Hello Christian, hello Robin,
thanks for your comments - as you mentioned, the H-Alpha emission line analysis is not a simple task.
And, I have to apologize for being very short in my first posting. So please let me summarize what I have done, and I will also describe my findings that guided me in my analysis:
1. I started with my "standard extragalactic-emission lines" spreadsheet. Here I use the typical lines Hb-[OIII], the [NII]-Ha and the [SII] - as you can see, this is my standard approach I have used in all of my postings, which positive results, so this method is "stable"
2. For M87, I have done this, too - so I have focused on the Ha-structure and tried to match it to the [NII]-Ha-[NII] "triplet". The result was negative, as the wavelength shifts and the derived redshift velocities do not fit at all to the M87 distance being a cD-galaxy in the Virgo cluster.
3. For the Virgo cluster, there is a lot of literature and lots of measurement, i.e. the velocity dispersion is well known, and the velocity amplitude's difference of more than 900km/s do not fit all either - so I concluded that the [NII]-Ha-[NII] approach cannot be used here to explain the peaks sitting "on" the broadened lines composite (see point #6).
4. Also, please note, that even if there would be an [NII] emission, this emission would also have to be structured, as the emission would also be dominated by the rotating disk. For me, this was the point where I have given up the [NII]-Ha-[NII] idea, finally.
5. Then I reviewed some M87 papers, focus on M87 emission line analysis, and a HST FOC/S showed exactly the Ha-line structure that I have also measured.
This is a similar link - showing the same disk-based-structuring force for the [OIII] line
https://www.researchgate.net/publicatio ... Gas_in_M87
(I will add the specific paper's link, I haven't it available now (I am travelling with my mobile..))
6. With the model of using a rotating disk and a complex Ha-line structure, my results yielded a velocity estimate that fits significantly good. Please note, that I also think that there is definitely also an [NII] emission, but in the M87 disk emission, the Ha-disk emission part is the dominating one, and especially the fast rotating parts of the disks are the main contributors to the Ha-emission line.
Finally, using the emission line measurements and the findings of other, more elaborate, work on the Ha-disk-emission structure, I would conclude that my data analysis is in alignment with a rotating disk in M87.
And please let me add - as a consoling and soothing remark: M87 is an active galaxy, but regarding the optical emission, a "more normal" active galaxy, i.e. Seyfert galaxies, their spectroscopical characteristic is easier to understand. Furthermore, there will be surely a "wave of M87 papers" that will be published, pushed by the latest M87 black hole press release, so it is easier to get money for future astronomical work
14"-Hypergraph, Spektrographen: Dados & LISA