The effects of gas on morphological transformation in mergers: implications for bulge and disc demographics     

Philip F. Hopkins  Rachel S. Somerville  Thomas J. Cox †  Lars Hernquist  Shardha Jogee  Dusan Kere&#;  Chung-Pei Ma  Brant Robertson ‡  Kyle Stewart 《Monthly notices of the Royal Astronomical Society》2009,397(2):802-814

Transformation of discs into spheroids via mergers is a well-accepted element of galaxy formation models. However, recent simulations have shown that the bulge formation is suppressed in increasingly gas-rich mergers. We investigate the global implications of these results in a cosmological framework, using independent approaches: empirical halo-occupation models (where galaxies are populated in haloes according to observations) and semi-analytic models. In both, ignoring the effects of gas in mergers leads to the overproduction of spheroids: low- and intermediate-mass galaxies are predicted to be bulge-dominated (   B / T ∼ 0.5  at  <10¹⁰ M_⊙  , with almost no 'bulgeless' systems), even if they have avoided major mergers. Including the different physical behaviour of gas in mergers immediately leads to a dramatic change: bulge formation is suppressed in low-mass galaxies, observed to be gas-rich (giving   B / T ∼ 0.1  at  <10¹⁰ M_⊙  , with a number of bulgeless galaxies in good agreement with observations). Simulations and analytic models which neglect the similarity-breaking behaviour of gas have difficulty reproducing the strong observed morphology–mass relation. However, the observed dependence of gas fractions on mass, combined with suppression of bulge formation in gas-rich mergers, naturally leads to the observed trends. Discrepancies between observations and models that ignore the role of gas increase with redshift; in models that treat gas properly, galaxies are predicted to be less bulge-dominated at high redshifts, in agreement with the observations. We discuss implications for the global bulge mass density and future observational tests.  相似文献   

Scenarios of land use and land cover change in the conterminous United States: Utilizing the special report on emission scenarios at ecoregional scales     

Benjamin M. Sleeter  Terry L. Sohl  Michelle A. Bouchard  Ryan R. Reker  Christopher E. Soulard  William Acevedo  Glenn E. Griffith  Rachel R. Sleeter  Roger F. Auch  Kristi L. Sayler  Stephen Prisley  Zhiliang Zhu 《Global Environmental Change》2012,22(4):896-914

Global environmental change scenarios have typically provided projections of land use and land cover for a relatively small number of regions or using a relatively coarse resolution spatial grid, and for only a few major sectors. The coarseness of global projections, in both spatial and thematic dimensions, often limits their direct utility at scales useful for environmental management. This paper describes methods to downscale projections of land-use and land-cover change from the Intergovernmental Panel on Climate Change's Special Report on Emission Scenarios to ecological regions of the conterminous United States, using an integrated assessment model, land-use histories, and expert knowledge. Downscaled projections span a wide range of future potential conditions across sixteen land use/land cover sectors and 84 ecological regions, and are logically consistent with both historical measurements and SRES characteristics. Results appear to provide a credible solution for connecting regionalized projections of land use and land cover with existing downscaled climate scenarios, under a common set of scenario-based socioeconomic assumptions.  相似文献   

Direct Fourier transform mass spectral analysis of natural waters with low dissolved organic matter     

Rachel L. Sleighter  Georgina A. McKee  Patrick G. Hatcher 《Organic Geochemistry》2009,40(1):119-125

A major obstacle for characterizing dissolved organic matter (DOM) with ultrahigh resolution mass spectrometry has been its low concentrations in natural waters. Many previous mass spectrometric studies of both terrestrial and marine DOM typically have isolated and concentrated the DOM using solid phase C₁₈ extraction disks, ultrafiltration, or XAD resins, all of which are known to discriminate against many different classes of compounds. We have, for the first time, developed an approach to directly analyze natural water samples with less than 6 mg/l DOC (dissolved organic carbon), using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS). We demonstrate the sensitivity and ability of sequential selective ion accumulation (SSIA) to detect the thousands of components in a single freshwater DOM sample without any significant pretreatment. By utilizing SSIA, the baseline noise decreases while signal to noise ratios of the peaks increase, allowing for approximately 40% more formulas to be assigned to peaks in the mass spectra.  相似文献   

Paleo-climate of the Boise area, Idaho from the last glacial maximum to the present based on groundwater δH and δO compositions     

Melissa E. Schlegel  Steve Nelson  Rachel Henderson 《Quaternary Research》2009,71(2):172-214

A 30 ka paleo-climate record of the Boise area, Idaho, USA has been delineated using groundwater stable isotopic compositions. Groundwater ages are modern (cold batholith), 5-15 ka (thermal batholith) , 10-20 ka (frontal fault) , and 20-30 ka (Snake River plain thermal). The stable isotopic composition of groundwaters have been used as a surrogate for the stable isotopic composition of precipitation. Using δ²H and δ¹⁸O compositions, local groundwater lines (LGWL's) were defined for each system. Each LGWL has been evaluated with defined slopes of 6.94 and 8, respectively, and resulting deuterium excess values (d) were found for each groundwater system for each slope. Time dependent changes in moisture source humidity and temperature, and Boise area recharge temperatures, calculated from stable isotopic data and the deuterium excess factors, agree with previous paleo-climate studies. Results indicate that from the last glacial maximum to the present time the humidity over the ocean moisture source increased by 9%, sea surface temperature at the moisture source increased 6-7°C, and local Boise temperature increased by 4-5°C. A greater increase of temperature at the moisture source as compared to the Boise area may impart be due to a shift in the moisture source area.  相似文献   

Characterization of volatile organic compound emission sources in Fort Saskatchewan,Alberta using principal component analysis     

Rachel Mintz  Robert D. McWhinney 《Journal of Atmospheric Chemistry》2008,60(1):83-101

Volatile organic compounds (VOCs) were measured at two sites in a highly industrialized zone in western Canada from September 2004 to March 2006. Principal component analysis (PCA) with varimax rotation was performed on 30 VOCs to identify the pollution sources. Aliphatics, aromatics, and halogenated aliphatics were studied. The two monitoring sites were 11 km apart, with site 1 closer to the city of Fort Saskatchewan and site 2 predominantly down wind from the industrial sources. PCA results provided the basis for interpreting the relationship between the ambient 24-h integrated VOC samples and the emission sources in the region. Challenges existed in interpreting the PCA results in such a highly industrialized region; however a unique feature to this study was the fact that the region was home to the only 1,2-dichloroethane emitting facility in Canada. Other specific industry related VOCs in the region were vinyl chloride, styrene and HCFC-22. Making use of these specific VOCs in the PCA allowed for easy identification of an industrial contribution. For factors that were not easily distinguishable, further PCA tests were conducted using carbon monoxide concentrations, wind direction data and seasonal splitting of the samples. The analysis found that five factors accounted for 82% of the variance at site 1 and five factors accounted for 81% of the variance at site 2. The factor accounting for the highest variability (∼40%) at the two sites was the most difficult to interpret, but showed contributions from both industry and vehicle related emissions. Specific industrial sources were identified using 1,2-dichloroethane as a chemical tracer or by corroborating wind speed with known industry VOC emissions. Both sites had two factors identified as specific industry sources and these factors totaled to over 20% of the variance. Long range transport of stable halogenated compounds accounted for greater than 10% of the variance, and seasonal effects accounted for 5% of the variance.  相似文献   

Do abyssal scavengers use phytodetritus as a food resource? Video and biochemical evidence from the Atlantic and Mediterranean     

Rachel M. Jeffreys  Marc S.S. LavaleyeMagda J.N. Bergman  Gerard C.A. DuineveldRob Witbaard 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(4):415-428

Deep-sea benthic communities derive their energetic requirements from overlying surface water production, which is deposited at the seafloor as phytodetritus. Benthic invertebrates are the primary consumers of this food source, with deep-sea fish at the top of the trophic hierarchy. Recently, we demonstrated with the use of baited cameras that macrourid fish rapidly respond to and feed vigorously on large plant food falls mimicked by spinach (Jeffreys et al., 2010). Since higher plant remains are scarce in the deep-sea, with the exception of canyons, where terrestrial material has been observed, these results led us to ask if a more commonly documented plant material i.e. phytodetritus might form a food source for deep-sea fish and mobile scavenging megafauna. We simulated a phytodetritus dump at the seafloor in two contrasting environments (1) the NE Atlantic where carpets of phytodetritus have been previously observed and (2) the oligotrophic western Mediterranean, where the deposition of phytodetritus at the seafloor is a rare occurrence. We recorded the response of the scavenging fauna using an in situ benthic lander equipped with baited time-lapse cameras. In the NE Atlantic at 3000 m, abyssal macrourids and cusk-eels were observed ingesting the phytodetritus. The phytodetrital patch was significantly diminished within 2 h. Abundance estimates calculated from first arrival times of macrourids at the phytodetrital patch in the Atlantic corresponded with abundance estimates from video-transect indicating that fish were attracted to the scent of phytodetrital bait. In contrast to this, in the western Mediterranean at 2800 m a single macrourid was observed investigating the phytodetrital patch but did not feed from it. The phytodetrital patch was significantly diminished within 6.5 h as a result of mainly invertebrate activity. At 1900 m, Lepidion lepidion was observed near the lander and the bait, but did not feed. The phytodetrital patch remained intact until the end of the experiment. In the deployments in the Mediterranean abundance estimates from first arrival times at the bait, corrected for their body size, were lower than estimates obtained from video-transects and trawl catches. This suggests that the Mediterranean fish were not readily attracted to this food source. In contrast, invertebrates in the Balearic Sea were observed ingesting the phytodetritus bait despite the rare occurrence of phytodetritus dumps in the Mediterranean. Stable isotope values of the fish at both study sites, set within the context of the benthic food web, did not demonstrate a strong trophic link to phytodetritus. Fatty acid profiles of these fish indicated a strong link between their lipid pool and primary producers i.e. phytoplankton, which may be attributed to trophic transfer. The usefulness of fatty acid biomarkers in ascertaining deep-sea fish diets is discussed. Our study suggests that the abyssal grenadier C. armatus on the Atlantic Iberian margin is attracted to phytodetritus. However the exact contribution of this food source to the diet of macrourids in this area remains unresolved.  相似文献   

Paleolimnological comparison of algal changes in a clear-versus a brown-water lake over the last two centuries in the northeastern U.S.A     

Fowler  Rachel A.  Warner  Kate A.  Gawley  William G.  Saros  Jasmine E. 《Journal of Paleolimnology》2022,67(3):289-305

Journal of Paleolimnology - We reconstructed historical diatom and algal pigment records from a clear-water versus a brown-water lake in the northeastern U.S. to compare ecological responses to...  相似文献   

Highly conservative behaviour of bed sediment‐associated metals following extreme flooding     

Rachel R. Hurley  Jamie C. Woodward  James J. Rothwell 《水文研究》2019,33(8):1204-1217

On December 26, 2015 (Boxing Day), an exceptional flood event occurred in the Irwell catchment, United Kingdom, when the neighbouring Mersey catchment experienced a much more typical winter run‐off event. This provided an opportunity to examine the influence of high‐magnitude hydrological processes on the behaviour of fine‐grained metal‐contaminated bed sediments. Forty sites across the two catchments were sampled for channel bed fine sediment storage and sediment‐associated metal(loid) concentrations prior to, and following, the flooding. Sediments were analysed for total As, Cr, Cu, Pb, and Zn and then subjected to a five‐step sequential extraction procedure. Despite a significant reorganisation of fine‐grained (<63 μm) sediment storage, metal(loid) concentrations demonstrated markedly conservative behaviour with no significant difference observed between pre‐flooding and post‐flooding values across both catchments. Estimates of the channel bed storage of sediment‐associated metal(loid)s also showed minimal change as a result of the flooding. The metal partitioning data reveal only minor changes in the mobility of bed sediment‐associated metal(loid)s, indicating that such flood events do not increase the availability of sorbed contaminants in these catchments. Post‐flooding bed sediment metal(loid) loadings remain high, indicating persistent and long‐lasting sources of contamination within the Irwell and upper Mersey fluvial network.  相似文献   

Magnetic Environments of Young Stellar Objects     

Antonio Chrysostomou  Rachel Curran  David Aitken  Tim Jenness  Chris Davis 《Astrophysics and Space Science》2003,287(1-4):161-164

We report on early results of magnetic field measurements towards a sample of young stellar objects. The results show a variety of field configurations, some of which can be explained by conventional models, while others cannot. We find that the field in some cases is curved over large scales and influenced by the gas kinematics in the local environment. This implies that, at these scales at least, the magnetic field plays a passive rôle in the star formation process.  相似文献   

Estimating photometric redshifts with artificial neural networks     

Andrew E. Firth  Ofer Lahav  Rachel S. Somerville 《Monthly notices of the Royal Astronomical Society》2003,339(4):1195-1202

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