Gravitational Lensing at Millimeter Wavelengths

With today's millimeter and submillimeter instruments observers use gravitational lensing mostly as a tool to boost the sensitivity when observing distant objects. This is evident through the dominance of gravitationally lensed objects among those detected in CO rotational lines at z>1. It is also evident in the use of lensing magnification by galaxy clusters in order to reach faint submm/mm continuum sources. There are, however, a few cases where millimeter lines have been directly involved in understanding lensing configurations. Future mm/submm instruments, such as the ALMA interferometer, will have both the sensitivity and the angular resolution to allow detailed observations of gravitational lenses. The almost constant sensitivity to dust emission over the redshift range z=1-10 means that the likelihood for strong lensing of dust continuum sources is much higher than for optically selected sources. A large number of new strong lenses are therefore likely to be discovered with ALMA, allowing a direct assessment of cosmological parameters through lens statistics. Combined with an angular resolution <0.1", ALMA will also be efficient for probing the gravitational potential of galaxy clusters, where we will be able to study both the sources and the lenses themselves, free of obscuration and extinction corrections, derive rotation curves for the lenses, their orientation and, thus, greatly constrain lens models.Comment: 69 pages, Review on quasar lensing. Part of a LNP Topical Volume on "Dark matter and gravitational lensing", eds. F. Courbin, D. Minniti. To be published by Springer-Verlag 2002. Paper with full resolution figures can be found at ftp://oden.oso.chalmers.se/pub/tommy/mmviews.ps.g

Molecular phylogeny of viviparous Australian elapid snakes: Affinities of Echiopsis atriceps (Storr, 1980) and Drysdalia coronata (Schlegel, 1837), with description of a new genus

The rare Australian venomous elapid snake 'Echiopsis' atriceps has been the subject of considerable taxonomic instability with the five known specimens assigned to four genera by various authorities. Phylogenetic affinities of the rare Elapognathus minor also are poorly understood and have been the subject of some disagreement. To examine the phylogenetic affinities of these two rare taxa, a molecular data set comprising 1680 base pairs of mtDNA was assembled from a representative of each of the terrestrial Australian viviparous elapid genera and two species of Drysdalia, a genus about which there also has been phylogenetic controversy. A total of 936 base pairs of 12S rRNA, 454 base pairs of 16S rRNA and 290 base pairs of cytochrome b mtDNA were sequenced for 15 species. The Asian elapid Naja naja was used as the outgroup. These mtDNA regions provided 195, 38 and 72 parsimony informative sites, respectively, for a total of 315 parsimony informative characters. Unweighted phylogenetic analyses were performed under both parsimony and neighbour-joining criteria. Parsimony analyses of the unweighted, combined data set resulted in a single fully resolved most parsimonious tree 1225 steps long. The neighbour-joining tree differed by only a single weakly supported branch. These data strongly support a sister group relationship between 'Echiopsis' atriceps and the Australian broadheaded snakes of the genus Hoplocephalus with a bootstrap value of 99%. Templeton tests soundly reject all previous taxonomic arrangements for this species. Our data also strongly support a sister group relationship between Elapognathus minor and Drysdalia coronata with a bootstrap value of 98%. Importantly, Drysdalia coronata and Drysdalia coronoides do not form a monophyletic group, supporting some previous studies. Based on our results, we allocate 'Echiopsis' atriceps to a new monotypic genus and re-describe Elapognathus to include 'Drysdalia' coronata