Investigating the central engine of ultraluminous infrared galaxies: near-infrared imaging

We present 0.5-arcsec-resolution near-infrared images of six ultraluminous infrared galaxies with known redshifts. Six of the eight bright nuclei are resolved on kiloparsec scales, suggesting that there is significant circumnuclear star formation or close progenitor nuclei. At this spatial resolution, the nuclei have very red colours that cannot in general be reproduced by reddening stellar light, but require an additional component of hot dust emission. In five of the six primary nuclei more than 20 per cent of the K -band continuum originates in hot dust, but the temperature cannot be determined by JHK broad-band colours alone. Comparison with the spectral shapes, however, does allow the temperature to be constrained, and we find in every case that it is at the upper end of the permissible range, ≳1000 K. This does not necessarily imply that there is an active galactic nucleus present, since there is evidence that stellar processes can also generate dust this hot via stochastic heating of small grains. The quantities of hot dust we have found here can make up to 0.5-mag difference to the K -band magnitude even at     , with implications for observations and population synthesis models of higher-redshift objects. Observations in the L or M bands, where hot dust is most important at     , could help to discriminate between models of dusty starbursts and ellipticals.     

Environmental effects on galaxy properties

This is a study concerning the investigation of galaxy formation and evolution in small-scale structures and the influence of the environment on the properties of galaxies. The environment plays a key role in the evolution of galaxies since it governs the type of encounters. We present results from low-resolution spectroscopy and R-band surface photometry of multiplets of galaxies found in low-density environments and compare them to cluster environments. Properties such as induced galaxy activity, star formation enhancements, AGN activity and the connection between merging and galaxy morphology are investigated. This revised version was published online in August 2006 with corrections to the Cover Date.     

Tracing the star stream through M31 using planetary nebula kinematics

We present a possible orbit for the Southern Stream of stars in M31, which connects it to the Northern Spur. Support for this model comes from the dynamics of planetary nebulae (PNe) in the disc of M31: analysis of a new sample of 2611 PNe obtained using the Planetary Nebula Spectrograph reveals ∼20 objects with kinematics inconsistent with the normal components of the galaxy, but which lie at the right positions and velocities to connect the two photometric features via this orbit. The satellite galaxy M32 is coincident with the stream both in position and velocity, adding weight to the hypothesis that the stream comprises its tidal debris.     

Tidal disruption model for the interacting pair of galaxies VV 117 (NGC 2444/45)

A series of N-body simulations have been performed to interpret the interacting pair of galaxies VV 117 (NGC 2444/45). The galaxies have been modelled assuming a mass ratio two. The simulations use various values for the distance of closest approach and the eccentricity of the relative orbit of the pair. A plausible scenario for the tidal disruption of the less massive galaxy is proposed. NGC2444, having double the mass of NGC 2445, has undergone penetrating collision with the latter in a hyperbolic or a parabolic orbit. After the first collision, the orbit has become bound. Our results show that VV 117 has either just emerged from the first collision or are on the verge of a second collision. NGC 2445suffers considerable disruption and mass loss. NGC 2444 is not affected much. The second collision is expected to culminate in the merger of the two galaxies. This revised version was published online in July 2006 with corrections to the Cover Date.     

强作用对奇异星观测效应的影响

奇异星是类似于中子星的曲奇异夸克物质组成的致密天体。本文研究了夸克这间的强作用对奇异星观测效应的影响。我们认为：（１）中子星转变为奇异星的行为是一种大的周期突变（ｇｌｉｔｃｈ）现象，这种现象取决于夸克间的强作用；（２）强作用使高温奇异星的振动阻尼也有效，这可能是驱动超新星爆发的新机制；（３）强作用加强了高温情形下奇异星和中子星在转动上的差别，奇异星的最小周期比中子星的小。     

Ethnic coexistence in a pluralistic campus environment

In Malaysia, ethnic segregation seems to have grown more and more pronounced at all levels of education, which may have in the main contributed to increasing occupational segregation by ethnicity when the graduates left to join the job market. Such trends may be disturbing given the effort the country has put in to promote interethnic understanding and reduce interethnic economic disparity since 1970. By critically investigating the dynamics of ethnic coexistence in the microcosm of the university campus environment, this paper provides statistical evidence to show how far the country has progressed in terms of ethnic relations since the watershed events of May 13, 1969; to what extent Malaysian multiethnic society is different now compared to the unmistakable racial “corporateness” and interethnic “separateness” that Furnivall observed in his classic study of 1948; and in what ways ethnic relations have been reshaped by three decades of affirmative action policies and the form of ethnic democracy adapted for this unique society.

Recurrent daily OLR patterns in the Southern Africa/Southwest Indian Ocean region,implications for South African rainfall and teleconnections

A cluster analysis of daily outgoing longwave radiation (OLR) anomalies from 1979 to 2002 over the Southern Africa/Southwest Indian Ocean (SWIO) region for the November to February season reveals seven robust and statistically well separated recurrent patterns of large-scale organized convection. Among them are three regimes indicative of well defined tropical–temperate interactions linking the hinterland parts of Southern Africa to the mid-latitudes of the SWIO. Preferred transitions show a tendency for an eastward propagation of these systems. Analysis of daily rainfall records for South Africa shows that six of the OLR regimes are associated with spatially coherent and significant patterns of enhanced or reduced daily rainfall over the country. Atmospheric anomalies from the NCEP/DOE II reanalysis dataset show that the OLR regimes are associated with either regional or near-global adjustments of the atmospheric circulation, the three regimes representative of tropical–temperate interactions being in particular related to a well-defined wave structure encompassing the subtropical and temperate latitudes, featuring strong vertical anomalies and strong poleward export of momentum in the lee of the location of the cloud-band. The time-series of OLR regimes seasonal frequency are correlated to distinctive anomaly patterns in the global sea-surface-temperature field, among which are shown to be those corresponding to El Nino and La Nina conditions. The spatial signature of El Nino Southern Oscillation’s (ENSO) influence is related to the combination of an increased/decreased frequency of these regimes. It is shown in particular that the well-known “dipole” in convection anomalies contrasting Southern Africa and the SWIO during ENSO events arises as an effect of seasonal averaging and is therefore not valid at the synoptic scale. This study also provides a framework to better understand the observed non-linearities between ENSO and the seasonal convection and rainfall anomalies over the region.     

The changing interstellar medium of massive elliptical galaxies and cosmic evolution of radio galaxies and quasars

The recently discovered apparent dramatic expansion in the effective radii of massive elliptical galaxies from   z ≃ 2  to ≃0.1 has been interpreted in terms of either galaxy mergers or the rapid loss of cold gas due to active galactic nuclei (AGN) feedback. In examining the latter case, we have quantified the extent of the expansion, which is uncertain observationally, in terms of the star formation parameters and time of the expulsion of the cold gas. In either case, the large global decrease in stellar density should translate into a major drop in the interstellar medium density and pressure with cosmic epoch. These cosmological changes are expected to have a major influence on the gas accretion mode, which will shift from 'cold' thin disc accretion at high redshifts towards 'hot' Bondi fed Advection Dominated Accretion Flow (ADAF) accretion at low redshifts. The decline of angular momentum inflow would then lead to a spin down of the black hole, for which we have calculated more precise time-scales; a value of about 0.2 Gyr is typical for a  10⁹ M_⊙  central black hole. These results have implications for the different cosmological evolutionary patterns found for the luminosity functions of powerful and weak radio galaxies.