# AGN accretion disk double peak explained?

I have a question to the following lecture: https://ned.ipac.caltech.edu/level5/Fabian4/Fab2_2.html

In Figure 3 it says that a narrow annuli of a Newtonian disk should alrdy show a double peak profile. What I don't understand is how the double peak profile formes in the newtonian case? If I imagine a non rotating narrow annuli it has a single peak only at $$E_0$$. Now when it rotates some photons will be red or blue shifted by the factors $$z_1$$, $$z_2$$, $$z_3$$, and so on (classical Doppler effect). The rotating narrow annuli is symmetric therefore the number of non shifted photons should be the same as the number of photones shifted by $$z_1$$ which is the same as number of photons shifted by $$z_2$$ and so on. So there shouldn't form a double peak profile where the flux of red or blue shifted photones by the factor $$z_x$$ is bigger than the non shifted photones? But why does a double peak profile according to the lecture form, what do I understand wrong? I would appreciate if someone could walk me trough. thx

• That diagram has two narrow annuli, as marked by the 2 dashed circles. – PM 2Ring Sep 20 at 16:59
• Thats right but it doesn't rly help me because in figure 3 upper panel the two annuli are represented by two different double peak profiles. So one annuli has still a double peak that I don't understand. – Tobias Trust Sep 20 at 17:34