ABSTRACT
Quasars are the visible signatures of gas falling into the deep potential well of super-massive black holes in the centres of distant galaxies. It has been suggested that quasars are formed when two massive galaxies collide and merge, leading to the prediction that quasars should be found in the centres of regions of largest overdensity in the early Universe. In dark matter (DM)-dominated models of the early Universe, massive DM halos are predicted to attract the surrounding gas, which falls towards their centres. The neutral gas is not detectable in emission by itself, but gas falling into the ionizing cone of such a quasar will glow in the Lyman-alpha line of hydrogen, effectively imaging the DM halo. Here we present a Lyalpha image of a DM halo at redshift z = 3, along with a two-dimensional spectrum of the gaseous halo. Our observations are best understood in the context of the standard model for DM haloes; we infer a mass of (2 - 7) x 10(12) solar masses (M(\circ)) for the halo.
ABSTRACT
Over the past five years evidence has mounted that long-duration (>2 s) gamma-ray bursts (GRBs)-the most luminous of all astronomical explosions-signal the collapse of massive stars in our Universe. This evidence was originally based on the probable association of one unusual GRB with a supernova, but now includes the association of GRBs with regions of massive star formation in distant galaxies, the appearance of supernova-like 'bumps' in the optical afterglow light curves of several bursts and lines of freshly synthesized elements in the spectra of a few X-ray afterglows. These observations support, but do not yet conclusively demonstrate, the idea that long-duration GRBs are associated with the deaths of massive stars, presumably arising from core collapse. Here we report evidence that a very energetic supernova (a hypernova) was temporally and spatially coincident with a GRB at redshift z = 0.1685. The timing of the supernova indicates that it exploded within a few days of the GRB, strongly suggesting that core-collapse events can give rise to GRBs, thereby favouring the 'collapsar' model.
ABSTRACT
The influence of potassium, in the submonolayer regime, on the adsorption and coadsorption of CO2 and H on a stepped copper surface, Cu(115), has been studied by photoelectron spectroscopy, temperature-programmed desorption, and work-function measurements. Based on the fast recording of C 1s and O 1s core-level spectra, the uptake of CO2 on K/Cu(115) surfaces at 120 K has been followed in real time, and the different reaction products have been identified. The K 2p3/2 peak exhibits a chemical shift of -0.4 eV with CO2 saturation, the C 1s peaks of the CO3 and the CO species show shifts of -0.8 and -0.5 eV, respectively, and the C 1s peak of the physisorbed CO2 exhibits no shift. The effects of gradually heating the CO2/K/Cu(115) surface include the desorption of physisorbed CO2 at 143 K; the desorption of CO at 193 K; the ordering of the CO3 species, and subsequently the dissociation of the carbonate with desorption at 520-700 K. Formate, HCOO-, was synthesized by the coadsorption of H and CO2 on the K/Cu(115) surface at 125 K. Formate formed exclusively for potassium coverages of less than 0.4 monolayer, whereas both formate and carbonate were formed at higher coverages. The desorption of formate-derived CO2 took place in the temperature range 410-425 K and carbonate-derived CO2 desorbed at 645-660 K, depending on the potassium coverage.
