Contrasting the chemical evolution of the Milky Way and Andromeda     

Agostino Renda  Daisuke Kawata  Yeshe Fenner  Brad K. Gibson 《Monthly notices of the Royal Astronomical Society》2005,356(3):1071-1078

The chemical evolution history of a galaxy hides clues about how it formed and has been changing through time. We have studied the chemical evolution history of the Milky Way (MW) and Andromeda (M31) to find which are common features in the chemical evolution of disc galaxies as well as which are galaxy-dependent. We use a semi-analytic multizone chemical evolution model. Such models have succeeded in explaining the mean trends of the observed chemical properties in these two Local Group spiral galaxies with similar mass and morphology. Our results suggest that while the evolution of the MW and M31 shares general similarities, differences in the formation history are required to explain the observations in detail. In particular, we found that the observed higher metallicity in the M31 halo can be explained by either (i) a higher halo star formation efficiency (SFE), or (ii) a larger reservoir of infalling halo gas with a longer halo formation phase. These two different pictures would lead to (i) a higher [O/Fe] at low metallicities, or (ii) younger stellar populations in the M31 halo, respectively. Both pictures result in a more massive stellar halo in M31, which suggests a possible correlation between the halo metallicity and its stellar mass.  相似文献   

基于遥感技术对黄河口水色与岸线季相变化特征研究     

马安青  胡泓  袁道伟  胡婷 《中国海洋大学学报(自然科学版)》2008,38(1):151-156

使用Landsat-5 TM 2004年11月24日与2005年5月13日黄河口遥感影像,配合准同期外业实测资料,进行黄河口水体水色物质叶绿素a与悬浮泥沙的动态反演与河口岸线解译.研究表明由于秋末与春初黄河上游来水物质含量的差异,上述悬浮指标值存在显著的季相差异.根据样值与光谱特征建立的反演模型得出的反演值与实测值有平均在0.85以上的相关关系,具有很好的反演效果.岸线解译成果表明,黄河口岸线演变迅速,在河流平枯水量时期仍然具有较强的变化,岸线推进尤以新河口附近显著.这表明,使用遥感手段是进行河口生态环境质量监测的有效手段,是进行岸线动态变化研究的一种基本技术支撑手段.  相似文献   

定水头注水引起的含水层水平运动和应变   总被引：2，自引：2，他引：0  

王庆良  冉兴龙 《大地测量与地球动力学》2001,21(4):26-32

基于含水层固体颗粒与孔隙水不可压缩的假设 ,本文导出了单井注水情况下泰斯承压含水层水平运动速度与水头之间的基本关系式。然后利用注水井壁处的应力、应变边界条件 ,进一步导出了单井定水头注水引起的泰斯承压含水层水平运动速度、位移和应变解析表达式。该水平位移与应变由两部分组成 :一部分为由注水压力本身引起的经典弹性力学解项 ,它仅随半径而变化 ,与注水时间无关 ;另一部分为由地下水头变化引起的水动力学位移和应变解项。其中 ,含水层水动力学水平位移随时间加长呈指数增长特征 ,水动力学径向应变则表现为近井处拉张、远井处挤压的分区特征 ,且近井拉张区随时间加长逐渐向外扩展。单井注水含水层水动力学水平位移、应变解的导出 ,完善和发展了单孔内压经典弹性平面力学问题解  相似文献   

风沙路基施工技术初探     

周发贵 《地球科学与环境学报》2001,23(1):63-65

路基施工中保证路基填筑密实度，通常沙土路基采用水夯；普通路基采用振动碾、羊角碾等重型机具振密夯实。但在缺电、缺水，高气温、大风沙的沙漠气候等恶劣的施工条件下，风沙路基的施工如何保证路基填筑的密实度和施工机械在风沙路基上作业而不陷车的问题，就目前没有合适的经验可借鉴，也没有规范可参考。因此把在包西线神木北至延安北段的铁路工程建设中风沙路基施工所取得的经验和施工技术作一介绍。  相似文献   

THE CHARACTERISTIC OF MARINE ENVIRONMENT IN LINGDINGYANG ESTUARY     

CHEN Bing-lu  ZHANG Yun-ni  CHEN Xin-geng  WANG Zhi-gang  YANG Guang-xing 《中国地理科学(英文版)》2001,11(2):155-162

1 HYDROLOGIC FEATURES Lingdingyang Estuary, located at the middle south of Guangdong Province, is a bell-shaped estuary with a north-south direction. Its area is about 2100km2. The north of Qi′ao Island and Inner-Lingding Island, and the south of Humen are grouped as Neilingdingyang Estuary, having an area of 1041km2. Affected by topography, runoff and tide, its dynamic condition is very complicated. Different water areas have different hydrologic features. The topography under …  相似文献   

Mid-infrared, Hα and radio continuum images of an unusual H ii region, G308.70 + 0.60     

Martin Cohen  Anne J. Green  Quentin A. Parker  Stacy Mader  Russell D. Cannon 《Monthly notices of the Royal Astronomical Society》2002,336(3):736-746

  相似文献   

On the Line Formation in Stellar Magnetized Atmospheres     

Zhong-Quan Qu  Xiao-Yu Zhang  Zhi Xu 《中国天文和天体物理学报》2001,1(2):161-175

1 INTRODUCTIONIn the previous paper (on et al. 1999, hereafter Paper I), we investigated the wavelength-dependence of four colltribution functions (CFs) derived from dmerent formal solutions andreferring to different emergellt quantities in the unpolarized case. Because one cannot generallyassign a single formation region to the whole line band in a real stellar atmosphere, e.g., the solaratmosphere, instead, the line formation region can be defined as the layers deviating farthestfrom t…  相似文献   

The pairwise velocity dispersion of galaxies: effects of non-radial motions     

A. Del Popolo 《Monthly notices of the Royal Astronomical Society》2001,326(2):667-674

I discuss the effect of non-radial motions on the small-scale peculiar pairwise velocity dispersions (PVD) of galaxies in a cold dark matter (CDM) model and calculate the PVD for the SCDM model by means of the refined cosmic virial theorem (CVT), taking account of non-radial motions by means of the Del Popolo & Gambera model. I compare the results of the present model with the data from Davis & Peebles, the IRAS value at 1  h ⁻¹ Mpc of Fisher et al. and Marzke et al. I show that while the SCDM model disagrees with the observed values, as pointed out by several authors, taking account of non-radial motions produces smaller values for the PVD. At r ≤1  h ⁻¹ Mpc the result is in agreement with Bartlett & Blanchard. In the light of this last paper, the result may be also read as a strong dependence of the CVT prediction on the model chosen to describe the mass distribution around galaxies, suggesting that the CVT cannot be taken as a direct evidence for a low-density Universe. Similarly to what is shown by Del Popolo & Gambera and Del Popolo et al., the agreement of our model to the observational data is because of a scale-dependent bias induced by the presence of non-radial motions. As the assumptions on which CVT is based have been questioned by several authors, I also calculated the PVD using the redshift distortion in the redshift-space correlation function, ξ _z( r _p, π), and compared it with the PVD measured from the Las Campanas Redshift Survey by Jing et al. The result confirms that non-radial motions influence the PVD making them agree better with the observed data.  相似文献   

Double starbursts triggered by mergers in hierarchical clustering scenarios     

P. B. Tissera  R. Domínguez-Tenreiro  C. Scannapieco  A. Sáiz 《Monthly notices of the Royal Astronomical Society》2002,333(2):327-338

We use cosmological smooth particle hydrodynamical (SPH) simulations to study the effects of mergers in the star formation history of galactic objects in hierarchical clustering scenarios. We find that during some merger events, gaseous discs can experience two starbursts: the first one during the orbital decay phase, owing to gas inflows driven as the satellite approaches, and the second one when the two baryonic clumps collide. A trend for these first induced starbursts to be more efficient at transforming the gas into stars is also found. We detect that systems that do not experience early gas inflows have well-formed stellar bulges and more concentrated potential wells, which seem to be responsible for preventing further gas inward transport triggered by tidal forces. The potential wells concentrate owing to the accumulation of baryons in the central regions and of dark matter as the result of the pulling in by baryons. The coupled evolution of the dark matter and baryons would lead to an evolutionary sequence during which systems with shallower total potential wells suffer early gas inflows during the orbital decay phase that help to feed their central mass concentration, pulling in dark matter and contributing to build up more stable systems. Within this scenario, starbursts triggered by early gas inflows are more likely to occur at early stages of evolution of the systems and to be an important contributor to the formation of stellar bulges. Our results constitute the first proof that bulges can form as the product of collapse, collisions and secular evolution in a cosmological framework, and they are consistent with a rejuvenation of the stellar population in bulges at intermediate z with, at least, 50 per cent of the stars (in SCDM) being formed at high z .  相似文献   

Evolution of the luminosity function and colours of galaxies in a Λ cold dark matter universe     

K. Nagamine †  M. Fukugita  R. Cen  J.P. Ostriker 《Monthly notices of the Royal Astronomical Society》2001,327(1):L10-L14

The luminosity function of galaxies is derived from a cosmological hydrodynamic simulation of a Λ cold dark matter universe with the aid of a stellar population synthesis model. At     , the resulting B -band luminosity function has a flat faint-end slope of     with the characteristic luminosity and the normalization in fair agreement with observations, while the dark matter halo mass function is steep with a slope of     . The colour distribution of galaxies also agrees well with local observations. We also discuss the evolution of the luminosity function, and the colour distribution of galaxies from     to 5. A large evolution of the characteristic mass in the stellar mass function as a result of number evolution is compensated by luminosity evolution; the characteristic luminosity increases only by 0.8 mag from     to 2, and then declines towards higher redshift, while the B -band luminosity density continues to increase from     to 5 (but only slowly at     .  相似文献