Search

We present APEX (Atacama Pathfinder Experiment)-LABOCA (Large Apex Bolometer Camera) 870-μm observations of the fields surrounding the nine brightest, high-redshift, unlensed objects discovered in the South Pole Telescope’s 2500 square deg² survey. Initially seen as point sources by SPT’s 1-arcmin beam, the 19-arcsec resolution of our new data enables us to deblend these objects and search for submillimetre sources in the surrounding fields. We found 98 sources above a threshold of 3.7σ in the observed area of 1300 arcmin², where the bright central cores resolve into multiple components. After applying a radial cut to our LABOCA sources to achieve uniform sensitivity and angular size across each of the nine fields, we compute the cumulative and differential number counts and compare them to estimates of the background, finding a significant overdensity of δ ≈ 10 at S870 = 14 mJy. The large overdensities of bright submm sources surrounding these fields suggest that they could be candidate protoclusters undergoing massive star-formation events. Photometric and spectroscopic redshifts of the unlensed central objects range from z=3 to 7, implying a volume density of star-forming protoclusters of approximately 0.1Gpc⁻³. If the surrounding submm sources in these fields are at the same redshifts as the central objects, then the total star-formation rates of these candidate protoclusters reach 10,000 M⊙yr⁻¹, making them much more active at these redshifts than seen so far in either simulations or observations.

Bentonite clay washed with 6 M nitric acid is active in the oxidation of benzaldehyde to benzoic acid. There is only one product, in addition to small amounts of carbonaceous material. The reactive species is believed to be nitrate ions present in the interlamellar species, together with an interlamellar acidic aluminium species which is useful in maintaining the crystallinity of the acid-washed clay. The reaction is possible when free 6 M acid is introduced into the reaction mixture together with untreated clay, but in that case more carbonaceous material is formed. There is evidence that acid treatment leads to the introduction of acidic aluminium species in the interlamellar region which may act as pillars; these are removed on washing.