How does the cosmic large-scale structure bias the Hubble diagram?

The Hubble diagram is one of the cornerstones of observational cosmology. It is usually analysed assuming that, on average, the underlying relation between magnitude and redshift matches the prediction of a Friedmann-Lema\^itre-Robertson-Walker model. However, the inhomogeneity of the Universe generically biases these observables, mainly due to peculiar velocities and gravitational lensing, in a way that depends on the notion of average used in theoretical calculations. In this article, we carefully derive the notion of average which corresponds to the observation of the Hubble diagram. We then calculate its bias at second-order in cosmological perturbations, and estimate the consequences on the inference of cosmological parameters, for various current and future surveys. We find that this bias deeply affects direct estimations of the evolution of the dark-energy equation of state. However, errors in the standard inference of cosmological parameters remain smaller than observational uncertainties, even though they reach percent level on some parameters; they reduce to sub-percent level if an optimal distance indicator is used.Comment: 19+7 pages, 10 figures, v2 accepted by JCAP; minor changes to improve clarit

Galaxy And Mass Assembly (GAMA): data release 4 and the z < 0.1 total and z < 0.08 morphological galaxy stellar mass functions

Galaxie

Benthic respiration and nitrogen release in Buzzards Bay, Massachusetts

The decomposition of organic matter and the regeneration of nitrogen in the sediments of Buzzards Bay, Massachusetts were examined by measuring benthic fluxes of oxygen and dissolved inorganic nitrogen (DIN). Benthic respiration (O2 consumption) rates measured from one site yielded an estimate of 65–80 g C m−2 oxidized annually. Comparing the annual release of DIN with the consumption of O2 led to an estimate of N loss from the benthic-pelagic system, most likely as N2 gas via denitrification, corresponding to 14–32% of the N remineralized from organic matter decomposition. Using path analysis, benthic flux rates of O2 and DIN over a seasonal cycle in Buzzards Bay were determined to be related to water temperature and sediment photosynthetic pigments (chlorophyll a and phaeopigments). The rate of DIN release was also negatively related to the particulate organic N (PON) pool as well. The relationship of benthic fluxes to sedimentary pigment concentrations suggested that pigments were good indicators of labile organic matter input to sediments. Macrofauna appeared to have a direct negative effect, as well as a positive indirect effect on DIN release. Benthic respiration rates were not related to sedimentary particulate organic C (POC) or PON content, or macrofaunal abundances. Release rates of DIN were also unrelated to POC pools. Benthic flux rates measured at 12 sites in Buzzards Bay during August 1989 varied by less than a factor of 2 for benthic respiration and less than a factor of 3 for DIN release. The only environmental factor that emerged from path analysis as related (negatively) to the spatial pattern of benthic flux rates in August was water depth. Other factors, such as organic pools, pigment concentrations, macrofauna, and distance from the New Bedford sewage outfall were not related to the spatial patterns of benthic fluxes in Buzzards Bay. The combination of seasonal and spatial observations indicate that the processes oxidizing organic matter in Buzzards Bay sediments are controlled by temperature and the delivery of labile organic matter to the sediment surface. Benthic flux rates in Buzzards Bay were generally low, but N recycling efficiency was high, relative to similar coastal environments

The fate of nitrogen and phosphorus at the land-sea margin of the North Atlantic Ocean

Five large rivers that discharge on the western North Atlantic continental shelf carry about 45% of the nitrogen (N) and 70% of the phosphorus (P) that others estimate to be the total flux of these elements from the entire North Atlantic watershed, including North, Central and South America, Europe, and Northwest Africa. We estimate that 61 · 10 9 moles y - 1 of N and 20 · 10 9 moles y -1 of P from the large rivers are buried with sediments in their deltas, and that an equal amount of N and P from the large rivers is lost to the shelf through burial of river sediments that are deposited directly on the continental slope. The effective transport of active N and P from land to the shelf through the very large rivers is thus reduced to 292 · 10 9 moles y -1 of N and 13 · 10 9 moles y -1 of P. The remaining riverine fluxes from land must pass through estuaries. An analysis of annual total N and total P budgets for various estuaries around the North Atlantic revealed that the net fractional transport of these nutrients through estuaries to the continental shelf is inversely correlated with the log mean residence time of water in the system. This is consistent with numerous observations of nutrient retention and loss in temperate lakes. Denitrification is the major process responsible for removing N in most estuaries, and the fraction of total N input that is denitrified appears to be directly proportional to the log mean water residence time. In general, we estimate that estuarine processes retain and remove 30-65% of the total N and 10-55% of the total P that would otherwise pass into the coastal ocean. The resulting transport through estuaries to the shelf amounts to 172-335 · 10 9 moles y -1 of N and 11-19 · 10 9 moles y -1 of P. These values are similar to the effective contribution from the large rivers that discharge directly on the shelf. For the North Atlantic shelf as a whole, N fluxes from major rivers and estuaries exceed atmospheric deposition by a factor of 3.5-4.7, but this varies widely among regions of the shelf. For example, on the U.S. Atlantic shelf and on the northwest European shelf, atmospheric deposition of N may exceed estuarine exports. Denitrification in shelf sediments exceeds the combined N input from land and atmosphere by a factor of 1.4-2.2. This deficit must be met by a flux of N from the deeper ocean. Burial of organic matter fixed on the shelf removes only a small fraction of the total N and P input (2-12% of N from land and atmosphere; 1-17% of P), but it may be a significant loss for P in the North Sea and some other regions. The removal of N and P in fisheries landings is very small. The gross exchange of N and P between the shelf and the open ocean is much larger than inputs from land and, for the North Atlantic shelf as a whole, it may be much larger than the N and P removed through denitrification, burial, and fisheries. Overall, the North Atlantic continental shelf appears to remove some 700-950 · 10 9 moles of N each year from the deep ocean and to transport somewhere between 18 and 30 · 10 9 moles of P to the open sea. If the N and P associated with riverine sediments deposited on the continental slope are included in the total balance, the net flux of N to the shelf is reduced by 60 · 10 9 moles y -1 and the P flux to the ocean is increased by 20 γ 10 9 moles y -1. These conclusions are quite tentative, however, because of large uncertainties in our estimates of some important terms in the shelf mass balance.SCOPUS: ar.jinfo:eu-repo/semantics/publishe