Dust formation in primordial Type II supernovae

We have investigated the formation of dust in the ejecta of Type II supernovae (SNe), mostly of primordial composition, to answer the question of where the first solid particles are formed in the Universe. However, we have also considered non-zero progenitor metallicity values up to Z = Z_⊙ . The calculations are based on standard nucleation theory, and the scheme has been tested for the first time on the well-studied case of SN1987A, yielding results that are in agreement with the available data. We find that: (i) the first dust grains are predominantly made of silicates, amorphous carbon (AC), magnetite and corundum; and (ii) the largest grains are the AC ones, with sizes around 300 Å, whereas the other grain types have smaller radii, around 10–20 Å . The grain size distribution depends somewhat on the thermodynamics of the ejecta expansion, and variations in the results by a factor ≈2 might occur within reasonable estimates of the relevant parameters. Also, and for the same reason, the grain size distribution is essentially unaffected by metallicity changes. The predictions on the amount of dust formed are very robust: for Z =0 , we find that SNe with masses in the range (12–35) M_⊙ produce about 0.08 M_⊙≲ M _d≲0.3 M_⊙ of dust per supernova. The above range increases by roughly three times as the metallicity is increased to solar values. We discuss the implications and the cosmological consequences of the results.     

Plate convergence measured by GPS across the Sundaland/Philippine Sea Plate deformed boundary: the Philippines and eastern Indonesia

The western boundary of the Philippine Sea (PH) Plate in the Philippines and eastern Indonesia corresponds to a wide deformation zone that includes the stretched continental margin of Sundaland, the Philippine Mobile Belt (PMB), extending from Luzon to the Molucca Sea, and a mosaic of continental blocks around the PH/Australia/Sunda triple junction. The GPS GEODYSSEA data are used to decipher the present kinematics of this complex area. In the Philippines, the overall scheme is quite simple: two opposing rotations on either side of the left-lateral Philippine Fault, clockwise to the southwest and counterclockwise to the northeast, transfer 55 per cent of the PH/Sundaland convergence from the Manila Trench to the northwest to the Philippine Trench to the southeast. Further south, 80 per cent of the PH/Sunda convergence is absorbed in the double subduction system of the Molucca Sea and less than 20 per cent along both continental margins of northern Borneo. Finally, within the triple junction area between the Sundaland, PH and Australia plates, from Sulawesi to Irian Jaya, preferential subduction of the Celebes Sea induces clockwise rotation of the Sulu block, which is escaping toward the diminishing Celebes Sea oceanic space from the eastward-advancing PH Plate. To the south, we identify an undeformed Banda block that rotates counterclockwise with respect to Australia and clockwise with respect to Sundaland. The kinematics of this block can be defined and enable us to compute the rates of southward subduction of the Banda block within the Flores Trench and of eastward convergence of the Makassar Straits with the Banda block. The analysis made in this paper confirms that this deformation is compatible with the eastward motion of Sundaland with respect to Eurasia determined by the GEODYSSEA programme but is not compatible with the assumption that Sundaland belongs to Eurasia, as was often assumed prior to this study.     

Inhomogeneous reionization of the intergalactic medium regulated by radiative and stellar feedbacks

We study the inhomogeneous reionization in a critical density CDM universe resulting from stellar sources, including Population III objects. The spatial distribution of the sources is obtained from high-resolution numerical N -body simulations. We calculate the source properties, taking into account a self-consistent treatment of both radiative (i.e. ionizing and H₂-photodissociating photons) and stellar (i.e. SN explosions) feedbacks regulated by massive stars. This allows us to describe the topology of the ionized and dissociated regions at various cosmic epochs, and to derive the evolution of H, He and H₂ filling factors, soft UV background, cosmic star formation rate and the final fate of ionizing objects. The main results are: (i) galaxies reionize the intergalactic medium by z ≈10 (with some uncertainty related to the gas clumping factor), whereas H₂ is completely dissociated already by z ≈25; (ii) reionization is mostly caused by the relatively massive objects which collapse via H line cooling, while objects the formation of which relies on H₂ cooling alone are insufficient for this purpose; (iii) the diffuse soft UV background is the major source of radiative feedback effects for z ≤15; at higher z direct flux from neighbouring objects dominates; (iv) the match of the calculated cosmic star formation history with that observed at lower redshifts suggests that the conversion efficiency of baryons into stars is ≈1 per cent; (v) we find that a very large population of dark objects which failed to form stars is present by z ≈8. We discuss and compare our results with similar previous studies.     

Gravitational lensing effects on high-redshift Type II supernova studies with the Next Generation Space Telescope

We derive the expected Type II supernova (SN) differential number counts, N ( m ), and Hubble diagram for SCDM and LCDM cosmological models, taking into account the effects of gravitational lensing (GL) produced by the intervening cosmological mass. The mass distribution of dark matter haloes (i.e. the lenses) is obtained by means of a Monte Carlo method applied to the PressSchechter mass function. The haloes are assumed to have a Navarro, Frenk & White (NFW) density profile, in agreement with recent simulations of hierarchical cosmological models. Up to z =15, the (SCDM, LCDM) models predict a total number of (857, 3656) SNII yr¹ in 100 surveyed 44 arcmin² fields of the Next Generation Space Telescope ( NGST ). NGST will be able to reach the peak of the N ( m ) curve, located at AB 30(31) for SCDM (LCDM) in J and K wavelength bands, and detect (75 per cent, 51 per cent) of the above SN events. This will allow a detailed study of the early cosmic star formation history, as traced by SNIIe. N ( m ) is only very mildly affected by the inclusion of lensing effects. In addition, GL introduces a moderate uncertainty in the determination of cosmological parameters from Hubble diagrams, when these are pushed to higher z . For example, for a 'true' LCDM with (_M=0.4, =0.6), without proper account of GL, one would instead derive We briefly compare our results with previous similar work and discuss the limitations of the model.     

Cosmic microwave background anisotropies resulting from feedback-regulated inhomogeneous reionization

We calculate the secondary anisotropies in the cosmic microwave background (CMB) produced by inhomogeneous reionization from simulations in which the effects of radiative and stellar feedback effects on galaxy formation have been included. This allows us to determine self-consistently the beginning ( z _i≈30), the duration ( δz ≈20) and the (non-linear) evolution of the reionization process for a critical density cold dark matter (CDM) model. In addition, from the simulated spatial distribution of ionized regions, we are able to calculate the evolution of the two-point ionization correlation function, C _χ , and obtain the power spectrum of the anisotropies, C _ℓ, in the range 5000<ℓ<10⁶. The power spectrum has a broad maximum around ℓ≈30 000, where it reaches the value 2×10⁻¹². We also show that the ionization correlation function C _χ is not Gaussian, but at separation angles θ ≲10⁻⁴ rad it can be approximated by a modified Lorentzian shape; at larger separations an anticorrelation signal is predicted for both C _χ and C ( θ ). Detection of signals as above will be possible with future millimetre-wavelength interferometers like the Atacama Large Millimeter Array (ALMA) , which appears as an optimum instrument to search for signatures of inhomogeneous reionization.     

The structure of the benthic macrofaunal assemblages and sediments characteristics of the Paraguaçu estuarine system, NE, Brazil

The structure of the benthic macrofaunal assemblages of the estuarine portion of Paraguaçu River, NE, Brazil, and its relationship with surface sediment characteristics (trace metals, PAHs, nutrients and grain size) and physical variables were investigated at ten stations on two contrasting occasions, summer (dry season) and winter (rainy season). A total of 1258 individuals (632 in winter and 626 in summer) and 62 taxa representing polychaetes, crustaceans, bivalves, echinoderms, bryozoans, sponges, cnidarians and cephalochordates were collected. Benthic assemblages in the upper estuary were unlike those in the lower estuary and a clear substitution of benthic taxa along the estuary was observed. Macrofaunal invertebrates in the low salinity region, composed of coarse sediments, were dominated by tellinids, venerids (bivalves), cirolanids (isopods), cyclopoids (copepods), and nereidids (polychaetes). While the high salinity region, composed of fine sediments, were dominated by nuculids (bivalves), cirratulids (polychaetes), and by amphiurids (ophiuroids). The Paraguaçu estuarine system is not severely affected by anthropogenic activities. In the great majority of the study sites, concentrations of trace metals and PAHs in the sediments were near background values. Nutrients values were also low. We formulated new models of taxon distribution and suggested detailed studies on the effects of salinity variation and studies using functional approaches to better understand the processes causing the spatial patterns in tropical estuarine benthic assemblages.     

Quiescent times in gamma-ray bursts – II. Dormant periods in the central engine?

Within the framework of the internal–external shocks model for γ -ray bursts, we study the various mechanisms that can give rise to quiescent times in the observed γ -ray light curves. In particular, we look for the signatures that can provide us with evidence as to whether or not the central engine goes dormant for a period of time comparable to the duration of the gaps. We show that the properties of the prompt γ -ray and X-ray emission can, in principle, determine whether the quiescent episodes are caused by a modulated relativistic wind or a switching off of the central engine. We suggest that detailed observations of the prompt afterglow emission from the reverse shock will strongly constrain the possible mechanisms for the production of quiescent times in γ -ray bursts.