet) Seyfert nuclei. We briefly discuss the implications of this fact. 相似文献
18.
M. Guainazzi W. Marshall A. N. Parmar 《Monthly notices of the Royal Astronomical Society》2001,323(1):75-83
We present two BeppoSAX observations of the bright Seyfert 1 galaxy NGC 3516, performed four months apart (late 1996–early 1997). The earlier spectrum is considerably weaker and harder in the whole 0.1–50 keV energy range. In addition, the warm absorber oxygen features, which were already observed with ROSAT and ASCA , are much less pronounced. The most straightforward explanation is that in 1996 November NGC 3516 was being seen through a substantial ( N H ≃1022 cm−2 ) column of cold material. This is the first confirmation with modern instrumentation that NGC 3516 indeed undergoes phases of strong cold X-ray absorption. We speculate that these intervals may be connected to the onset of the remarkably variable UV absorption system, making NGC 3516 the best known example of a low-luminosity broad absorption line (BAL) quasar. The absorbing matter could be provided by clouds ablated from the rim of the circumnuclear molecular torus, seen at a rather high inclination angle. 相似文献
19.
D. Pérez-Ramírez J. H. Knapen † R. F. Peletier S. Laine R. Doyon † D. Nadeau † 《Monthly notices of the Royal Astronomical Society》2000,317(2):234-248
We present subarcsecond-resolution, ground-based, near-infrared images of the central regions of a sample of 12 barred galaxies with circumnuclear star formation activity, which is organized in ring-like regions typically 1 kpc in diameter. We also present Hubble Space Telescope near-infrared images of 10 of our sample galaxies, and compare them with our ground-based data. Although our sample galaxies were selected for the presence of circumnuclear star formation activity, our broad-band near-infrared images are heterogeneous, showing a substantial amount of small-scale structure in some galaxies, and practically none in others. We argue that, where it exists, this structure is caused by young stars, which also cause the characteristic bumps or changes in slope in the radial profiles of ellipticity, major axis position angle, surface brightness and colour at the radius of the circumnuclear ring in most of our sample galaxies. In seven out of 10 HST images, star formation in the nuclear ring is clearly visible as a large number of small emitting regions, organized into spiral arm fragments, which are accompanied by dust lanes. Near-infrared colour index maps show much more clearly the location of dust lanes and, in certain cases, regions of star formation than single broad-band images. Circumnuclear spiral structure thus outlined appears to be common in barred spiral galaxies with circumnuclear star formation. 相似文献
20.
We present a study of the nearby Seyfert galaxy NGC 3982 using optical,infrared and X-ray data acquired by SDSS,Spitzer and Chandra.Our main results are as follows:(1) A simple stellar population synthesis on the nuclear and circumnuclear SDSS spectra gives unambiguous evidence of young stellar components in both the nuclear and circumnuclear regions.(2) The Spitzer Infrared Spectrograph (IRS) spectrum of the central region (～3") shows a power-law continuum,a silicate emission feature at 9.7 μm,and significant PAH emission features at 7.7,8.6,11.3 and 12.7/zm,suggesting the coexistence of AGN and starburst activities in the central region of NGC 3982.(3) We estimate the star formation rate (SFR) of the circumnuclear (～5"-20") region from the Ha luminosity to be for the active nucleus of NGC 3982 from radio to X-ray,and obtain a bolometric luminosity of Lbol=4.5×1042 erg s-1,corresponding to an Eddington ratio (Lbol/LEdd) of 0.014.The HST image of NGC 3982 shows a nuclear mini-spiral between the circumnuclear starforming region and the nucleus,which could be the channel through which gas is transported to the supermassive black hole from the circumnuclear star-forming region. 相似文献