Can the unresolved X-ray background be explained by the emission from the optically-detected faint galaxies of the GOODS project?

The emission from individual X-ray sources in the Chandra Deep Fields and XMM – Newton Lockman Hole shows that almost half of the hard X-ray background above 6 keV is unresolved and implies the existence of a missing population of heavily obscured active galactic nuclei (AGN). We have stacked the 0.5–8 keV X-ray emission from optical sources in the Great Observatories Origins Deep Survey (GOODS; which covers the Chandra Deep Fields) to determine whether these galaxies, which are individually undetected in X-rays, are hosting the hypothesized missing AGN. In the 0.5–6 keV energy range, the stacked-source emission corresponds to the remaining 10–20 per cent of the total background – the fraction that has not been resolved by Chandra . The spectrum of the stacked emission is consistent with starburst activity or weak AGN emission. In the 6–8 keV band, we find that upper limits to the stacked X-ray intensity from the GOODS galaxies are consistent with the ∼40 per cent of the total background that remains unresolved, but further selection refinement is required to identify the X-ray sources and confirm their contribution.     

A late pleistocene marine molluscan fauna from the Drifts of the Cheshire plain

Some recent finds from two working pits in the outwash sands of the Cheshire Plain are recorded. The opportunity is taken to discuss the dating and ecology of the fauna in relation to past and present theories of environment in the late Pleistocene, and their relationship to the fauna of the Macclesfield New Cemetery Beds.     

The environmental significance of the trace fossil Rhizocorallium jenense in the Lower Triassic of western Spitsbergen

The 500 m thick Lower Triassic succession of western comprises two shale-dominated formations, which both show upward-coarsening motifs. These reflect repeated coastal basin dominated by low energy fine-clastic sediments. The track fossils Rhizocorallium jenense and Skolithos are found in the coarser part of these units and variations in size and orientation of R. jenense give important palaeoenvironmental information.
Rhizocorallium jenense occurs in storm-generated siltstones and stones, whose deposition interrupted prevailing intermediate energy levels. Size variations and trace fossil abundance suggest an optimal habitat in the shoreface zone, with poorer adaptation to both offshore and shallower environments. Age-equivalent marine sediments on north-eastern Greenland also contain local abundant occurrences Rhizocorallium . These Arctic occurrences contrast with the same trace fossil's distribution in the Jurassic of Britain and France, where it characterizes shallower and higher energy environments; such sequences on Spitsbergen show an ichnofauna dominated by Skolithos and bivalve escape shafts.
Orientations shown by the R. jenense U-tubes show a generally, but not solely, unimodal distribution, with the curved distal entedusually oriented toward onshore. Presumed aperture lineations show strongly unimodal trends, probably related to longshore currents. Burrows in bed at the top of individual storm lobe units show more complex ably patterns probably reflecting both current and wave reworking following lobe abandonment. All finds suggest early colonization by the burrowing organisms. These were not followed by other burrowers, either because of the nutrient-poor nature of the sediment or because of high sedimentation rates.