Precision era of the kinetic Sunyaev–Zel'dovich effect: simulations, analytical models and observations and the power to constrain reionization     

Pengjie Zhang  Ue-Li Pen  Hy Trac 《Monthly notices of the Royal Astronomical Society》2004,347(4):1224-1233

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Scattering of elastic wave by a partially sealed cylindrical shell embedded in poroelastic medium     

Liu Gan‐Bin  Xie Kang‐He  Yao Hai‐lin 《国际地质力学数值与分析法杂志》2005,29(11):1109-1126

Scattering of an elastic wave by a cylindrical shell embedded in poroelastic medium is investigated theoretically with the assumption that the shell material is also a porous elastic medium. The porous medium is modellized via Biot's theory and the scattering by cylindrical shell is expressed by the definition of scattering matrix. The normal mode expansion technique is employed for analysing the scattering field, and the asymptotic solutions of displacements, stresses and pore pressure are derived. Two limiting cases‐scattering by a poroelastic cylinder in Biot medium and a elastic cylindrical shell in elastic medium are obtained from the general solutions. The dispersion curves of displacement amplitude at the interface of shell and medium is compared with the case of elastic shell. The scattering amplitude associated with the fast, slow and transverse waves are identified by numerical simulation. Furthermore, the influence of the poroelastic property of shell material on scattering amplitude is analysed. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

The brightest OH maser in the sky: A flare of emission in W75 N     

A. V. Alakoz  V. I. Slysh  M. V. Popov  I. E. Val’tts 《Astronomy Letters》2005,31(6):375-379

A flare of maser radio emission in the 1665-MHz OH line with a flux density of about 1000 Jy was discovered in the star-forming region W75 N in 2003. At the time of its observations, it was the strongest OH maser in the entire history of research since the discovery of cosmic OH masers in 1965. The linear polarization of the flare emission reached 100%. A weaker flare with a flux density of 145 Jy was observed in this source in 2000–2001; this was probably a precursor of the intense flare. The intensity of two other spectral features decreased when the flare emerged. This change in the intensity of the emission from maser condensations (a brightening of some of them and a weakening of others) can be explained by the passage of a magnetohydrodynamic shock through regions of enhanced gas concentration.  相似文献   

The baseline intracluster entropy profile from gravitational structure formation     

G. Mark Voit  Scott T. Kay  Greg L. Bryan 《Monthly notices of the Royal Astronomical Society》2005,364(3):909-916

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An old galaxy group: Chandra X-ray observations of the nearby fossil group NGC 6482     

Habib G. Khosroshahi  Laurence R. Jones  Trevor J. Ponman 《Monthly notices of the Royal Astronomical Society》2004,349(4):1240-1250

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The 21-cm forest     

Steven R. Furlanetto 《Monthly notices of the Royal Astronomical Society》2006,370(4):1867-1875

We examine the prospects for studying the pre-reionization intergalactic medium (IGM) through the so-called 21-cm forest in spectra of bright high-redshift radio sources. We first compute the evolution of the mean optical depth τ for models that include X-ray heating of the IGM gas, Wouthuysen–Field coupling, and reionization. Under most circumstances, the spin temperature T _S grows large well before reionization begins in earnest; this occurs so long as the X-ray luminosity of high-redshift starbursts (per unit star formation rate) is comparable to that in nearby galaxies. As a result,  τ≲ 10⁻³  throughout most of reionization, and background sources must sit well beyond the reionization surface in order to experience absorption that is measurable by square-kilometre class telescopes. H  ii regions produce relatively large 'transmission gaps' and may therefore still be observable during the early stages of reionization. Absorption from sheets and filaments in the cosmic web fades once T _S becomes large and should be rare during reionization. Minihaloes can produce strong (albeit narrow) absorption features. Measuring their abundance would yield useful limits on the strength of feedback processes in the IGM as well as their effect on reionization.  相似文献   

A statistically selected Chandra sample of 20 galaxy clusters – I. Temperature and cooling time profiles     

Alastair J. R. Sanderson  Trevor J. Ponman  Ewan O'Sullivan 《Monthly notices of the Royal Astronomical Society》2006,372(4):1496-1508

We present an analysis of 20 galaxy clusters observed with the Chandra X-ray satellite, focusing on the temperature structure of the intracluster medium and the cooling time of the gas. Our sample is drawn from a flux-limited catalogue but excludes the Fornax, Coma and Centaurus clusters, owing to their large angular size compared to the Chandra field of view. We describe a quantitative measure of the impact of central cooling, and find that the sample comprises nine clusters possessing cool cores (CCs) and 11 without. The properties of these two types differ markedly, but there is a high degree of uniformity amongst the CC clusters, which obey a nearly universal radial scaling in temperature of the form   T ∝ r ^∼0.4  , within the core. This uniformity persists in the gas cooling time, which varies more strongly with radius in CC clusters  ( t _cool∝ r ^∼1.3)  , reaching   t _cool < 1 Gyr  in all cases, although surprisingly low central cooling times (<5 Gyr) are found in many of the non-CC systems. The scatter between the cooling time profiles of all the clusters is found to be remarkably small, implying a universal form for the cooling time of gas at a given physical radius in virialized systems, in agreement with recent previous work. Our results favour cluster merging as the primary factor in preventing the formation of CCs.  相似文献   

The epoch of reionization     

Andrew J. Benson  Naoshi Sugiyama  Adi Nusser  Cedric G. Lacey 《Monthly notices of the Royal Astronomical Society》2006,369(3):1055-1080

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Jets in the Fanaroff–Riley class I radio galaxies PKS B1234−723, MRC 1452−517 and PKS B2148−555     

Ben D.Lloyd  Paul A.Jones 《Monthly notices of the Royal Astronomical Society》2002,331(3):717-730

We present radio observations made with the Australia Telescope Compact Array to study the jets and lobes of three Fanaroff–Riley class I (FR I) radio galaxies: PKS B1234−723, 1452−517 and B2148−555. The total intensity and polarization radio images of the FR I jets are used to determine jet brightness and width variations, magnetic field structure and fractional polarization. The equipartition pressure is determined as a function of distance from the galaxies to probe the intergalactic medium.  相似文献   

Thermal characteristics of anisotropic media with inclusions   总被引：1，自引：0，他引：1  

I. M. Artemieva  E. M. Chesnokov 《Geophysical Journal International》1991,107(3):557-562

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