Extremely red galaxy counterparts to 7C radio sources     

Chris J. Willott  Steve Rawlings  Katherine M. Blundell 《Monthly notices of the Royal Astronomical Society》2001,324(1):1-17

We present RIJHK imaging of seven radio galaxies from the 7C Redshift Survey (7CRS) which lack strong emission lines and we use these data to investigate their spectral energy distributions (SEDs) with models that constrain their redshifts. Six of these seven galaxies have extremely red colours ( R − K >5.5) and we find that almost all of them lie in the redshift range 1< z <2. We also present near-infrared spectroscopy of these galaxies which demonstrate that their SEDs are not dominated by emission lines, although tentative lines, consistent with H α at z =1.45 and z =1.61, are found in two objects. Although the red colours of the 7CRS galaxies can formally be explained by stellar populations that are either very old or young and heavily reddened, independent evidence favours the former hypothesis. At z ∼1.5 at least 1/4 of powerful radio jets are triggered in massive (> L *) galaxies, which formed the bulk of their stars several Gyr earlier, that is at epochs corresponding to redshifts z ≳5. If a similar fraction of all z ∼1.5 radio galaxies are old, then extrapolation of the radio luminosity function shows that, depending on the radio source lifetimes, between 10 and 100 per cent of the near-IR selected extremely red object (ERO) population undergo a radio outburst at epochs corresponding to 1< z <2. An ERO found serendipitously in the field of one of the 7CRS radio sources appears to be a radio-quiet analogue of the 7CRS EROs with an emission line likely to be [O  ii ] at z =1.20. The implication is that some of the most massive elliptical galaxies formed the bulk of their stars at z ≳5 and these objects probably undergo at least two periods of active galactic nucleus activity: one at high redshift during which the black hole forms and another one at an epoch corresponding to z ∼1.5.  相似文献   

Tidally induced residual flows around an island due to both frictional and rotational effects     

R. D. Pingree  Linda Maddock 《Geophysical Journal International》1980,63(2):533-546

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Celtic Sea and Armorican current structure and the vertical distributions of temperature and chlorophyll     

R.D. Pingree  G.T. Mardell  P.M. Holligan  D.K. Griffiths  J. Smithers 《Continental Shelf Research》1982,1(1):99-116

Vertical sections of temperature and chlorophyll a across the slopes and shelf of the Celtic Sea in the summer show the characteristic regimes; oceanic, slope, shelf, frontal, and mixed. Increases of surface chlorophyll a are commonly observed along the shelf tidal fronts where the thermocline outcrops at the surface, and also at the shelf-break. The variations in phytoplankton biomass are most readily interpreted in terms of the effects of physical mixing processes due to wind and tide on the availability of inorganic nutrients and light energy. On the shelf, mixing processes, both due to internal waves, inertial currents, and to boundary induced turbulence caused by tidal shear associated with the sea floor, play an important role in determining the observed vertical structures. A numerical model is used to define regions where tidal mixing processes are likely to be relatively important and provides the physical framework for interpreting the temperature and chlorophyll a profiles.  相似文献   

Six-color observations of the Eclipsing binary AR Cas     

Katherine C. Gordon  Gerald E. Kron 《Astrophysics and Space Science》1973,23(2):403-416

Depths and phases of both minima of AR Cas in six colors in 1959 are presented. Analysis leads to a color distribution for the secondary component which corresponds to spectral type A5–A7.  相似文献   

Black Sea chemocline oscillations during the Holocene: molecular and isotopic studies of marginal sediments     

Yongsong Huang  Katherine H. Freeman  Richard T. Wilkin  Michael A. Arthur  A. Daniel Jones 《Organic Geochemistry》2000,31(12):642

We measured δ¹³C values of free and sulfur-bound lipids and framboidal pyrite-size distributions in three sediment cores from the southern margins of the Black Sea. The margin cores show a marked difference in the occurrence of biomarkers from green sulfur bacteria compared with the deep-basin cores, as a result of deepening of the chemocline resulting from enhanced mixing and/or decreased light-penetration as a consequence of high turbidity and productivity in shelf waters. Quantitation of biomarkers suggests that photic-zone anoxia along the shelf margin was generally absent during the deposition of unit I, although occurred during the deposition of Unit IIb at two sites.  相似文献   

Magnetic study of serpentinized harzburgites from the Islas Orcadas Fracture Zone     

Nazarova  Katherine A.  Wasilewski  Peter J.  Dick  Henry J.B. 《Marine Geophysical Researches》2000,21(5):475-488

Magnetic properties and bulk densities of 27 serpentinized harzburgite samples from the Islas Orcadas Fracture Zone, located in the vicinity of the Bouvet Triple Junction, have been measured and analyzed. Polished sections were examined using reflected light and scanning electron microscopy to characterize the size and geometric arrangement of opaque minerals. The relationship between the saturation magnetization (I_S) and remanent coercive force (H_R) is considered in terms of the amount of ferrimagnetic material and maghemitization. A suite of continental serpentinites from Canada is offered as contrast, to consider the role of weathering and maghemitization. Magnetite in the Islas Orcadas serpentinites is variably maghemitized, whereas continental serpentinites do not appear to contain maghemitized oxides. We verify this with optical microscopy, thermomagnetic analyses and cryogenic temperature cycling of saturation remanence. Maghemitization serves to reduce initial magnetic susceptibility, and introduce error in the use of I_S to evaluate the magnetic mode of magnetite. The presence of maghemite and the existence of a three dimensional vein network for magnetite geometry would suggest that magnetic hysteresis parameters can not reliably indicate grain size. Magnetic hysteresis ratios fall in a restricted range regardless of coercivity. The apparent grain size configured in a three dimensional vein network plus maghemitization might be responsible for this observation. Maghemitization does not affect thermal magnetic stability and enhances the geophysical importance of remanence in serpentinites. Paleomagnetic data suggest that important information about the geologic circumstances for oceanic rock serpentinization is embodied in the paleomagnetic records. This observation may be very important for generation of long wavelength aeromagnetic and possibly even satellite magnetic anomalies.  相似文献   

Global climate,energy, and economic implications of international energy offsets programs     

Katherine Calvin  Steven Rose  Marshall Wise  Haewon McJeon  Leon Clarke  Jae Edmonds 《Climatic change》2015,133(4):583-596

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Provenance of altered carbon phases and impact history of the Stac Fada Member,NW Scotland     

Arthur Goodwin  Romain Tartèse  Russell J. Garwood  Rhodri Jerrett  Katherine H. Joy 《Meteoritics & planetary science》2023,58(8):1099-1116

The Stac Fada Member (Stoer Group) is a ~1.2 Ga melt-rich impact breccia preserved and intermittently exposed along the NW coast of Scotland. Using a combination of x-ray diffraction and micro-Raman spectroscopy, we identify potential coesite that is spatially associated with micron-sized diamonds, as well as disordered carbon phases. Comparing the graphite G-band of disordered carbon phases in the impact breccia to samples from underlying units indicates that most of the carbon in the Stoer Group was ultimately derived from the underlying Lewisian basement. Disordered carbon phases within the Stac Fada Member have been modified by mild heating within a hot ejecta blanket rather than shock pressure. We also report the first evidence for impact diamonds discovered within the Stac Fada Member. These diamonds have an average Raman shift of 1328.5 cm⁻¹ and are present within both the impact breccia and the shocked gneiss clasts that are present in sandstones directly underlying the Stac Fada Member contact, and within sandstone rafts entrapped in the unit. These findings have implications for the timing of deposition of the Stac Fada Member, which must have occurred after ballistic ejection of Lewisian basement clasts during the impact event.  相似文献   

Deglaciation, basin formation and post-glacial climate change from a regional network of sediment core sites in Ohio and eastern Indiana     

Katherine C. Glover  Thomas V. Lowell  Gregory C. Wiles  Donald Pair  Patrick Applegate  Irena Hajdas 《Quaternary Research》2011,76(3):401-410

Many paleoclimate and landscape change studies in the American Midwest have focused on the Late Glacial and early Holocene time periods (~ 16–11 ka), but little work has addressed landscape change in this area between the Last Glacial Maximum and the Late Glacial (~ 22–16 ka). Sediment cores were collected from 29 new lake and bog sites in Ohio and Indiana to address this gap. The basal radiocarbon dates from these cores show that initial ice retreat from the maximal last-glacial ice extent occurred by 22 ka, and numerous sites that are ~ 100 km inside this limit were exposed by 18.9 ka. Post-glacial environmental changes were identified as stratigraphic or biologic changes in select cores. The strongest signal occurs between 18.5 and 14.6 ka. These Midwestern events correspond with evidence to the northeast, suggesting that initial deglaciation of the ice sheet, and ensuing environmental changes, were episodic and rapid. Significantly, these changes predate the onset of the Bølling postglacial warming (14.8 ka) as recorded by the Greenland ice cores. Thus, deglaciation and landscape change around the southern margins of the Laurentide Ice Sheet happened ~ 7 ka before postglacial changes were felt in central Greenland.  相似文献   

The role of biodegradation and photo-oxidation in the transformation of terrigenous organic matter   总被引：1，自引：0，他引：1  

Xiaojuan Feng  Katherine M. Hills  Andr J. Simpson  Joann K. Whalen  Myrna J. Simpson 《Organic Geochemistry》2011,42(3):262-274

Microbial and photochemical decomposition are two major processes regulating organic matter (OM) transformation in the global carbon cycle. However, photo-oxidation is not as well understood as biodegradation in terms of its impact on OM alteration in terrigenous environments. We examined microbial and photochemical transformation of OM and lignin derived phenols in two plant litters (corn leaves and pine needles). Plant litter was incubated in the laboratory over 3 months and compositional changes to OM were measured using nuclear magnetic resonance (NMR) and gas chromatography-mass spectrometry. We also examined the susceptibility of soil organic matter (SOM) to ultraviolet (UV) radiation. Solid-state ¹³C NMR spectra showed that O-alkyl type structures (mainly from carbohydrates) decreased during biodegradation and the loss of small carbohydrates and aliphatic molecules was observed by solution-state ¹H NMR spectra of water extractable OM from biodegraded litters. Photochemical products were detected in the aliphatic regions of NaOH extracts from both litter samples by solution-state ¹H NMR. Photo-oxidation also increased the solubility of SOM, which was attributed to the enhanced oxidation of lignin derived phenols and photochemical degradation of macromolecular SOM species (as observed by diffusion edited ¹H NMR). Overall, our data collectively suggests that while biodegradation predominates in litter decomposition, photo-oxidation alters litter OM chemistry and plays a role in destabilizing SOM in soils exposed to UV radiation.  相似文献