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P. C. Hewett S. J. Warren S. K. Leggett S. T. Hodgkin 《Monthly notices of the Royal Astronomical Society》2006,367(2):454-468
We present a statistical study of a very large sample of H ii galaxies taken from the literature. We focus on the differences in several properties between galaxies that show the auroral line [O iii ]λ4363 and those that do not present this feature in their spectra. It turns out that objects without this auroral line are more luminous, are more metal-rich and present a lower ionization degree. The underlying population is found to be much more important for objects without the [O iii ]λ4363 line, and the effective temperature of the ionizing star clusters of galaxies not showing the auroral line is probably lower. We also study the subsample of H ii galaxies whose properties most closely resemble the properties of the intermediate-redshift population of luminous compact blue galaxies (LCBGs). The objects from this subsample are more similar to the objects not showing the [O iii ]λ4363 line. It might therefore be expected that the intermediate- redshift population of LCBGs is powered by very massive, yet somewhat aged, star clusters. The oxygen abundance of LCBGs would be greater than the average oxygen abundance of local H ii galaxies. 相似文献
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Randall B. Wayth Stephen J. Warren Geraint F. Lewis Paul C. Hewett 《Monthly notices of the Royal Astronomical Society》2005,360(4):1333-1344
We perform a detailed analysis of the optical gravitational lens ER 0047–2808 imaged with the Wide Field Planetary Camera 2 on the Hubble Space Telescope . Using software specifically designed for the analysis of resolved gravitational lens systems, we focus on how the image alone can constrain the mass distribution in the lens galaxy. We find that the data are of sufficient quality to strongly constrain the lens model with no a priori assumptions about the source. Using a variety of mass models, we find statistically acceptable results for elliptical isothermal-like models with an Einstein radius of 1.17 arcsec. An elliptical power-law model (Σ∝ R −β ) for the surface mass density favours a slope slightly steeper than isothermal with β= 1.08 ± 0.03 . Other models including a constant mass-to-light ratio (M/L), pure Navarro, Frenk & White halo and (surprisingly) an isothermal sphere with external shear are ruled out by the data. We find the galaxy light profile can only be fit with a Sérsic plus point-source model. The resulting total M/L B contained within the images is 4.7 h 65 ± 0.3 . In addition, we find the luminous matter is aligned with the total mass distribution within a few degrees. This is the first time a resolved optical gravitational lens image has been quantitatively reproduced using a non-parametric source.
The source, reconstructed by the software, is revealed to have two bright regions, with an unresolved component inside the caustic and a resolved component straddling a fold caustic. The angular size of the entire source is ∼0.1 arcsec and its (unlensed) Lyα flux is 3 × 10−17 erg s−1 cm−2 . 相似文献
The source, reconstructed by the software, is revealed to have two bright regions, with an unresolved component inside the caustic and a resolved component straddling a fold caustic. The angular size of the entire source is ∼0.1 arcsec and its (unlensed) Lyα flux is 3 × 10
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J.P. Willis † P.C. Hewett S.J. Warren 《Monthly notices of the Royal Astronomical Society》2001,325(3):1002-1016
We have compiled a sample of ∼ 9600 bright, i ≤18.95 , red, b J − r >2 , candidate galaxies in an area of 220 deg2 . These are luminous, L > L * , field early-type galaxies with redshifts 0.3≲ z ≲0.6 . We present a redshift catalogue of a subsample of 581 targets. The galaxies were selected according to their broad-band b J ri colours from United Kingdom Schmidt Telescope plates, and have a surface density on the sky of only ∼ 50 deg−2 . Such luminous field galaxies are virtually absent from published redshift surveys and the catalogue provides a large sample of the most luminous normal galaxies, at cosmological distances. The statistical properties of the galaxy spectra, including absorption-line and emission-line measures, are presented and a composite spectrum constructed. The nature of the sample, combined with the relatively bright apparent magnitudes, makes the galaxies suitable targets for several key investigations in galaxy evolution and cosmology. 相似文献
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Isaac G. Roseboom Kevin A. Pimbblet Michael J. Drinkwater Russell D. Cannon Roberto De Propris Alastair C. Edge Daniel J. Eisenstein Robert C. Nichol Ian Smail David A. Wake Joss Bland-Hawthorn Terry J. Bridges Daniel Carson Matthew Colless Warrick J. Couch Scott M. Croom Simon P. Driver Paul C. Hewett Jon Loveday Nic Ross Donald P. Schneider Tom Shanks Robert G. Sharp Peter Weilbacher 《Monthly notices of the Royal Astronomical Society》2006,373(1):349-360
We present a detailed investigation into the recent star formation histories of 5697 luminous red galaxies (LRGs) based on the Hδ (4101 Å), and [O ii ] (3727 Å) lines and the D4000 index. LRGs are luminous ( L > 3 L *) galaxies which have been selected to have photometric properties consistent with an old, passively evolving stellar population. For this study, we utilize LRGs from the recently completed 2dF-SDSS LRG and QSO Survey (2SLAQ). Equivalent widths of the Hδ and [O ii ] lines are measured and used to define three spectral types, those with only strong Hδ absorption (k+a), those with strong [O ii ] in emission (em) and those with both (em+a). All other LRGs are considered to have passive star formation histories. The vast majority of LRGs are found to be passive (∼80 per cent); however, significant numbers of k+a (2.7 per cent), em+a (1.2 per cent) and em LRGs (8.6 per cent) are identified. An investigation into the redshift dependence of the fractions is also performed. A sample of SDSS MAIN galaxies with colours and luminosities consistent with the 2SLAQ LRGs is selected to provide a low-redshift comparison. While the em and em+a fractions are consistent with the low-redshift SDSS sample, the fraction of k+a LRGs is found to increase significantly with redshift. This result is interpreted as an indication of an increasing amount of recent star formation activity in LRGs with redshift. By considering the expected lifetime of the k+a phase, the number of LRGs which will undergo a k+a phase can be estimated. A crude comparison of this estimate with the predictions from semi-analytic models of galaxy formation shows that the predicted level of k+a and em+a activities is not sufficient to reconcile the predicted mass growth for massive early types in a hierarchical merging scenario. 相似文献
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Fast 3D Reservoir Simulation and Scale Up Using Streamtubes 总被引：1，自引：0，他引：1
This paper presents an implementation of a semianalytical method for oil recovery calculation in heterogeneous reservoirs that is both fast and accurate. The method defines streamline paths based on a conventional single-phase incompressible flow calculation. By calculating the time-of-flight for a particle along a streamline and assigning a volumetric flux to each streamline, the cumulative pore volume of a streamtube containing the streamline can be calculated. Subsequently, the streamtube geometries are kept constant and the effects of the time varying mobility distribution in two-phase flow are accounted for by varying the flow rate in each streamtube, based on fluid resistance changes along the streamtube. Oil recovery calculations are then done based on the 1D analytical Buckley–Leverett solution. This concept makes the method extremely fast and easy to implement, making it ideal to simulate large reservoirs generated by geostatiscal methods. The simulation results of a 3D heterogeneous reservoir are presented and compared with those of other simulators. The results shows that the new simulator is much faster than a traditional finite difference simulator, while having the same accuracy. The method also naturally handles the upscaling of absolute and relative permeability. We make use of these upscaling abilities to generate a coarse curvilinear grid that can be used in conventional simulators with a great advantage over conventional upscaled Cartesian grids. This paper also shows an upscaling example using this technique. 相似文献
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D. M. Bramich S. Vidrih L. Wyrzykowski J. A. Munn H. Lin N. W. Evans M. C. Smith V. Belokurov G. Gilmore D. B. Zucker P. C. Hewett L. L. Watkins D. C. Faria M. Fellhauer G. Miknaitis D. Bizyaev &#;. Ivezi&#; D. P. Schneider S. A. Snedden E. Malanushenko V. Malanushenko K. Pan 《Monthly notices of the Royal Astronomical Society》2008,386(2):887-902