共查询到20条相似文献，搜索用时 31 毫秒
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Smita Mathur 《Monthly notices of the Royal Astronomical Society》2000,314(4):L17-L20
Narrow Line Seyfert 1 galaxies (NLS1s) are intriguing owing to their continuum as well as emission-line properties. The observed peculiar properties of the NLS1s are believed to be as a result of an accretion rate close to the Eddington limit. As a consequence of this, for a given luminosity, NLS1s have smaller black hole (BH) masses compared with normal Seyfert galaxies. Here we argue that NLS1s might be Seyfert galaxies in their early stage of evolution and as such may be low-redshift, low-luminosity analogues of high-redshift quasars. We propose that NLS1s may reside in rejuvenated, gas-rich galaxies. We also argue in favour of collisional ionization for production of Fe ii in active galactic nuclei. 相似文献
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Byurakan Astrophysical Observatory. Translated from Astrofizika, Vol. 33, No. 3, pp. 403–408, November–December, 1990. 相似文献
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G. Matt 《Astronomische Nachrichten》2008,329(2):151-154
In this paper I will review, in an unavoidably incomplete and biased way, the main results obtained by XMM‐Newton on Active Galactic Nuclei. I will then highlight the major issues still open in which XMM‐Newton can still give important contributions, expecially if the observing programs will shift in the future towards more long exposures of single objects and observations of large samples. I will also argue in favour of a legacy program consisting of good S/N observations of a flux‐limited, sizeable sample of AGN. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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T. Jaakkola 《Astrophysics and Space Science》1977,49(1):99-111
82 compact galaxies with measured redshift present in systems containing partly normal galaxies have been found, using Zwicky's Catalogues and Morphological Catalogue. For them the mean residual redshift
has been obtained. The chance probability for this result is 0.015. A high frequency of compact galaxies among those with large discrepant redshift is remarked. Relatively compact normal galaxies also reveal a positive mean value of
. Redshift is correlated with magnitude in groups and pairs of compact galaxies, this depending in pairs on the linear separation and colours of the components. If a colour difference is present, the bluer member has the larger redshift in general. In contrast with the large luminosity deduced from the redshift for many field compacts, compact galaxies in systems are faint. The majority of the proposed associations between quasars and systems of normal galaxies are shown to be probably physical. 相似文献
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R. A. Kandalian 《Astrophysics》1996,39(3):237-244
An analysis of a sample of OH megamaser galaxies is presented. It is shown that the dependence of LOH on LFIR (far infrared) is not quadratic, as previously assumed, but closer to linear. In megamaser galaxies, LC (radio continuum) LFIR1. Analysis of the data also shows that as the OH emission line width decreases, the absolute values of the pumping efficiency and maser amplification coefficient increase. The radio luminosity of the central component in these galaxies increases with a decrease in the ratio LFIR/LC, whereas the FIR luminosity remains constant. These results will, in all probability, force a reexamination of the questions of pumping and maser emission mechanisms in megamaser galaxies.Translated fromAstrofizika, Vol. 39, No. 3, pp. 417–429, July–September, 1996. 相似文献
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Taniguchi Yoshiaki Shibata Katsunori Wakamatsu Ken-Ichi 《Astrophysics and Space Science》1986,118(1-2):529-530
Four polar ring galaxies discovered in rich clusters of galaxies are presented. Brief comments on their structural properties are given.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984. 相似文献
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The morphological content of Markarian galaxies (MG) in groups and in single galaxies is examined. It is found that MG do
not conform to the long established rule that the relative number of elliptical and lenticular galaxies in groups is higher
than in single galaxies. 相似文献
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We study the role of asymptotic curves in supporting the spiral structure of a N-body model simulating a barred spiral galaxy. Chaotic orbits with initial conditions on the unstable asymptotic manifolds of the main unstable periodic orbits follow the shape of the periodic orbits for an initial interval of time and then they are diffused outwards along the spiral structure of the galaxy. Chaotic orbits having small deviations from the unstable periodic orbits, stay close and along the corresponding unstable asymptotic manifolds, supporting the spiral structure for more than 10 rotations of the bar. Chaotic orbits of different Jacobi constants support different parts of the spiral structure. We also study the diffusion rate of chaotic orbits outwards and find that the orbits that support the outer parts of the galaxy are diffused outwards more slowly than the orbits supporting the inner parts of the spiral structure. 相似文献
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M. Rowan-Robinson 《Monthly notices of the Royal Astronomical Society》2000,316(4):885-900
39 galaxies are now known, from follow-up of faint IRAS sources and from submillimetre observations of high-redshift AGN, with far-infrared luminosities >1013 L⊙ . 13 of these, which have been found in 60- or 850-μm surveys, form an important unbiased subsample. 12 have been found by comparison of 60-μm surveys with quasar or radio galaxy catalogues, or from infrared surveys with colour selection biased towards AGN, while a further 14 have been found through submillimetre observations of known high-redshift AGN. In this paper I argue, on the basis of detailed modelling of the spectral energy distributions of hyperluminous galaxies with accurate radiative transfer models, and from evidence of high gas mass in several cases, that the bulk of the emission from these galaxies at rest frame wavelengths ≥50 μm is caused by star formation. Even after correction for the effects of lensing, hyperluminous galaxies with emission peaking at rest frame wavelengths ≥50 μm are therefore undergoing star formation at rates >103 M⊙ yr−1 and are strong candidates for being primeval galaxies, in the process of a major episode of star formation. 相似文献
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We present a quantitative method of classification of the multi-wavelength morphology of galaxies, elaborated from the nearby
galaxies and usable to high redshift objects. We use the morphological parameters of concentration of light at the galaxy
center and 180°-rotationnal asymmetry, computed in several wavelengths, from ultraviolet (UV) to R band. The variation of these indices with
λ reflects the proportion of young and old stellar populations in galaxies, that is characteristic of every morphological
type: elliptical/lenticular, spiral and irregular. We need to elaborate some templates of these variation spectra from the
study of nearby objects, for an application to distant galaxies.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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S. Charlot 《Astrophysics and Space Science》1994,217(1-2):261-263
Observations of nearby star-forming regions suggest that the initial mass function is deficient in low-mass stars when the ambient star formation rate is high. We investigate the consequences of a truncated initial mass function on the photometric evolution of starburst galaxies using new models of stellar population synthesis. A major prediction with respect to the case of a standard initial mass function is that the spectra of the galaxies become unusually red when the turnoff mass reaches the cutoff of the initial mass function. This red phase can last for more than 109 yr if the lower cutoff is less than 2M
. The amplitude of the reddening depends only weakly on the lower cutoff but increases with the fraction of the galaxy mass involved in the starburst. Such unusually red (V - K > 3.5) post-starburst galaxies can be distinguished from galaxies reddened by dust or with abnormally high metallicities by their unusually strong 4000 Å break and the presence of stellar absorption features typical of late-type giants. 相似文献
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We study a model of mergers affecting only the progenitors of present E/SO. We adopt the standard scenarios of star formation as prescribed by Guiderdoni & Rocca-Volmerange. The merging process is parametrized under the assumptions of(1) self-similarity of the Schechter MF and(2) mass conservation. Nine models are discussed. The predictions are compared with counts ofB
J
,U
+,F
+,N
+ bands. E/SO mergers account for the excess of the faintest blue galaxies without causing excess in redder bands. However, as we no longer have enough mergers at brighter magnitudes, a plain E/SO merging model fits less tightly for the redshift and the colour distributions. Detection effect, a steeper slope of LF may be ways to improve. Our models predict acceptable merger frequencies atz = 0.5 although some models predict more interacting galaxies than observation atz = 0. 相似文献
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1200 strongly flattened galaxies with axis ratio b/a ≤ 0.15 were selected from the UGC catalogue, contained in the Abadumani
Merged Catalogue of Galaxies, and their properties were studied. The possibility of using strongly flattened galaxies and
several other samples of galaxies according to their morphological type as a distance indicator has been examined by the Tully-Fisher
relation. The investigation has shown that angular diameters of strongly flattened as well as flat, seen edge-on galaxies
designated as F and L in the MCG catalogue can be used for the estimation of distance moduli with accuracy O.m7. The distribution of absolute magnitudes of strongly flattened galaxies was approximated by analytic Schechter expression
with main parameters M* = -21.m2 and α = -1.0. The statistical method of the nearest companion applied to the apparent distribution of strongly flattened
galaxies has shown that these galaxies are considerably more frequently found in mixed pairs and multiple systems than spirals.
Published in Astrofizika, Vol. 41, No. 1, pp. 23–34, January-March, 1998. 相似文献