CMB angular power spectrum بیناب ِ توانی ِ زاویهای ِ CMB binâb-e tavâni-ye zâviye-yi-e CMB
*Fr.: spectre de puissance angulaire du CMB*
A plot displaying the amplitude of
→ *cosmic microwave background anisotropy*
as a function of angular size or → *multipole index*.
Same as → *angular fluctuation spectrum*.
The plot, based the on WMAP and other data, shows a plateau at large angular or length
scales (→ *Sachs-Wolfe plateau*),
then a series of peaks at progressively smaller scales.
These features arise from the gravity-driven
acoustic oscillations of the coupled photon-baryon fluid in the early
Universe (→ *baryon acoustic oscillation*).
In particular, a strong peak is seen
on an angular scale (at *l* ~220), corresponding to the physical
length of the → *sound horizon* at the
→ *recombination era*.
It depends on the curvature of space. If space is
positively curved, then this sound horizon scale will appear larger on
the sky than in a flat Universe (the first peak will move to the
left). The second peak (*l* ~ 550), which is the first harmonic of the
main peak, relates to the baryon/photon ratio. The third peak can be
used to help constrain the total matter density. → *angular*; → *fluctuation*;
→ *spectrum*. |