Relationship between blood attributes and predicted breeding value for milk yield in calves

International audienc

Diatom and silicoflagellate fluxes at the Walvis Ridge: An environment influenced by coastal upwelling in the Benguela system

Seasonal fluctuations in the total particle, biogenic opal, diatom and silicoflagellate fluxes were observed in sediment traps deployed at 599 m and 1648 m in the Walvis Ridge area, within the Benguela upwelling system, from March 1989 to March 1990 (station WR 2: 20°02.8′S, 09°09.3′E). Fluxes were directly related to wind stress variations (wind maxima preceding flux maxima by several weeks), and inversely related to SST changes (derived from measured concentrations of C37 alkenones; range: 14.6°–23.6°C). The biogenic particle composition at different depths reflected the complicated hydrology of the area with a combination of tropical, temperate and subantarctic water masses. Biogenic opal content varied from about 2 to 12% of the total mass flux in the upper trap and from about 4 to 17% in the lower trap. Diatoms were the main contributor to the opal fraction (mean daily flux of ca. 5.5 * 106 valves m−2 day−1), followed by silicoflagellates (ca. 2.6 * 105 skeletons m−2 day−1). Two seasonal maxima, in May and June (austral autumn) and from October to November (austral spring), were observed; silicoflagellates yielded also a third moderate maximum in August/September (austral winter). At 1648 m fluxes peaked from May to July (data were available for the period 18 Mar to 27 Aug 1989 only). Few diatoms were abundant; 19 taxa accounted for 50% of all the diatoms identified, and about 32 for the 75% level. Specific diversity of diatoms at 599 m was highest during times of lowest fluxes, in the austral winter, late spring and summer. The diatom taxa occurring at 599 m and at 1648 m were the same, with some flux enrichment with depth due to advection of particles into the lower trap by resuspension and downslope movement. The relatively high concentrations of the Antarctic-Subantarctic species Fragilariopsis kerguelensis in the upper trap solely, was probably linked to selective entrainment and transport within a ring of southerly origin (south of the Subantarctic/Subtropical Convergence Zone). The enrichment of moderately resistant and robust taxa in the sediments in conjunction with the rarity or absence of delicate taxa points to preferential concentration in the sediments of some taxa and dissolution of others. The occurrence of phytoliths in the traps and in the sediment sample can be linked to the “berg” winds, which are typical for the entire Benguela region during fall and winter

Life cycle assessment (LCA) of a battery home storage system based on primary data

While the market for battery home storage systems (HSS) is growing rapidly, there are still few well-modelled life cycle assessment (LCA) studies available for quantifying their potential environmental benefits and impacts. Existing studies mainly rely on data for electric vehicles and often lack a thorough modelling approach, especially regarding the peripheral components. This paper presents a full cradle to grave LCA of a Lithium iron phosphate (LFP) battery HSS based on primary data obtained by part-to-part dismantling of an existing commercial system with a focus on the impact of the peripheral components. Additionally, alternative battery chemistries (Sodium ion battery (SIB) and two lithium nickel manganese cobalt oxides, (NMC811,and NMC622) are investigated under the consideration of the same periphery. This approach allows a comprehensive comparison between present and emerging cell chemistries that can be potentially considered for an HSS. The total greenhouse gas emissions of the HSS are 84 g CO2eq/KWh of electricity delivered over its lifetime in a residential PV application, or 31 g CO2eq/KWh over lifetime when excluding the use-phase impact. The peripheral components contribute between 37% and 85% to the total gross manufacturing impacts of the HSS, depending on the considered cell chemistry and the impact category. Especially the inverter plays an important role, and its impacts are significantly higher than those obtained when using the standard ecoinvent dataset, indicating that the contribution of power electronics might often be underestimated when using this dataset. In terms of cell chemistries, the considered SIB turns out to be not yet competitive with LIB chemistries due to its lower energy density and lifetime, but might become so when reaching similar lifetimes

Stellar Population Variations in the Milky Way's Stellar Halo

If the stellar halos of disk galaxies are built up from the disruption of dwarf galaxies, models predict highly structured variations in the stellar populations within these halos. We test this prediction by studying the ratio of blue horizontal branch stars (BHB stars; more abundant in old, metal-poor populations) to main-sequence turn-off stars (MSTO stars; a feature of all populations) in the stellar halo of the Milky Way using data from the Sloan Digital Sky Survey. We develop and apply an improved technique to select BHB stars using ugr color information alone, yielding a sample of ~9000 g<18 candidates where ~70% of them are BHB stars. We map the BHB/MSTO ratio across ~1/4 of the sky at the distance resolution permitted by the absolute magnitude distribution of MSTO stars. We find large variations of BHB/MSTO star ratio in the stellar halo. Previously identified, stream-like halo structures have distinctive BHB/MSTO ratios, indicating different ages/metallicities. Some halo features, e.g., the low-latitude structure, appear to be almost completely devoid of BHB stars, whereas other structures appear to be rich in BHB stars. The Sagittarius tidal stream shows an apparent variation in BHB/MSTO ratio along its extent, which we interpret in terms of population gradients within the progenitor dwarf galaxy. Our detection of coherent stellar population variations between different stellar halo substructures provides yet more support to cosmologically motivated models for stellar halo growth.Comment: Astronomical Journal, in press. 10 pages, 5 color figures. Much better printed in colo

Major Merging: The Way to Make a Massive, Passive Galaxy

We analyze the projected axial ratio distribution, p(b/a), of galaxies that were spectroscopically selected from the Sloan Digital Sky Survey (DR6) to have low star-formation rates. For these quiescent galaxies we find a rather abrupt change in p(b/a) at a stellar mass of ~10^{11} M_sol: at higher masses there are hardly any galaxies with b/a<0.6, implying that essentially none of them have disk-like intrinsic shapes and must be spheroidal. This transition mass is ~3-4 times higher than the threshold mass above which quiescent galaxies dominate in number over star-forming galaxies, which suggests these mass scales are unrelated. At masses lower than ~10^{11} M_sol, quiescent galaxies show a large range in axial ratios, implying a mix of bulge- and disk-dominated galaxies. Our result strongly suggests that major merging is the most important, and perhaps only relevant, evolutionary channel to produce massive (>10^{11} M_sol), quiescent galaxies, as it inevitably results in spheroids.Comment: Minor changes to match published version in ApJ Letter

Testing a prediction of the merger origin of early-type galaxies: a correlation between stellar populations and asymmetry

One of the key predictions of the merger hypothesis for the origin of early-type (elliptical and lenticular) galaxies is that tidally-induced asymmetric structure should correlate with signatures of a relatively young stellar population. Such a signature was found by Schweizer and Seitzer (1992; AJ, 104, 1039) at roughly 4sigma confidence. In this paper, we revisit this issue with a nearly ten-fold larger sample of 0.01<z<0.03 galaxies selected from the Two Micron All-Sky Survey and the Sloan Digital Sky Survey. We parameterize tidal structure using a repeatable algorithmic measure of asymmetry, and correlate this with color offset from the early-type galaxy color-magnitude relation. We recover the color offset-asymmetry correlation; furthermore, we demonstrate observationally for the first time that this effect is driven by a highly-significant trend towards younger ages at higher asymmetry values. We present a simple model for the evolution of early-type galaxies through gas-rich major and minor mergers that reproduces their observed build-up from z=1 to the present day and the distribution of present-day colors and ages. We show using this model that if both stellar populations and asymmetry were ideal `clocks' measuring the time since last major or minor gas-rich interaction, then we would expect a rather tight correlation between age and asymmetry. We suggest that the source of extra scatter is natural diversity in progenitor star formation history, gas content, and merger mass ratio, but quantitative confirmation of this conjecture will require sophisticated modeling. We conclude that the asymmetry-age correlation is in basic accord with the merger hypothesis, and indicates that an important fraction of the early-type galaxy population is affected by major or minor mergers at cosmologically-recent times.Comment: Astrophysical Journal, in press. 20 pages, 18 figure

The Structure of the Sagittarius Stellar Stream as Traced by Blue Horizontal Branch Stars

We use a sample of blue horizontal branch (BHB) stars from the Sloan Digital Sky Survey Data Release 7 to explore the structure of the tidal tails from the Sagittarius Dwarf Galaxy. We use a method yielding BHB star candidates with up to ~70% purity from photometry alone. The resulting sample has a distance precision of roughly 5% and can probe distances in excess of 100 kpc. Using this sample, we identify a possible extension to the trailing arm at distances of 60-80 kpc from the Sun with an estimated significance of at least 3.8 sigma. Current models predict that a distant `returning' segment of the debris stream should exist, but place it substantially closer to the Sun where no debris is observed in our data. Exploiting the distance precision of our tracers, we estimate the mean line-of-sight thickness of the leading arm to be ~3 kpc, and show that the two `bifurcated' branches of the debris stream differ by only 1-2 kpc in distance. With a spectroscopic very pure BHB star subsample, we estimate the velocity dispersion in the leading arm, 37 km s^-1, which is in reasonable agreement with models of Sgr disruption. We finally present a sample of high-probability Sgr BHB stars in the leading arm of Sgr, selected to have distances and velocities consistent with Sgr membership, to allow further study.Comment: Astrophysical Journal, in press. 17 pages, 15 figure

The Age Spread of Quiescent Galaxies with the NEWFIRM Medium-band Survey: Identification of the Oldest Galaxies out to z~2

With a complete, mass-selected sample of quiescent galaxies from the NEWFIRM Medium-Band Survey (NMBS), we study the stellar populations of the oldest and most massive galaxies (>10^11 Msun) to high redshift. The sample includes 570 quiescent galaxies selected based on their extinction-corrected U-V colors out to z=2.2, with accurate photometric redshifts, sigma_z/(1+z)~2%, and rest-frame colors, sigma_U-V~0.06 mag. We measure an increase in the intrinsic scatter of the rest-frame U-V colors of quiescent galaxies with redshift. This scatter in color arises from the spread in ages of the quiescent galaxies, where we see both relatively quiescent red, old galaxies and quiescent blue, younger galaxies towards higher redshift. The trends between color and age are consistent with the observed composite rest-frame spectral energy distributions (SEDs) of these galaxies. The composite SEDs of the reddest and bluest quiescent galaxies are fundamentally different, with remarkably well-defined 4000A- and Balmer-breaks, respectively. Some of the quiescent galaxies may be up to 4 times older than the average age- and up to the age of the universe, if the assumption of solar metallicity is correct. By matching the scatter predicted by models that include growth of the red sequence by the transformation of blue galaxies to the observed intrinsic scatter, the data indicate that most early-type galaxies formed their stars at high redshift with a burst of star formation prior to migrating to the red sequence. The observed U-V color evolution with redshift is weaker than passive evolution predicts; possible mechanisms to slow the color evolution include increasing amounts of dust in quiescent galaxies towards higher redshift, red mergers at z<1, and a frosting of relatively young stars from star formation at later times.Comment: 20 pages, 20 figures, accepted for publication in Ap