11 research outputs found
Evolution of the Most Massive Galaxies to z=0.6: I. A New Method for Physical Parameter Estimation
We use principal component analysis (PCA) to estimate stellar masses, mean
stellar ages, star formation histories (SFHs), dust extinctions and stellar
velocity dispersions for ~290,000 galaxies with stellar masses greater than
$10^{11}Msun and redshifts in the range 0.4<z<0.7 from the Baryon Oscillation
Spectroscopic Survey (BOSS). We find the fraction of galaxies with active star
formation first declines with increasing stellar mass, but then flattens above
a stellar mass of 10^{11.5}Msun at z~0.6. This is in striking contrast to
z~0.1, where the fraction of galaxies with active star formation declines
monotonically with stellar mass. At stellar masses of 10^{12}Msun, therefore,
the evolution in the fraction of star-forming galaxies from z~0.6 to the
present-day reaches a factor of ~10. When we stack the spectra of the most
massive, star-forming galaxies at z~0.6, we find that half of their [OIII]
emission is produced by AGNs. The black holes in these galaxies are accreting
on average at ~0.01 the Eddington rate. To obtain these results, we use the
stellar population synthesis models of Bruzual & Charlot (2003) to generate a
library of model spectra with a broad range of SFHs, metallicities, dust
extinctions and stellar velocity dispersions. The PCA is run on this library to
identify its principal components over the rest-frame wavelength range
3700-5500A. We demonstrate that linear combinations of these components can
recover information equivalent to traditional spectral indices such as the
4000A break strength and HdA, with greatly improved S/N. This method is able to
recover physical parameters such as stellar mass-to-light ratio, mean stellar
age, velocity dispersion and dust extinction from the relatively low S/N BOSS
spectra. We examine the sensitivity of our stellar mass estimates to the input
parameters in our model library and the different stellar population synthesis
models.Comment: 20 pages, 18 Figures, submitted to MNRA
Additive and Nonadditive Genetic Effects on Milk Production in Dairy Cattle: Evidence for Major Individual Heterosis
Stand level volume increment in relation to leaf area index of Austrocedrus chilensis and Nothofagus dombeyi mixed forests of Patagonia, Argentina
Thigh-length compression stockings and DVT after stroke
Controversy exists as to whether neoadjuvant chemotherapy improves survival in patients with invasive bladder cancer, despite randomised controlled trials of more than 3000 patients. We undertook a systematic review and meta-analysis to assess the effect of such treatment on survival in patients with this disease
Biomass and nutrient distribution in eucalypt plantations growing on rehabilitated bauxite mines
SPECTROSCOPIC DETERMINATION OF THE LOW-REDSHIFT TYPE Ia SUPERNOVA RATE FROM THE SLOAN DIGITAL SKY SURVEY
Protecting Privacy and Controlling Bureaucracies: Constraints of British Constitutional Principles
Ecological sensitivity of marl lakes to nutrient enrichment: evidence from Hawes Water, UK
Highly calcareous (marl) lakes are infrequent but important freshwater ecosystems, protected under the EU Habitats and Species Directive. Chara lakes have been considered resistant to eutrophication owing to the self-stabilising properties of charophyte meadows. However, the opposite is suggested by the large-scale biodiversity declines in marl lake taxa in Europe, and evidence of charophyte sensitivity to eutrophication. We combined contemporary, palaeolimnological and archival methods to investigate the eutrophication of Hawes Water, a shallow marl lake in north-west England (U.K.). Changes in aquatic macrophyte and invertebrate communities were reconstructed through the analysis of historical macrophyte surveys and sedimentary plant and animal macrofossils in two dated sediment cores from the littoral and deep zones of the lake. In addition, chlorophyll and carotenoid pigments were analysed to track changes in primary production from benthic and pelagic areas. Substantial changes in macrophyte communities were detected over centennial timescales, suggesting high ecosystem sensitivity considering the presently moderate phosphorus concentrations in Hawes Water (mean annual total phosphorus 20 μg L-1). Two apparent periods of threshold-like change were identified from the sediment record: (i) changes in cyanobacteria (aphanizophyll + myxoxanthophyll to canthaxanthin + zeaxanthin) and potentially in nutrient stoichiometry, reductions in the maximum macrophyte colonisation depth and water clarity, reduced charophyte and Potamogeton diversity, and increases in Nymphaeaceae; and (ii) severe reductions in light availability inferred from subdecadal doubling in phytoplankton abundance, substantial increases in Daphnia abundance and the extinction of charophytes from higher water depths. Further, change in both the littoral and deeper water has confined key marl lake taxa to smaller niches. In the littoral, increasing siltation and reed and Nymphaeaceae densities caused extinction of Littorella uniflora in the early 1900s and have reduced the evenness of Characeae with suspected imminent extinction of two highly localised Chara spp. In the deeper water, upslope creep of maximum colonisation depth has reduced habitat for intermediate-depth marl lake taxa leading to the loss of four Potamogeton and one Chara species, and replacement of these taxa by Nuphar lutea. The large changes in macrophyte community composition and increased incidences of turbid water have reduced the distinctive and valued marl lake features of Hawes Water, indicating that marl lakes can, as a habitat type, be highly sensitive to eutrophication. The persistence of abundant generalist macrophyte species at considerable water depth may be a feature of high-alkalinity lakes in clearwater, macrophyte-dominated states, but is a distinct eutrophication response in marl lakes rather than an indication of resistance to eutrophication