« Does Gravitational Lensing Affect the Cosmological Distance Redshift Relation? » |
Nick Kaiser |
A long standing question in cosmology is whether gravitational lensing changes the mean distance-redshift relation D(z) or the mean flux density of sources. In this talk I will first review the history of this subject. The problem was first considered by Jacob Zel'dovich in the early '60s and revisited by many other since. Yet the situation remains
confused. Steven Weinberg, for example, argued in '76 that there is no effect on the grounds of flux conservation, yet that seems in conflict with other calculations. Interest in this topic has been rekindled by recent results from 2nd order relativistic perturbation theory which, if correct, this would have profound implications for both supernova and CMB cosmology. In a recent submission, John Peacock and I have revisited this. In our paper we make two main points: First, we argue, expanding on Kibble and Lieu, that many of the apparent contradictions and recent claims large effects arise simply from confusion between different types of averaging (specifically between averaging over sources and averaging over directions on the sky). We then show via direct calculations that the implicit assumption of Weinberg - that the area of a surface of constant source redshift is unperturbed by lensing - is not exact, but good to about one part in a million. This effectively validates the conventional approach to CMB analysis and provides a firm basis for SN1a cosmology. |
vendredi 5 juin 2015 - 11:00 Amphithéâtre Henri Mineur, Institut d'Astrophysique de Paris |
Page web du séminaire / Seminar's webpage |