Galaxy star formation in different environments

We use a semi-analytic model of galaxy formation to study signatures of large-scale modulations in the star formation (SF) activity in galaxies. In order to do this, we carefully define local and global estimators of the density around galaxies. The former are computed using a voronoi tessellation technique and the latter are parametrized by the normalized distance to haloes and voids, in terms of the virial and void radii, respectively. As a function of local density, galaxies show a strong modulation in their SF, a result that is in agreement with those from several authors. When taking subsamples of equal local density at different large-scale environments, we find relevant global effects whereby the fraction of red galaxies diminishes for galaxies in equal local density environments farther away from clusters and closer to voids. In general, the semi-analytic simulation is in good agreement with the available observational results, and offers the possibility to disentangle many of the processes responsible for the variation of galaxy properties with the environment; we find that the changes found in samples of galaxies with equal local environment but different distances to haloes or voids come from the variations in the underlying mass function of dark matter (DM) haloes. There is an additional possible effect coming from the host DM halo ages, indicating that halo assembly also plays a small but significant role (1.14σ) in shaping the properties of galaxies, and in particular, hints at a possible spatial correlation in halo/stellar mass ages. An interesting result comes from the analysis of the coherence of flows in different large-scale environments of fixed local densities; the neighbourhoods of massive haloes are characterized by lower coherences than control samples, except for galaxies in filament-like regions, which show highly coherent motions.     

B, V, I photometry of 20 dwarf irregular galaxies within 10 Mpc

CCD photometry is presented for 20 dIrr galaxies situated in the nearby complexes CenA/M83, and CVnI as well as in the general field of the Local Volume. We present integrated magnitudes of the galaxies in   B , V , I   bands and also surface brightness profiles to a median isophote  μ _B ∼ 28  mag arcsec⁻². The popular Sersic parametrization of surface brightness profiles generally does a poor job of simultaneously fitting the inner cores and outer exponential surface brightness fall-offs observed in many of our targets. The observed sample is a part of a general project to image about 500 nearby  ( D < 10 Mpc)  dwarf galaxies in multiple bands.     

Tidal evolution of discy dwarf galaxies in the Milky Way potential: the formation of dwarf spheroidals

We conduct high-resolution collisionless N -body simulations to investigate the tidal evolution of dwarf galaxies on an eccentric orbit in the Milky Way (MW) potential. The dwarfs originally consist of a low surface brightness stellar disc embedded in a cosmologically motivated dark matter halo. During 10 Gyr of dynamical evolution and after five pericentre passages, the dwarfs suffer substantial mass loss and their stellar component undergoes a major morphological transformation from a disc to a bar and finally to a spheroid. The bar is preserved for most of the time as the angular momentum is transferred outside the galaxy. A dwarf spheroidal (dSph) galaxy is formed via gradual shortening of the bar. This work thus provides a comprehensive quantitative explanation of a potentially crucial morphological transformation mechanism for dwarf galaxies that operates in groups as well as in clusters. We compare three cases with different initial inclinations of the disc and find that the evolution is fastest when the disc is coplanar with the orbit. Despite the strong tidal perturbations and mass loss, the dwarfs remain dark matter dominated. For most of the time, the one-dimensional stellar velocity dispersion, σ, follows the maximum circular velocity, V _max, and they are both good tracers of the bound mass. Specifically, we find that   M _bound∝ V ^3.5_max  and     in agreement with earlier studies based on pure dark matter simulations. The latter relation is based on directly measuring the stellar kinematics of the simulated dwarf, and may thus be reliably used to map the observed stellar velocity dispersions of dSphs to halo circular velocities when addressing the missing satellites problem.     

Fisher matrix decomposition for dark energy prediction

Within the context of constraining an expansion of the dark energy equation of state   w ( z ),  we show that the eigendecomposition of Fisher matrices is sensitive to both the maximum order of the expansion and the basis set choice. We investigate the Fisher matrix formalism in the case that a particular function is expanded in some basis set. As an example we show results for an all-sky weak lensing tomographic experiment. We show that the set of eigenfunctions is not unique and that the best constrained functions are only reproduced accurately at very higher order   N ≳ 100  , a top-hat basis set requires an even higher order. We show that the common approach used for finding the marginalized eigenfunction errors is sensitive to the choice of  non- w ( z )  parameters and priors. The eigendecomposition of Fisher matrices is a potentially useful tool that can be used to determine the predicted accuracy with which an experiment could constrain   w ( z )  . It also allows for the reconstruction of the redshift sensitivity of the experiment to changes in   w ( z )  . However, the technique is sensitive to both the order and the basis set choice. Publicly available code is available as part of icosmo at http://www.icosmo.org .     

安徽地区地震波衰减、场地响应及震源新参数的测定

根据安徽数字地震台网7个地震台的143条波形资料,研究了安徽地区的衰减模型和各台站的场地响应。采用三段几何衰减模型拟合,得到了安徽及邻近地区的几何衰减函数,得到安徽地区非弹性衰减Q值随频率f的关系为Q(f)=235.3×f0.616;7个台站的场地响应均无明显的放大效应,这与它们均处于岩石地基相符;并在本地区地震预测研究中尝试使用新参数,进行了初步的应用。     

海底浅表层不同土类静力触探参数与物理力学性质对比研究

海底土的物理、力学特性是海洋地质学、海洋土工学、海洋地质灾害等调查研究及海洋资源开发环境条件调查和评价等方面非常重要的资料,海底静力触探试验(CPT)是获取这方面资料的一种快速高效、成本低、测试精度高的原位测试方法。它可同时获取海底土锥尖阻力、侧摩阻力等方面的连续原位测试数据,这些数据与海底土取样样品测试分析资料及物探资料结合,可对海底土的工程特性等作比较全面的分析和评价。本文对采集的海底土样的静力触探参数与海底土样的物理力学指标进行相关分析,分粘性土和砂类土二类,建立了海底浅表层土的静力触探参数与物理力学指标之间的相关方程。利用相关方程可以通过静力触探的数据来推算土的物理力学指标,进而对海底土的工程情况作较全面的评价。     

Contribution of magnetic resonance sounding to aquifer characterization and recharge estimate in semiarid Niger

To improve the knowledge of the regionally important Continental Terminal 3 (CT3) aquifer in south-western Niger, fifteen magnetic resonance soundings (MRS) were carried out in December 2005 in the vicinity of wells and boreholes. The output MRS geophysical parameters, i.e. water content and decay constants versus depth, were compared to hydrogeological characteristics, i.e. water table depth, total porosity, specific yield and transmissivity estimated from direct measurements, pumping tests and transient groundwater modelling. The MRS-determined parameters were then used to estimate the rates of groundwater recharge.Contained in poorly consolidated Tertiary sandstones, the CT3 aquifer's water table has continuously risen by 4 m in total over the past four decades. Additionally, a significant portion of this increase has occurred in the past decade alone, with an annual rise now ranging between 0.1 and 0.3 m depending on the monitored well. Increase in groundwater recharge due to land clearance and deforestation explains this situation. According to previous estimations, the pre-clearing recharge ranged from 1 to 5 mm per year in 1950–60 s, while more recent recharge rates (1990s–2000s) range from 20 to 50 mm per year. These recharge values are directly affected by estimated aquifer specific yield value, while the spatial variation of rates of water table rise can be attributed to large scale hydrodynamic heterogeneities in the aquifer. However, few field measurements were available to confirm these assumptions.The main results of this study are: (1) The water table depth and aquifer transmissivity are estimated from MRS output parameters with an average accuracy of ± 10% and ± 9% respectively. (2) The MRS-determined water content is linked to both the total porosity and the specific yield of the aquifer, but no quantitative formulation can be proposed as yet. (3) Using the average MRS-determined water content over the investigated area, i.e. 13%, the groundwater recharge rates can be estimated to be ~ 2 mm per year in the 1950–1960s (pre-clearing period), and ~ 23 mm per year for the last decade. (4) The variations in specific yield and transmissivity cannot explain by themselves the spatial variability of the rise of the water table. (5) The ranges in transmissivity and water content obtained from MRS are more realistic than the groundwater modelling outputs. Therefore, MRS could be used to better constrain the aquifer parameters in groundwater modelling with a dense site network.Finally, this work illustrates how MRS can successfully improve characterisation and transient multi-year groundwater balance of commonly found sedimentary aquifers, particularly when integrated with well observations and pumping tests.     

边界补给量计算方法在宋桥井田的应用研究

利用宋桥井田奥灰群孔抽水试验资料,根据补（隔）水边界水位曲线的特征,采用半对数直线图解法,将井田F2-9断层定性为补给边界。为了解补给边界的补给量,选用边界补给量计算方法．计算出了边界补给量占孔流量的65％,从而较客观地确定了井田水文地质条件类型。