MeerKAT

Abstract:

Motivated by recent results on the location of the radio emission in pulsar magnetospheres, we have developed a model which can account for the large diversity found in the average profile shapes of pulsars. At the centre of our model lies the idea that radio emission at a particular frequency arises from a wide range of altitudes above the surface of the star and that it is confined to a region close to the last open field lines. We assert that the radial height range over which emission occurs is responsible for the complex average pulse shapes rather than the transverse (longitudinal) range proposed in most current models. By implementing an abrupt change in the height range to discriminate between young, short-period, highly-energetic pulsars and their older counterparts, we obtain the observed transition between the simple and complex average pulse profiles observed in each group respectively. Monte Carlo simulations are used to demonstrate the match of our model to real observations.

Abstract:

High redshift galaxies play a key role in our developing understanding of galaxy formation and evolution. Since such galaxies are being studied within a Gyr of the big bang, they provide a unique probe of the physics of one of the first generations of large-scale star-formation. We have performed a complete statistical study of the physical properties of a robust sample of z∼5 UV luminous galaxies selected using the Lyman-break technique. The characteristic properties of this sample differ from LBGs at z∼3 of comparable luminosity in that they are a factor of ten less massive (∼few10⁹ M) and the majority (∼70%) are considerably younger (<100Myr). Our results support no more than a modest decline in the global star formation rate density at high redshifts and suggest that ∼1% of the stellar mass density of the universe had already assembled at z∼5. The constraint derived for the latter is affected by their young ages and short duty cycles which imply existing z∼5 LBG samples may be highly incomplete. These intense starbursts have high unobscured star formation rate surface densities (∼100s M yr¹ kpc²), suggesting they drive outflows and winds that enrich the intra- and inter-galactic media with metals. These properties imply that the majority of z∼5 LBGs are in formation meaning that most of their star-formation has likely occurred during the last few crossing times. They are experiencing their first (few) generations of large-scale star formation and are accumulating their first significant stellar mass. As such, z∼5 LBGs are the likely progenitors of the spheroidal components of present-day massive galaxies (supported by their high stellar mass surface densities and their core phase-space densities). © 2008 International Astronomical Union.