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81.
Kirsty J. Rhook Martin G. Haehnelt 《Monthly notices of the Royal Astronomical Society》2006,373(2):623-631
H ii regions surrounding supermassive black holes (SMBHs) in an otherwise still neutral intergalactic medium (IGM) are likely to be the most easily detectable sources by future 21-cm experiments like LOFAR. We have made predictions for the size distribution of such H ii regions for several physically motivated models for BH growth at high redshift and compared this to the expected LOFAR sensitivity to these sources. The number of potentially detectable H ii regions does not only depend on the ionization state of the IGM and the decoupling of the spin temperature of the neutral hydrogen from the cosmic microwave background temperature, but is also strongly sensitive to the rate of growth of BHs at high redshift. If the SMBHs at redshift 6 were built up via continuous Eddington-limited accretion from low mass seed BHs at high redshift, then LOFAR is not expected to detect isolated QSO H ii regions at redshifts much larger than 6, and only if the IGM is still significantly neutral. If the high-redshift growth of BHs starts with massive seed BHs and is driven by short-lived accretion events following the merging of BH hosting galaxies then the detection of H ii regions surrounding SMBHs may extend to redshifts as large as 8–9 but is still very sensitive to the redshift to which the IGM remains significantly neutral. The most optimistic predictions are for a model where the SMBHs at z > 6 have grown slowly. H ii regions around SMBHs may then be detected to significantly larger redshifts. 相似文献
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V. D. Badalyan 《Astrophysics》2006,49(4):538-542
The angular dependence of the reflection coefficient is studied for electromagnetic waves passing through a one-dimensional
quasiperiodic dielectric layer. It is found that for certain types of quasiperiodic systems, omnidirectional reflection of
electromagnetic waves can occur.
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Translated from Astrofizika, Vol. 49, No. 4, pp. 631–636 (November 2006). 相似文献
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Sang-Hyeon Ahn 《Monthly notices of the Royal Astronomical Society》2005,358(4):1105-1115
We have analysed the meteor records in the chronicles that describe the era of the Song dynasty ( ad 960–1279). The data are complementary to the record-vacant 10th century of the Koryo dynasty ( ad 918–1392). The annual activity of sporadic meteors analysed shows a generic sinusoidal behaviour as in modern observations. In addition, we have also found that there are two prominent meteor showers, one in August and the other in November, appearing on the fluctuating sporadic meteors. The date of occurrence of the August shower indicates it to be the Perseids. By comparing the date of occurrence of the November shower with those of the Leonid showers of the Koryo dynasty, recent visual observations and the world-wide historical meteor storms, we conclude that the November shower is the Leonids. The regression rate of the Leonids is obtained to be days per century, which agrees with recent observations. 相似文献
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