排序方式： 共有23条查询结果，搜索用时 15 毫秒
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Malcolm Longair 《Experimental Astronomy》2009,25(1-3):241-259
The wide diversity of routes to astronomical, astrophysical and cosmological discovery is discussed through a number of historical case studies. Prime ingredients for success include new technology, precision observation, extensive databases, capitalising upon discoveries in cognate disciplines, imagination and luck. Being in the right place at the right time is a huge advantage. The changing perspectives on the essential tools for tackling frontier problems and astronomical advance are discussed. 相似文献
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T. G. Arshakian M. S. Longair 《Monthly notices of the Royal Astronomical Society》2000,311(4):846-860
There is substantial observational evidence against the symmetric relativistic model of FR II radio sources. An asymmetric relativistic model is proposed which takes account of both relativistic effects and intrinsic/environmental asymmetries to explain the structural asymmetries of their radio lobes. A key parameter of the model is the jet-side of the double sources, which is estimated for 80 per cent of the FR II sources in the 3CRR complete sample. Statistical analyses of the properties of these sources show that the asymmetric model is in agreement with a wide range of observational data, and that the relativistic and intrinsic asymmetry effects are of comparable importance. Intrinsic/environmental asymmetry effects are more important at high radio luminosities and small physical scales. The mean translational speed of the lobes is found to be consistent with the speeds found from spectral ageing arguments. According to a Gaussian model, the standard deviation of the distribution of v lobe is σ v l =0.04 c . The results are in agreement with an orientation-based unification scheme in which the critical angle separating the radio galaxies from quasars is about 45°. 相似文献
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J. A. Peacock M. Rowan-Robinson A. W. Blain J. S. Dunlop A. Efstathiou D. H. Hughes T. Jenness R. J. Ivison A. Lawrence M. S. Longair R. G. Mann S. J. Oliver S. Serjeant 《Monthly notices of the Royal Astronomical Society》2000,318(2):535-546
We use an 850-μm SCUBA map of the Hubble Deep Field (HDF) to study the dust properties of optically-selected starburst galaxies at high redshift. The optical/infrared (IR) data in the HDF allow a photometric redshift to be estimated for each galaxy, together with an estimate of the visible star-formation rate. The 850-μm flux density of each source provides the complementary information: the amount of hidden, dust-enshrouded star formation activity. Although the 850-μm map does not allow detection of the majority of individual sources, we show that the galaxies with the highest UV star-formation rates are detected statistically, with a flux density of about S 850 =0.2 mJy for an apparent UV star-formation rate of 1 h −2 M⊙ yr−1 . This level of submillimetre output indicates that the total star-forming activity is on average a factor of approximately 6 times larger than the rate inferred from the UV output of these galaxies. The general population of optical starbursts is then predicted to contribute at least 25 per cent of the 850-μm background. We carry out a power-spectrum analysis of the map, which yields some evidence for angular clustering of the background source population, but at a level lower than that seen in Lyman-break galaxies. Together with other lines of argument, particularly from the NICMOS HDF data, this suggests that the 850-μm background originates over an extremely wide range of redshifts – perhaps 1≲ z ≲6. 相似文献
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M. J.Fox A.Efstathiou M.Rowan-Robinson J. S.Dunlop S.Scott S.Serjeant R. G.Mann S.Oliver R. J.Ivison A.Blain O.Almaini D.Hughes C. J.Willott M.Longair A.Lawrence J. A.Peacock 《Monthly notices of the Royal Astronomical Society》2002,331(4):839-852
We present the results of a multiwavelength study of the 19 most significant submillimetre (submm) sources detected in the SCUBA 8-mJy survey. As described in Scott et al. , this survey covers ≃260 arcmin2 using the submillimetre camera SCUBA, to a limiting source detection limit S 850 μm ≃8 mJy . One advantage of this relatively bright flux-density limit is that accurate astrometric positions are potentially achievable for every source using existing radio and/or millimetre-wave interferometers. However, an associated advantage is that spectral energy distribution (SED) based redshift constraints should be more powerful than in fainter submm surveys. Here we therefore exploit the parallel SCUBA 450-μm data, in combination with existing radio and Infrared Space Observatory ( ISO ) data at longer and shorter wavelengths to set constraints on the redshift of each source. We also analyse new and existing optical and near-infrared imaging of our SCUBA survey fields to select potential identifications consistent with these constraints. Our derived SED-based redshift constraints, and the lack of statistically significant associations with even moderately bright galaxies allow us to conclude that all 19 sources lie at z >1 , and at least half of them apparently lie at z >2 . 相似文献
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Bojan Nikolic Paul Alexander Garret Cotter Malcolm Longair Marcel Clemens 《Astrophysics and Space Science》2003,284(2):573-576
We present preliminary results of recent spatially resolved mid infrared (Mid-IR) spectroscopy with the MICHELLE instrument
on UKIRT of NGC 7469, observed as part of a larger programme to study a sample of starburst and AGN in the Mid-IR.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献