Seasonal soil water dynamics in the jarrah forest,Western Australia. II: Results from a site with fine-textured soil profiles     

J. K. Ruprecht  N. J. Schofield 《水文研究》1990,4(3):259-267

Seasonal soil water dynamics were measured at a fine-textured, upslope site within the jarrah forest of southwest Western Australia and compared to the results from a coarse-textured hillslope transect. Gravity drainage dominated during winter and early spring. This reversed in early summer and an upward potential gradient was observed to 7 m depth. A shallow ephemeral saturation zone was observed above a clay pan at 1.5 m depth. This saturation zone persisted through late winter and early spring, contrasting with the short-lived saturation in the duricrust on the hillslope transect. The annual maximum to minimum unsaturated soil water storage was about 530 mm, 50 mm greater than the hillslope transect and higher than most values reported elsewhere in Australia. Significant soil water content changes following winter rain were generally restricted to 6 m but at one site occurred to 9 m. These depths were significantly less than the coarser-textured hillslope transect. Soil water drying rates averaged 5 mm day^?1 during extended dry periods compared to 3.5 mm day^?1 on the hillslope transect. The drying rate occurred uniformly through the profile until late summer when a significant decrease in the upper 3 m was observed.  相似文献   

The ages of quasar host galaxies     

L. A. Nolan  J. S. Dunlop  M. J. Kukula  D. H. Hughes  T. Boroson  R. Jimenez † 《Monthly notices of the Royal Astronomical Society》2001,323(2):308-330

We present the results of fitting deep off-nuclear optical spectra of radio-quiet quasars, radio-loud quasars and radio galaxies at z ≃0.2 with evolutionary synthesis models of galaxy evolution. Our aim was to determine the age of the dynamically dominant stellar populations in the host galaxies of these three classes of powerful active galactic nuclei (AGN). Some of our spectra display residual nuclear contamination at the shortest wavelengths, but the detailed quality of the fits longward of the 4000-Å break provides unequivocal proof, if further proof were needed, that quasars lie in massive galaxies with (at least at z ≃0.2) evolved stellar populations. By fitting a two-component model we have separated the very blue (starburst and/or AGN contamination) from the redder underlying spectral energy distribution, and find that the hosts of all three classes of AGN are dominated by old stars of age 8–14 Gyr. If the blue component is attributed to young stars, we find that, at most, 1 per cent of the visible baryonic mass of these galaxies is involved in star formation activity at the epoch of observation, at least over the region sampled by our spectroscopic observations. These results strongly support the conclusion reached by McLure et al. that the host galaxies of luminous quasars are massive ellipticals which have formed by the epoch of peak quasar activity at z ≃2.5.  相似文献   

The Sun, stellar-population models and the age estimation of high-redshift galaxies     

L. A. Nolan  J. S. Dunlop  R. Jimenez† 《Monthly notices of the Royal Astronomical Society》2001,323(2):385-390

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Supernovae in isolated galaxies, in pairs and in groups of galaxies     

H. Navasardyan  A.R. Petrosian  M. Turatto  E. Cappellaro  J. Boulesteix 《Monthly notices of the Royal Astronomical Society》2001,328(4):1181-1192

In order to investigate the influence of environment on supernova (SN) production, we have performed a statistical investigation of the SNe discovered in isolated galaxies, in pairs and in groups of galaxies. 22 SNe in 18 isolated galaxies, 48 SNe in 40 galaxy members of 37 pairs and 211 SNe in 170 galaxy members of 116 groups have been selected and studied.
We found that the radial distributions of core-collapse SNe in galaxies located in different environments are similar, and consistent with those reported by Bartunov, Makarova & Tsvetkov . SNe discovered in pairs do not favour a particular direction with respect to the companion galaxy. Also, the azimuthal distributions inside the host members of galaxy groups are consistent with being isotropics. The fact that SNe are more frequent in the brighter components of the pairs and groups is expected from the dependence of the SN rates on the galaxy luminosity.
There is an indication that the SN rate is higher in galaxy pairs compared with that in groups. This can be related to the enhanced star formation rate in strongly interacting systems.
It is concluded that, with the possible exception of strongly interacting systems, the parent galaxy environment has no direct influence on SN production.  相似文献   

A comparison of stellar populations in galaxy spheroids across a wide range of Hubble types     

R. N. Proctor  A. E. Sansom 《Monthly notices of the Royal Astronomical Society》2002,333(3):517-543

We present line-strengths and kinematics from the central regions of 32 galaxies with Hubble types ranging from E to Sbc. Spectral indices, based on the Lick system, are measured in the optical and near-infrared (NIR). The 24 indices measured, in conjunction with models of the effects of varying abundance ratios, permit the breaking of age/metallicity degeneracy, and allow estimation of enhancements in specific light elements (particularly C and Mg). The large range of Hubble types observed allows direct comparison of line-strengths in the centres of early-type galaxies (E and S0) with those in spiral bulges, free from systematic differences that have plagued comparisons of results from different studies. Our sample includes field and Virgo cluster galaxies. For early-type galaxies our data are consistent with previously reported trends of Mg₂ and Mgb with velocity dispersion. In spiral bulges we find trends in all indices with velocity dispersion. We estimate luminosity-weighted ages, metallicities and heavy-element abundance ratios (enhancements) from optical indices. These show that bulges are less enhanced in light ( α -capture) elements and have lower average age than early-type galaxies. Trends involving age and metallicity also differ sharply between early and late types. An anticorrelation exists between age and metallicity in early types, while, in bulges, metallicity is correlated with velocity dispersion. We consider the implications of these findings for models of the formation of these galaxies. We find that primordial collapse models of galaxy formation are ruled out by our observations, while several predictions of hierarchical clustering (merger) models are confirmed.  相似文献   

The field of NGC 6397 as a test for Galactic models     

V. Castellani  S. Degl'Innocenti  S. Petroni  G. Piotto 《Monthly notices of the Royal Astronomical Society》2001,324(1):167-179

Taking advantage of recent Hubble Space Telescope ( HST ) data for field stars in the region of the Galactic globular cluster NGC 6397, we tested the predictions of several Galactic models with star counts reaching a largely unexplored range of magnitudes, down to V ∼26.5. After updating the input stellar ( V − I ) colours, we found that the two-component Bahcall–Soneira (B&S) model can be put into satisfactory agreement with observations for suitable choices of disc/spheroid luminosity functions (LFs). However, if one assumes the disc LF of Gould, Bahcall and Flynn together with the spheroid LF of Gould, Flynn and Bahcall, there is no way to reconcile the predicted and observed V -magnitude distribution. We also analysed the agreement between observed and predicted magnitude and colour distributions for two selected models with a thick disc component. Even in this case there are suitable combinations of model parameters and faint-magnitude LFs that can give a reasonable agreement with observational star counts in both magnitude and colour. However, the above-quoted combination of Gould et al. LFs again gives predictions in clear disagreement with observations.  相似文献   

基于信息量模型的中国滑坡灾害风险区划研究   总被引：33，自引：2，他引：31  

朱良峰  吴信才  殷坤龙  刘修国 《地球科学与环境学报》2004,26(3):52-56

基于信息论发展起来的信息量模型是进行区域滑坡灾害风险评估的一种有效方法。GIS技术为滑坡灾害在不同模型条件下的风险评估提供了有效地技术支持。经过研究，开发出了基于MapGIS软件平台的滑坡灾害风险分析系统。在该系统支持下．采用信息量模型对中国范围内的滑坡灾害进行危险性分析。进而进行区域社会经济易损性分析。并在此基础上进行最终的滑坡灾害风险评估。  相似文献   

A different approach for the estimation of Galactic model parameters     

S. Karaali  S. Bilir  E. Hamzao&#;lu 《Monthly notices of the Royal Astronomical Society》2004,355(1):307-320

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Synthetic stellar populations: single stellar populations, stellar interior models and primordial protogalaxies     

Raul Jimenez  James MacDonald  James S. Dunlop  Paolo Padoan  John A. Peacock 《Monthly notices of the Royal Astronomical Society》2004,349(1):240-254

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Displacement of X-ray sources from star clusters in starburst galaxies   总被引：1，自引：0，他引：1  

P. Kaaret  A. Alonso-Herrero  J. S. Gallagher  III    G. Fabbiano  A. Zezas  M. J. Rieke 《Monthly notices of the Royal Astronomical Society》2004,348(2):L28-L32

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