Astronomy and Astrophysics – Astrophysics
Scientific paper
2007-05-13
Mon.Not.Roy.Astron.Soc.394:438-442,2009
Astronomy and Astrophysics
Astrophysics
17 Pages, 1 Figure
Scientific paper
10.1111/j.1365-2966.2008.14321.x
The plethora of recent cosmologically relevant data has indicated that our universe is very well fit by a standard Friedmann-Lema\^{i}tre-Robertson-Walker (FLRW) model, with $\Omega_{M} \approx 0.27$ and $\Omega_{\Lambda} \approx 0.73$ -- or, more generally, by nearly flat FLRW models with parameters close to these values. Additional independent cosmological information, particularly the maximum of the angular-diameter (observer-area) distance and the redshift at which it occurs, would improve and confirm these results, once sufficient precise Supernovae Ia data in the range $1.5 < z < 1.8$ become available. We obtain characteristic FLRW closed functional forms for $C = C(z)$ and $\hat{M}_0 = \hat{M}_0(z)$, the angular-diameter distance and the density per source counted, respectively, when $\Lambda \neq 0$, analogous to those we have for $\Lambda = 0$. More importantly, we verify that for flat FLRW models $z_{max}$ -- as is already known but rarely recognized -- the redshift of $C_{max}$, the maximum of the angular-diameter-distance, uniquely gives $\Omega_{\Lambda}$, the amount of vacuum energy in the universe, independently of $H_0$, the Hubble parameter. For non-flat models determination of both $z_{max}$ and $C_{max}$ gives both $\Omega_{\Lambda}$ and $\Omega_M$, the amount of matter in the universe, as long as we know $H_0$ independently. Finally, determination of $C_{max}$ automatically gives a very simple observational criterion for whether or not the universe is flat -- presuming that it is FLRW.
Araujo Marcelo E.
Stoeger William R.
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