Chemical Enrichment of the Intra-Cluster Medium     

SofÍa A. Cora  Simon D.M. White 《Astrophysics and Space Science》2003,284(2):425-428

We investigate the metal enrichment of the intra-cluster medium by using a method that combines N-Body simulations and a semi-analytic model (SAM) of galaxy formation. The cluster of galaxies is simulated in a flat, low density universe, with a numerical resolution that allows the detection of substructures in the dark matter background of the cluster. The phenomenological approach used to model the physical processes involved in the galaxy formation and metal production is applied to the substructures found in the dark matter halos detected at different redshifts. Details of the chemical implementation in the SAM and first results related to the mean properties of the baryonic matter components are presented. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Stellar masses and star formation histories for 10⁵ galaxies from the Sloan Digital Sky Survey     

Guinevere Kauffmann  Timothy M. Heckman  Simon D. M. White  Stéphane Charlot  Christy Tremonti  Jarle Brinchmann  Gustavo Bruzual  Eric W. Peng  Mark Seibert  Mariangela Bernardi  Michael Blanton  Jon Brinkmann  Francisco Castander  Istvan Csábai  Masataka Fukugita  Zeljko Ivezic  Jeffrey A. Munn  Robert C. Nichol  Nikhil Padmanabhan  Aniruddha R. Thakar  David H. Weinberg  Donald York 《Monthly notices of the Royal Astronomical Society》2003,341(1):33-53

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The host galaxies of active galactic nuclei   总被引：2，自引：0，他引：2  

Guinevere Kauffmann  Timothy M. Heckman  Christy Tremonti  Jarle Brinchmann  Stéphane Charlot  Simon D. M. White  Susan E. Ridgway  Jon Brinkmann  Masataka Fukugita  Patrick B. Hall  &#;eljko Ivezi&#;  Gordon T. Richards  Donald P. Schneider 《Monthly notices of the Royal Astronomical Society》2003,346(4):1055-1077

We examine the properties of the host galaxies of 22 623 narrow-line active galactic nuclei (AGN) with  0.02 < z < 0.3  selected from a complete sample of 122 808 galaxies from the Sloan Digital Sky Survey. We focus on the luminosity of the [O  iii ]λ5007 emission line as a tracer of the strength of activity in the nucleus. We study how AGN host properties compare with those of normal galaxies and how they depend on L [O  iii ]. We find that AGN of all luminosities reside almost exclusively in massive galaxies and have distributions of sizes, stellar surface mass densities and concentrations that are similar to those of ordinary early-type galaxies in our sample. The host galaxies of low-luminosity AGN have stellar populations similar to normal early types. The hosts of high-luminosity AGN have much younger mean stellar ages. The young stars are not preferentially located near the nucleus of the galaxy, but are spread out over scales of at least several kiloparsecs. A significant fraction of high-luminosity AGN have strong Hδ absorption-line equivalent widths, indicating that they experienced a burst of star formation in the recent past. We have also examined the stellar populations of the host galaxies of a sample of broad-line AGN. We conclude that there is no significant difference in stellar content between type 2 Seyfert hosts and quasars (QSOs) with the same [O  iii ] luminosity and redshift. This establishes that a young stellar population is a general property of AGN with high [O  iii ] luminosities.  相似文献   

Star cluster ecology – V. Dissection of an open star cluster: spectroscopy     

Simon F. Portegies Zwart †  Piet Hut  Stephen L. W. McMillan  Junichiro Makino 《Monthly notices of the Royal Astronomical Society》2004,351(2):473-486

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Swimming with…Devonian fish     

Lance B. Morrissey  Philippe Janvier  Simon J. Braddy  John P. Bennett  Susan B. Marriott  Peter R. Tarrant 《Geology Today》2006,22(2):66-67

Armoured jawless fish, or 'ostracoderms', lived 450–360 million years ago, and display unusual morphologies, unlike any modern fish group. Since they left no living descendants, their mode of swimming has, until recently, remained speculative, although this is a crucial question as the first true pectoral fins evolved within the 'ostracoderms'. The discovery of the oldest-known fish trails, from the Early Devonian (400 million year old) 'Lower Old Red Sandstone' of south-east Wales offers new insights into the swimming behaviour of these early fish, notably the osteostracan 'ostracoderms' (or cephalaspids), whose horseshoe-shaped head and paddle-shaped pectoral fins have remained a functional riddle.  相似文献   

Ultraviolet solar irradiance measurement from 200 to 358 nm during spacelab 1 mission     

D. Labs  H. Neckel  P. C. Simon  G. Thuillier 《Solar physics》1987,107(2):203-219

The paper presents the results obtained from the UV-spectrometer of the Solar Spectrum Experiment during the Spacelab 1 mission in December 1983. The irradiance data concern 492 passbands, which are located between 200 and 358 nm at almost equidistant wavelengths separated by about 0.3 nm. The passbands have a well-defined, bell-shaped profile with a full width at half maximum of about 1.3 nm. The data, which have an error budget between 4 and 5%, agree closely with the spectral distributions observed by Heath (1980) and Mentall et al. (1981) and confirm that the solar irradiance and the fluxes of Sun-like stars show about the same spectral distribution down to at least 240 nm.  相似文献   

Late Palaeozoic hydrocarbon migration through the Clair field, West of Shetland, UK Atlantic margin     

Darren F. Mark  Paul F. Green  John Parnell  Simon P. Kelley  Martin R. Lee  Sarah C. Sherlock 《Geochimica et cosmochimica acta》2008,72(10):2510-2533

Geochemical analysis of bitumen- and hydrocarbon-bearing fluid inclusions from the Devonian-Carboniferous Clair field indicates that the reservoirs contain a mixture of oils from different marine and lacustrine sources. Reconstruction of the Clair field oil-charge history using fluid inclusion petrography show that oil-charging occurred at times of K-feldspar, quartz and calcite cementation. Temperature–composition–time data yielded from the integration of fluid inclusion microthermometry with high-resolution Ar–Ar dating, date hydrocarbon-bearing K-feldspar overgrowths at 247 ± 3.3 Ma. These data show that in order for oil to be trapped within primary fluid inclusions in K-feldspar overgrowths, hydrocarbon migration throughout the UK Atlantic margin must have been taking place during the Late Palaeozoic and as such, current industry oil-play models based solely on oil charging from Jurassic-Cretaceous marine sources are clearly incomplete and need revision. Apatite fission track analysis and vitrinite reflectance data were used to reconstruct thermal burial histories and assess potential oil generation from Middle Devonian lacustrine source rocks. Thermal history data from wells along The Rona Ridge adjacent to the Clair field show that the Palaeozoic section was heated to greater than 100 °C at some time between 270 and 230 Ma, confirming that Devonian source rocks were mature and expelling oil during the Late Palaeozoic at the time that authigenic K-feldspar overgrowths were growing in the Clair field.  相似文献   

Controls of δS and δO in dissolved sulphate: Learning from a detailed survey in the Llobregat River (Spain)     

Neus Otero  Albert Soler  Àngels Canals 《Applied Geochemistry》2008

The S and O isotopic composition of dissolved SO₄, used as a tracer for SO₄ sources, was applied to the water of the Llobregat River system (NE Spain). The survey was carried out at 30 sites where surface water was sampled on a monthly basis over a period of 2a. The concentration of dissolved SO₄ varied from 20 to 1575 mg L⁻¹. Sulphur isotopic compositions clustered in two populations: one – 93% of the samples – had positive values with a mode of +9‰; the other had negative values and a mode of −5‰. Data for δ¹⁸O_SO4 showed a mean value of +11‰, with no bi-modal distribution, though lower values of δ¹⁸O corresponded to samples with negative δ³⁴S. These values can not be explained solely by the contribution of bedrock SO₄ sources: that is, sulphide oxidation and the weathering of outcrops of sulphates, though numerous chemical sediments exist in the basin. Even in a river with a high concentration of natural sources of dissolved SO₄, such as the Llobregat River, the δ³⁴S values suggest that dissolved SO₄ is controlled by a complex mix of both natural and anthropogenic sources. The main anthropogenic sources in this basin are fertilizers, sewage, potash mine effluent and power plant emissions. Detailed river water sampling, together with the chemical and isotopic characterisation of the main anthropogenic inputs, allowed determination of the influence of redox processes, as well as identification of the contribution of natural and anthropogenic SO₄ sources and detection of spatial variations and seasonal changes among these sources. For instance, in the Llobregat River the input of fertilisers is well marked seasonally. Minimum values of δ³⁴S are reported during fertilization periods – from January to March – indicating a higher contribution of this source. The dual isotope approach, δ³⁴S and δ¹⁸O, is useful to better constrain the sources of SO₄. Moreover, in small-scale studies, where the inputs are well known and limited, the mixing models can be enhanced and the contribution of the different sources can be quantified to some extent.  相似文献   

Distribution and relative abundance of harbour porpoises (Phocoena phocoena L.), white-beaked dolphins (Lagenorhynchus albirostris Gray), and minke whales (Balaenoptera acutorostrata Lacepede) around the British Isles     

Northridge  Simon P.; Tasker  Mark L.; Webb  Andrew; Williams  James M. 《ICES Journal of Marine Science》1995,52(1):55-66

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A community-wide intercomparison exercise for the determination of dissolved iron in seawater     

Andrew R. Bowie  Eric P. Achterberg  Peter L. Croot  Hein J.W. de Baar  Patrick Laan  James W. Moffett  Simon Ussher  Paul J. Worsfold 《Marine Chemistry》2006

The first large-scale international intercomparison of analytical methods for the determination of dissolved iron in seawater was carried out between October 2000 and December 2002. The exercise was conducted as a rigorously “blind” comparison of 7 analytical techniques by 24 international laboratories. The comparison was based on a large volume (700 L), filtered surface seawater sample collected from the South Atlantic Ocean (the “IRONAGES” sample), which was acidified, mixed and bottled at sea. Two 1-L sample bottles were sent to each participant. Integrity and blindness were achieved by having the experiment designed and carried out by a small team, and overseen by an independent data manager. Storage, homogeneity and time-series stability experiments conducted over 2.5 years showed that inter-bottle variability of the IRONAGES sample was good (< 7%), although there was a decrease in iron concentration in the bottles over time (0.8–0.5 nM) before a stable value was observed. This raises questions over the suitability of sample acidification and storage.  相似文献