Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996mnras.278..603j&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Volume 278, Issue 2, pp. 603-610.
Astronomy and Astrophysics
Astronomy
18
Cosmology: Observations, Cosmology: Theory, Dark Matter, Distance Scale, Gravitational Lensing
Scientific paper
Universes with two degrees of freedom (Omega_0 and Lambda_0) are examined in the light of Kellerman's compilation of angular-size/redshift data for ultracompact radio sources. We find that low-density (Omega_0~0.2) models which are violently decelerating and have a large negative cosmological constant (q_0~-Lambda_0~3) fit the data very well, as well as the canonical cold dark matter (CDM) universe, and very much better than the spatially flat accelerating case; if Omega_0<=0.2, then 95 per cent confidence limits are -3.8<=Lambda_0<=-1.1, the lower limit being fixed by H_0t_0>=0.56. The significant qualitative feature of the theta-z curve in this context is asymptotic flatness (in the limit Omega_0-->0, Lambda_0≠0), rather than a pronounced minimum angular size. We give a mathematically rigorous argument, based upon the focusing of congruences of null geodesics, which shows that this feature is a singular property of vacuum-dominated universes.
Dodgson Marina
Jackson Jeffrey C.
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