The star-formation histories of elliptical galaxies across the fundamental plane

We present the first results from a study designed to test whether, given high-quality spectrophotometry spanning the mid-UV--optical wavelength regime, it is possible to distinguish the metal content (Z) and star-formation history (sfh) of individual elliptical galaxies with sufficient accuracy to establish whether their formation history is linked to their detailed morphology and position on the Fundamental Plane. From a detailed analysis of UV-optical spectrophotometry of the `cuspy' elliptical galaxy NGC 3605 and the giant elliptical NGC 5018 we find that: 1) optical spectra with l > 3500 A may not contain sufficient data to robustly uncover all the stellar populations present in individual galaxies, even in such relatively passive objects as ellipticals, 2) the addition of the UV data approaching l = 2500 A holds the key to establishing well-constrained sfhs, from which we can infer a formation and evolution history which is consistent with their photometric properties, 3) despite the superficial similarity of their spectra, the two galaxies have very different `recent' sfhs -- the smaller, cuspy elliptical NGC 3605 contains a high-Z population of age ~= 1 Gyr, and has a position on the fundamental plane typical of the product of a low-z gas-rich merger (most likely at z ~ 0.08), while the giant elliptical NGC 5018, with a sub-solar secondary population, appears to have gained its more recent stars via mass transfer / accretion of gas from its spiral companion, 4) despite these differences in detailed history, more than 85% of the stellar mass of both galaxies is associated with an old (9-12 Gyr) stellar population of near-solar Z. This pilot study provides strong motivation for the construction and analysis of high-quality UV-optical spectra for a substantial sample of ellipticals spanning the Fundamental Plane.Comment: 11 pages, 10 figures, submitted to MNRAS, revised versio

Loss of star forming gas in SDSS galaxies

Using the star formation rates from the SDSS galaxy sample, extracted using the MOPED algorithm, and the empirical Kennicutt law relating star formation rate to gas density, we calculate the time evolution of the gas fraction as a function of the present stellar mass. We show how the gas-to-stars ratio varies with stellar mass, finding good agreement with previous results for smaller samples at the present epoch. For the first time we show clear evidence for progressive gas loss with cosmic epoch, especially in low-mass systems. We find that galaxies with small stellar masses have lost almost all of their cold baryons over time, whereas the most massive galaxies have lost little. Our results also show that the most massive galaxies have evolved faster and turned most of their gas into stars at an early time, thus strongly supporting a downsizing scenario for galaxy evolution.Comment: 29 pages, 9 figures, ApJ, accepte

Canadian Chicken Industry: Consumer Preferences, Industry Structure and Producer Benefits from Investment in Research and Advertising

The Canadian chicken industry has operated under supply management since the mid-1970s. Canadian consumer preferences for chicken have grown dramatically since then possibly in response to concerns about health and the levels of fat and cholesterol in red meats. However Canadian consumers are also looking for convenience with their food purchases. Canadians are buying their chicken in frozen further processed forms, fresh by cut without skin and bone and in a variety of other different ways reflecting their unique willingness to pay for various attributes. There is also an increasing trend for retailers and processors to brand the fresh chicken product sold through grocery stores (for example, Maple Leaf Prime). The preferences Canadian consumer have for various chicken products, the prices they are comfortable paying and the strategies followed by processors/retailers can directly affect the outcomes of industry wide strategies such as investment in generic advertising and research or the impact of international market changes such as border closures. This research is an initial attempt to quantify Canadian consumer preferences – for fresh product by type – for product by level of processing – for chicken product by cut - for fresh chicken by brand - to examine the impact of substitutability on a variety of market shocks. The various different disaggregations of Canadian chicken consumption are used in a number of simulation models to illustrate how important preferences are to producer returns when there are market shocks. If Canadians found all chicken products available in the grocery store to be perfectly substitutable then previous policy analysis assuming chicken is one homogeneous product would be sufficient for industry policy analysis purposes. If Canadians view all the different chicken products as imperfectly substitutable and given that various chicken products are produced in relatively fixed proportions (white and dark meat, for example) further understanding of how consumers make their purchase decisions could enhance the industries ability to predict outcomes. For example, border closing to Canadian exports ( as a result of an Avian influenza outbreak, for example) would result in a significant increase in the dark meat products available for sale through Canadian grocery stores. The results presented in this research could provide a clue as to how much dark meat prices might decline while white meat prices might remain unaffected. The results reported suggest that at the consumer level, chicken fresh and frozen products are not perceived to be perfect substitutes, within a narrow category such as fresh chicken breasts, they are not perceived as even close substitutes, within the fresh category branded products such as those developed by Lilydale and Maple Leaf are not perceived as perfect substitutes. As well, an initial look at the demand for individual chicken products by household suggests that there is far from a common buying pattern across Canadian households, even within a single province. The results also suggest that health and convenience attributes are driving Canadian consumer preferences. Simulation results highlight the fact that pricing strategies followed by major processors/retailers within Canada can influence the returns to generic advertising and research. Further research could provide additional robust estimates of the chicken product substitutability existing in the Canadian market and an increased understanding of the market characteristics currently operating. The results presented here suggest that further work in this area is important for the chicken industry to pursue.consumer behaviour, chicken consumption, differentiated products, Consumer/Household Economics, Demand and Price Analysis, Food Consumption/Nutrition/Food Safety, Marketing, D12, Q11, Q18,

The Complete Star Formation History of the Universe

The determination of the star-formation history of the Universe is a key goal of modern cosmology, as it is crucial to our understanding of how structure in the Universe forms and evolves. A picture has built up over recent years, piece-by-piece, by observing young stars in distant galaxies at different times in the past. These studies indicated that the stellar birthrate peaked some 8 billion years ago, and then declined by a factor of around ten to its present value. Here we report on a new study which obtains the complete star formation history by analysing the fossil record of the stellar populations of 96545 nearby galaxies. Broadly, our results support those derived from high-redshift galaxies elsewhere in the Universe. We find, however, that the peak of star formation was more recent - around 5 billion years ago. Our study also shows that the bigger the stellar mass of the galaxy, the earlier the stars were formed. This striking result indicates a very different formation history for high- and low-mass formation.Comment: Accepted by Nature. Press embargo until publishe

Stellar atmosphere parameters with MAx, a MAssive compression of x^2 for spectral fitting

MAx is a new tool to estimate parameters from stellar spectra. It is based on the maximum likelihood method, with the likelihood compressed in a way that the information stored in the spectral fluxes is conserved. The compressed data are given by the size of the number of parameters, rather than by the number of flux points. The optimum speed-up reached by the compression is the ratio of the data set to the number of parameters. The method has been tested on a sample of low-resolution spectra from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey for the estimate of metallicity, effective temperature and surface gravity, with accuracies of 0.24 dex, 130K and 0.5 dex, respectively. Our stellar parameters and those recovered by the SEGUE Stellar Parameter Pipeline agree reasonably well. A small sample of high-resolution VLT-UVES spectra were also used to test the method and the results have been compared to a more classical approach. The speed and multi-resolution capability of MAx combined with its performance compared with other methods indicates that it will be a useful tool for the analysis of upcoming spectral surveys.Comment: 17 pages, 10 figures, minor changes after the chief language editor. A&A, in pres

Access to recreational physical activities by car and bus : an assessment of socio-spatial inequalities in mainland Scotland

Obesity and other chronic conditions linked with low levels of physical activity (PA) are associated with deprivation. One reason for this could be that it is more difficult for low-income groups to access recreational PA facilities such as swimming pools and sports centres than high-income groups. In this paper, we explore the distribution of access to PA facilities by car and bus across mainland Scotland by income deprivation at datazone level. GIS car and bus networks were created to determine the number of PA facilities accessible within travel times of 10, 20 and 30 minutes. Multilevel negative binomial regression models were then used to investigate the distribution of the number of accessible facilities, adjusting for datazone population size and local authority. Access to PA facilities by car was significantly (p<0.01) higher for the most affluent quintile of area-based income deprivation than for most other quintiles in small towns and all other quintiles in rural areas. Accessibility by bus was significantly lower for the most affluent quintile than for other quintiles in urban areas and small towns, but not in rural areas. Overall, we found that the most disadvantaged groups were those without access to a car and living in the most affluent areas or in rural areas

Identifying phase synchronization clusters in spatially extended dynamical systems

We investigate two recently proposed multivariate time series analysis techniques that aim at detecting phase synchronization clusters in spatially extended, nonstationary systems with regard to field applications. The starting point of both techniques is a matrix whose entries are the mean phase coherence values measured between pairs of time series. The first method is a mean field approach which allows to define the strength of participation of a subsystem in a single synchronization cluster. The second method is based on an eigenvalue decomposition from which a participation index is derived that characterizes the degree of involvement of a subsystem within multiple synchronization clusters. Simulating multiple clusters within a lattice of coupled Lorenz oscillators we explore the limitations and pitfalls of both methods and demonstrate (a) that the mean field approach is relatively robust even in configurations where the single cluster assumption is not entirely fulfilled, and (b) that the eigenvalue decomposition approach correctly identifies the simulated clusters even for low coupling strengths. Using the eigenvalue decomposition approach we studied spatiotemporal synchronization clusters in long-lasting multichannel EEG recordings from epilepsy patients and obtained results that fully confirm findings from well established neurophysiological examination techniques. Multivariate time series analysis methods such as synchronization cluster analysis that account for nonlinearities in the data are expected to provide complementary information which allows to gain deeper insights into the collective dynamics of spatially extended complex systems

Very high energy gamma rays from the direction of Sagittarius A*.

We report the detection of a point-like source of very high energy (VHE) -rays coincident within 1' of Sgr A *, obtained with the HESS array of Cherenkov telescopes. The -rays exhibit a power-law energy spectrum with a spectral index of and a flux above the 165 GeV threshold of m -2 s -1. The measured flux and spectrum differ substantially from recent results reported in particular by the CANGAROO collaboration

The Energy Spectrum of TeV Gamma-Rays from the Crab Nebula as measured by the HEGRA system of imaging air Cherenkov telescopes

The Crab Nebula has been observed by the HEGRA (High-Energy Gamma-Ray Astronomy) stereoscopic system of imaging air Cherenkov telescopes (IACTs) for a total of about 200 hrs during two observational campaigns: from September 1997 to March 1998 and from August 1998 to April 1999. The recent detailed studies of system performance give an energy threshold and an energy resolution for gamma-rays of 500 GeV and ~ 18%, respectively. The Crab energy spectrum was measured with the HEGRA IACT system in a very broad energy range up to 20 TeV, using observations at zenith angles up to 65 degrees. The Crab data can be fitted in the energy range from 1 to 20 TeV by a simple power-law, which yields dJg/dE = (2.79+/-0.02 +/- 0.5) 10^{-7} E^{-2.59 +/- 0.03 +/- 0.05}, ph m^{-2} s^{-1} TeV^{-1} The Crab Nebula energy spectrum, as measured with the HEGRA IACT system, agrees within 15% in the absolute scale and within 0.1 units in the power law index with the latest measurements by the Whipple, CANGAROO and CAT groups, consistent within the statistical and systematic errors quoted by the experiments. The pure power-law spectrum of TeV gamma-rays from the Crab Nebula constrains the physics parameters of the nebula environment as well as the models of photon emission.Comment: to appear in ApJ, 29 pages, 6 figure