The DEEP2 galaxy redshift survey: evolution of the colour–density relation at  0.4 < z < 1.35      

Michael C. Cooper  Jeffrey A. Newman †  Alison L. Coil †  Darren J. Croton  Brian F. Gerke  Renbin Yan  Marc Davis  S. M. Faber  Puragra Guhathakurta  David C. Koo  Benjamin J. Weiner  Christopher N. A. Willmer ‡ 《Monthly notices of the Royal Astronomical Society》2007,376(4):1445-1459

Using a sample of 19 464 galaxies drawn from the DEEP2 Galaxy Redshift Survey, we study the relationship between galaxy colour and environment at  0.4 < z < 1.35  . We find that the fraction of galaxies on the red sequence depends strongly on local environment out to   z > 1  , being larger in regions of greater galaxy density. At all epochs probed, we also find a small population of red, morphologically early-type galaxies residing in regions of low measured overdensity. The observed correlations between the red fraction and local overdensity are highly significant, with the trend at   z > 1  detected at a greater than 5σ level. Over the entire redshift regime studied, we find that the colour–density relation evolves continuously, with red galaxies more strongly favouring overdense regions at low z relative to their red-sequence counterparts at high redshift. At   z ≳ 1.3  , the red fraction only weakly correlates with overdensity, implying that any colour dependence to the clustering of  ∼ L *  galaxies at that epoch must be small. Our findings add weight to existing evidence that the build-up of galaxies on the red sequence has occurred preferentially in overdense environments (i.e. galaxy groups) at   z ≲ 1.5  . Furthermore, we identify the epoch  ( z ∼ 2)  at which typical  ∼ L *  galaxies began quenching and moved on to the red sequence in significant number. The strength of the observed evolutionary trends at  0 < z < 1.35  suggests that the correlations observed locally, such as the morphology–density and colour–density relations, are the result of environment-driven mechanisms (i.e. 'nurture') and do not appear to have been imprinted (by 'nature') upon the galaxy population during their epoch of formation.  相似文献   

Weighing the cusp at the Galactic Centre     

N. Mouawad  A. Eckart  S. Pfalzner  R. Schdel  J. Moultaka  R. Spurzem 《Astronomische Nachrichten》2005,326(2):83-95

As stars close to the galactic centre have short orbital periods it has been possible to trace large fractions of their orbits in the recent years. Previously the data of the orbit of the star S2 have been fitted with Keplerian orbits corresponding to a massive black hole (MBH) with a mass of M_BH = 3–4 × 10⁶M_⊙ implying an insignificant cusp mass. However, it has also been shown that the central black hole resides in a ∼1″ diameter stellar cluster of a priori unknown mass. In a spherical potential which is neither Keplerian nor harmonic, orbits will precess resulting in inclined rosetta shaped trajectories on the sky. In this case, the assumption of non‐Keplerian orbits is a more physical approach. It is also the only approach through which cusp mass information can be obtained via stellar dynamics of the cusp members. This paper presents the first exemplary modelling efforts in this direction. Using positional and radial data of star S2, we find that there could exist an unobserved extended mass component of several 10⁵M_⊙ forming a so‐called ‘cusp’ centered on the black hole position. Considering only the fraction of the cusp mass Mequation/tex2gif-inf-4.gif within the apo‐center of the S2 orbit we find as an upper limit that Mequation/tex2gif-inf-6.gif/(M_BH + Mequation/tex2gif-inf-9.gif) ≤ 0.05. A large extended cusp mass, if present, is unlikely to be composed of sub‐solar mass constituents, but could be explained rather well by a cluster of high M/L stellar remnants, which we find to form a stable configuration. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

NIR/Optical Interferometry     

Andreas Eckart 《Astronomische Nachrichten》2005,326(7):559-573

E01 VLTI‐PRIMA Fringe Tracking Testbed E02 The Fringe and Flexure Tracking System for the LBT interferometric camera LINC‐NIRVANA E03 GRAVITY: The AO assisted, two object beam combiner instrument for the VLTI E04 (Re)Solving the dynamic atmospheres of carbon‐rich giants E05 Do's and Don'ts of MIDI Data‐reduction E06 Bispectrum speckle imaging of the ultracompact HII region K3‐50A E07 Differential astrometry and astrometric planet searches with the VLTI E08 First AU‐scale observations of V1647 Ori: The outbursting young star in the McNeil's Nebula E09 Mid‐infrared imaging at the VLTI: An APreS‐MIDI image reconstruction study E10 VLTI/MIDI observation of the silicate carbon star Hen 38 (IRAS08002‐3803): Silicate dust reservoir spatially resolved for the first time E11 Mid‐infrared spectro‐interferometric observation of the Mira variable RR Sco with the VLTI/MIDI instrument E12 Scientific Prospects for VLTI in the Galactic Centre: Getting to the Schwarzschild Radius E13 VLTI near‐infrared observations of the stellar multiple system δ Velorum E14 The first VLTI observations of the Galactic Center E15 Bispectrum speckle interferometry of the massive protostellar outflow source IRAS 23151+5912 E16 Interferometric Observations of Infrared Companions with MIDI E17 Evolution and radial distribution of dust in the inner 1‐10A.U. of circumstellar disks around low‐mass young stellar objects. E18 Near‐infrared Interferometry with the AMBER Instrument of the VLTI E19 APreS‐MIDI ‐ Interferometic Imaging in the Mid‐Infrared E20 Mining the sky: Selection of extragalactic targets for interferometric observations  相似文献   

Linking meteorites to their asteroid parent bodies: The capabilities of dust analyzer instruments during asteroid flybys     

Lisa Maria Eckart  Jon K. Hillier  Frank Postberg  Simone Marchi  Zoltan Sternovsky 《Meteoritics & planetary science》2023,58(10):1449-1468

Linking meteorites to their asteroid parent bodies remains an outstanding issue. Space-based dust characterization using impact ionization mass spectrometry is a proven technique for the compositional analysis of individual cosmic dust grains. Here we investigate the feasibility of determining asteroid compositions via cation mass spectrometric analyses of their dust ejecta clouds during low (7–9 km s⁻¹) velocity spacecraft flybys. At these speeds, the dust grain mass spectra are dominated by easily ionized elements and molecular species. Using known bulk mineral volume abundances, we show that it is feasible to discriminate the common meteorite classes of carbonaceous chondrites, ordinary chondrites, and howardite–eucrite–diogenite achondrites, as well as their subtypes, relying solely on the detection of elements with ionization efficiencies of ≤700 or ≤800 kJ mol⁻¹, applicable to low (~7 km s⁻¹) and intermediate (~9 km s⁻¹) flyby speed scenarios, respectively. Including the detection of water ion groups enables greater discrimination between certain meteorite types, and flyby speeds ≥10 km s⁻¹ enhance the diagnostic capabilities of this technique still further. Although additional terrestrial calibration is required, this technique may allow more unequivocal asteroid-meteorite connections to be determined by spacecraft flybys, emphasizing the utility of dust instruments on future asteroid missions.  相似文献   

New Albian macro- and palynoflora from the Negev (Israel) with description of a new gymnosperm morphotaxon     

Valentin Krassilov  Eckart Schrank 《Cretaceous Research》2011,32(1):13-29

New plant macrofossil localities are found in the middle-upper part of the Albian Upper Hatira Formation of Makhtesh Qatan, an erosion crater in the northern Negev. These are so far the only outcrop localities in the Negev containing plant compressions and well-preserved sporomorphs. Their age assignments are controlled by the ammonite Knemiceras records below and above the plant-bearing sequence in the adjacent Makhtesh Hatira. The macrofossil assemblages are strikingly different in the sandy fluvial and shaly lacustrine facies, the former being dominated by Araucaria, Athrotaxopsis, Brachyphyllum and pinnatifid Sapindopsis, comparable at the plant assemblage and leaf morphological levels to the early to early late Albian assemblage of the North American Potomac flora. The lacustrine shale macrofossil assemblages appear archaic on account of their diverse pteridophyte component and sparse angiosperm remains. A new supposedly gnetophytic genus and species Qataniaria noae Krassilov, gen. et sp. nov. is dominant in the shale horizon. The sporomorph assemblages are strongly dominated by psilate trilete spores (87-93%). In the absence of elaterate forms, the angiosperm pollen Afropollis jardinus, Pennipollis, Tricolpites spp. and Walkeripollis sp. is consistent with the early Albian age. The abundance and diversity of conifers and the prominence of the fern bog assemblage suggest a relatively humid phase of the regional Albian climates.  相似文献   

The nature of high-redshift galaxies     

Rachel S. Somerville  Joel R. Primack  S. M. Faber 《Monthly notices of the Royal Astronomical Society》2001,320(4):504-528

Using semi-analytic models of galaxy formation set within the cold dark matter (CDM) merging hierarchy, we investigate several scenarios for the nature of the high-redshift     ) Lyman-break galaxies (LBGs). We consider a 'collisional starburst' model in which bursts of star formation are triggered by galaxy–galaxy mergers, and find that a significant fraction of LBGs are predicted to be starbursts. This model reproduces the observed comoving number density of bright LBGs as a function of redshift and the observed luminosity function at     and     with a reasonable amount of dust extinction. Model galaxies at     have star formation rates, half-light radii,     colours and internal velocity dispersions that are in good agreement with the data. Global quantities such as the star formation rate density and cold gas and metal content of the Universe as a function of redshift also agree well. Two 'quiescent' models without starbursts are also investigated. In one, the star formation efficiency in galaxies remains constant with redshift, while in the other, it scales inversely with disc dynamical time, and thus increases rapidly with redshift. The first quiescent model is strongly ruled out, as it does not produce enough high-redshift galaxies once realistic dust extinction is accounted for. The second quiescent model fits marginally, but underproduces cold gas and very bright galaxies at high redshift. A general conclusion is that star formation at high redshift must be more efficient than locally. The collisional starburst model appears to accomplish this naturally without violating other observational constraints.  相似文献   

Hot granulite nappes — Tectonic styles and thermal evolution of the Proterozoic granulite belts in East Africa   总被引：1，自引：0，他引：1  

Harald Fritz  Veronika Tenczer  Christoph Hauzenberger  Eckart Wallbrecher  Sospeter Muhongo   《Tectonophysics》2009,477(3-4):160

A section through the Neoproterozoic Mozambique Belt of Tanzania exposes western foreland (Archaean Tanzania Craton and Palaeoproterozoic Usagaran Belt), marginal (Western Granulites) and eastern, internal (Eastern Granulites) portions of the orogen. The assembly of granulite nappes at ca. 620 Ma displays westward emplacement along an eastward deepening basal decollement and forward propagation of thrusts, climbing from the deep crust to the surface. This goes along with eastward increase of syntectonic temperatures, derived from prevalent deformation mechanisms, and eastward decrease of the kinematic vorticity number. Distinctly different pressure - temperature paths with a branch of isothermal decompression (ITD) in Western Granulites and isobaric cooling (IBC) in Eastern Granulites reflect residence times of rocks within lower crustal levels. Western Granulites, exhumed rapidly at the orogen margin, display ITD and non-coaxial fabrics. Eastern Granulites in the internal orogen portions escaped from rapid exhumation and show IBC and co-axial flow fabrics. The vertical variation of structural elements, i.e. basement — cover relations within the Eastern Granulites, shows decoupling between lower and middle crust with horizontal west — east stretching in the basement and horizontal west — east shortening in the cover.A model of hot fold nappes [Beaumont, C., Nguyen, M.H., Jamieson, R.A., Ellis, S., 2006. Crustal flow modes in large hot orogens. In: Law, R.D., Searle, M.P., Godin, L., (eds). Channel Flow, Ductile Extrusion and Exhumation in Continental Collision Zones. Geological Society, London, Special Publications. vol. 268, 91–145] is adopted to explain flow diversity in the deep crust. The lower crust represented by Eastern Granulite basement flowed coaxially outwards (westward) in response to thickened crust and elevated gravitational forces, supported by a melt-weakened, viscous channel at the crustal base. Horizontal flow with rates faster than thermal equilibration gave rise to isobaric cooling. Simultaneously the mid crust (Eastern Granulite cover) was shortened when hot fold nappes moved along upward climbing thrust planes. Western Granulites preserved isothermal decompression through exhumation by thrusting and coeval erosion at the orogen front.Two different styles define the Neoproterozoic East African Orogen between northern Egypt and southern Mozambique. The Arabian Nubian Shield in the north is classified as small and cold orogen in which thin — skinned thrusting was associated with lateral extrusion. The Central Mozambique Belt in Tanzania/Southern Kenya is classified as large and hot orogen characterized by thick-skinned thrusting and assembly of large granulite nappes.  相似文献   

The influence of suspended cohesive sediments on boundary-layer structure and erosive activity of turbulent seawater flow     

Giselher Gust  Eckart Walger 《Marine Geology》1976,22(3):189-206

Velocity and suspension measurements in the logarithmic layer of hydraulically smooth turbulent tidal flow from the North Sea are reported. The data were not compatible with the assumption of Newtonian flow for the experimental seawater—clay suspension.Laboratory measurements were initiated with mud and seawater from the North Sea in which the boundary-layer structure of this two-phase flow was measured down into the viscous sublayer. The dilute seawater—clay suspension was a mixture of illite, kaolinite and chlorite minerals with concentrations less than 380 mg/l and exhibited turbulent drag reduction.By reviewing flow measurements of other authors it is suggested that turbulent drag reduction occurs on a geophysical scale if the flows transport cohesive sediments. It is proposed that drag reduction is caused by dynamic interaction between turbulent shear strain in the flow and deformation of aggregates.As a consequence, the values of the critical friction velocity $\text{u}{}_{\mathrm{<mtext>1\; </mtext><mtext>crit</mtext>}}$ and of erosion rates must be reviewed for cohesive bottom materials. Normally they were obtained under the assumption of a Newtonian flow structure which is not applicable if the flow transports cohesive sediments.To detect the occurrence of drag reduction in geophysical boundary layers (hydraulically smooth), flow measurements must be performed down into the viscous sublayer. The adequate velocity sensors must have a diameter of ?1 mm.  相似文献   

The DEEP2 galaxy redshift survey: the evolution of the blue fraction in groups and the field     

Brian F. Gerke  Jeffrey A. Newman  S. M. Faber  Michael C. Cooper  Darren J. Croton  Marc Davis  Christopher N. A. Willmer  Renbin Yan  Alison L. Coil  Puragra Guhathakurta  David C. Koo  Benjamin J. Weiner 《Monthly notices of the Royal Astronomical Society》2007,376(4):1425-1444

  相似文献   

Long Range Science Perspectives for the VLTI     

A. Eckart  T. Bertram  N. Mouawad  T. Viehmann  C. Straubmeier  J. Zuther 《Astrophysics and Space Science》2003,286(1-2):269-276

VLTI interferometry will allow imaging of galactic and extragalactic sources with milliarcsecond angular resolution. For moderately bright sources the spectral resolution will be of the order of 10000. These capabilities will allow detailed studies of solar system objects, stars, proto-planetary systems and the detection of hot extra-solar planets. The observations of galactic nuclei will allow unprecedented measurements of physical parameters in these systems. VLTI will be a prime instrument to study the immediate environment of the massive black hole at the center of the Milky Way. With the exception of a few `self-referencing' sources the observations of extragalactic nuclei will benefit from an extended capability for simultaneous measurements of nearby reference sources for fringe tracking. With beam combination instruments like AMBER, MIDI, PRIMA, and GENIE the VLTI will reach full maturity at a time when other interferometric instruments at different wavelengths will be fully operational. Most important are ALMA (in the mm- and sub-mm-domain), LOFAR and SKA (in the radio meter to centimeter domain) and of course VLB-networks in the radio, and other – at that time –well developed interferometers in the optical. A major scientific potential of future scientific VLTI programs will lie in an efficient combination of these high angular resolution capabilities. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献