New clues to the evolution of dwarf early-type galaxies

Surface photometry of 18 Virgo cluster dwarf elliptical (dE) and dwarf lenticular (dS0) galaxies, made by Gavazzi et al. in the H band (1.65 μm) and in the B band (0.44 μm), shows that the ratio of the effective radii of these stellar systems in the B and H bands,   r _{e B} / r _{e H}   , ranges between 0.7 and 2.2. In particular, dwarf ellipticals and lenticulars with a red total colour index   B - H   (i.e. with  3.2< B - H <4)  have equal effective radii in these two passbands. By contrast, blue (i.e. with  2.5< B - H <3.1)  dEs and dS0s have B -band effective radii about 50 per cent larger than the H -band ones, on average. Consistently, strong negative gradients in   B - H   along the galactocentric radius are found to be associated with blue total colours. This trend is not found in a sample of 29 giant E and S0 galaxies of the Coma cluster with analogous data available in the literature. These early-type giants span a broad range in    r _{e B} / r _{e H}    (0.2–2.2)  , with a mean   r _{e B} / r _{e H} ∼1.1  , but a narrow range in (red) colour  (3.3< B - H <4.2)  . In these stellar systems, colour gradients are usually interpreted as arising either from age/metallicity gradients along the radial coordinate or from dust attenuation, whatever the total colour of the system is. Assuming each of these three distinct interpretations of the origin of colour gradients, we discuss the origin of the association of strong negative colour gradients with blue colours found in the early-type dwarfs under study, in relation with current scenarios of formation and evolution of dE and dS0 galaxies.     

The contribution of faint blue galaxies to the submillimetre counts and background

Observations in the submillimetre (submm) waveband have recently revealed a new population of luminous sources. These are proposed to lie at high redshift and to be optically faint because of their high intrinsic dust obscuration. The presence of dust has been previously invoked in optical galaxy count models which use the Bruzual & Charlot evolution models with an exponential τ =9 Gyr star formation rate (SFR) for spirals, and these fit the count data well from U to K . We now show that by using either a 1/ λ or Calzetti absorption law for the dust and re-distributing the evolved spiral galaxy ultraviolet (UV) radiation into the far-infrared (FIR), these models can account for all of the 'faint' ( 1 mJy) 850-μm galaxy counts, but fail to fit 'bright' ( 2 mJy) sources, indicating that another explanation for the submm counts may apply at brighter fluxes, e.g., quasi-stellar objects (QSOs) or ultraluminous infrared galaxies (ULIRGs). We find that the main contribution to the faint, submm number counts is in the redshift range 0.5< z <3, peaking at z ≈1.8. The above model, using either dust law, can also explain a significant proportion of the extragalactic background at 850 μm, as well as producing a reasonable fit to the bright 60-μm IRAS counts.     

Isolation,purification and characterization of the hydrogen evolution promoting factor of hydrogenase ofSpirulina platensis

A component (s-factor) with obvious promoting effect on hydrogen evolution of hydrogenase has been isolated and extracted from a cell-free preparation ofSpirulina platensis. The effect of the s-factor in the reaction system is similar to that of Na₂S₂O₄, but is coupled with light. The s-factor has the maximum absorption peak at 620 nm in the oxidized state, at 590 nm in the reduced state. The partially purified s-factor showed two bands by SDS-PAGE and is distinctly different from phycocyanin, which has no change of oxidized state and reduced state absorption spectra, and also has no promoting effect on hydrogenase ofSpirulina platensis under the light. The research supported by the NSFC.     

新疆尾亚韧性剪切带的基本特征及其意义

尾亚韧性剪切带形成于石炭纪晚期.根据其宏观变形构造、显微变形构造等变形特征,说明其经历了早期的推覆剪切和后期的右行推覆剪切两个主要演化阶段.对该区的构造演化及指导找矿增添了一点新的内容.     

Chemical evolution of the high redshift galaxies

We have tried to determine the rate of chemical evolution of high redshift galaxies from the observed redshift distribution of the heavy element absorption systems in the spectra of QSOs, taking into account the evolution in the intensity of the metagalactic UV ionizing radiation background, the radius and/or the co-moving number density of, and the fraction of mass in the form of gas in, the absorbers. The data for both the Lyman limit systems and the C IV systems have been fitted simultaneously. It seems that the abundance of carbon has possibly increased by about a factor of 5 to 20 from the cosmic time corresponding to the redshift ≃ 4 to 2. The data also suggest that either the radius or the co-moving number density of the galaxies increased with redshift up to z = 2.0 and decreased slowly thereafter. The total mass of the halo gas was higher in the past, almost equal to the entire mass of the galaxy at z = 4. The hydrogen column density distribution for Lyman limit systems predicted by the model is in agreement with the observed distribution.     

THE HOLOCENE SEDIMENTAL CHARACTERISTIC AND PALEOCLIMATIC EVOLUTION OF EBINUR LAKE，XINJIANG

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The chemical evolution of the Universe – I. High column density absorbers

We construct a simple, robust model of the chemical evolution of galaxies from high to low redshift, and apply it to published observations of damped Lyman α quasar absorption line systems (DLAs). The elementary model assumes quiescent star formation and isolated galaxies (no interactions, mergers or gas flows). We consider the influence of dust and chemical gradients in the galaxies, and hence explore the selection effects in quasar surveys. We fit individual DLA systems to predict some observable properties of the absorbing galaxies, and also indicate the expected redshift behaviour of chemical element ratios involving nucleosynthetic time delays.
Despite its simplicity, our 'monolithic collapse' model gives a good account of the distribution and evolution of the metallicity and column density of DLAs, and of the evolution of the global star formation rate and gas density below redshifts z ∼3. However, from the comparison of DLA observations with our model, it is clear that star formation rates at higher redshifts ( z >3) are enhanced. Galaxy interactions and mergers, and gas flows very probably play a major role.