1. Yes, there are units on the vertical axis
2. There is no horizontal axis
Q: why no mergers over 80 solar masses detected?
- presumably the detection drops off as the masses get smaller. But why no larger mergers!
There are numbers on the vertical axis, not units. The units have to be inferred from the title - That’s a no-no in a good graph.
Your point on lack of detection of mergers over 80 solar masses is interesting. There either haven’t been any, or maybe they can’t be detected with the measurements. I suspect the latter, though it’s certainly not intuitive. One would think that the larger the merger, the greater the likelihood of detection. On the other hand, though, with the size of the universe as it is, one would also think that the presence of gravitational waves would be quite ‘noisy’. Maybe we’re missing something in the measurements.