Arp 99 / NGC 7547, 7549, 7550

Designation(s)Arp 99, NGC 7547, NGC 7549, NGC 7550
Object Type(s)Galaxy
Relevant Catalog(s)All (Chron), Arp, NGC
Arp CategorySpiral galaxies with elliptical companions on arms
Obs. Lat/Long42° 17', 073° 57'
ConstellationPegasus
Date and Time Observed2024-10-27 20:50:00
InstrumentEdgeHD 8" w/f7 reducer-1,422mm FL
CameraPlayer One Apollo Mini
Image DetailsUp is 177.9 degrees E of N (i.e. N is down). West is 90 degrees clockwise (left). Exposures 15s@300g, UV/IR Cut Filter. Darks subtracted, no flats. Dithered and recentered in SharpCap. No guiding.
DescriptionThis is a fascinating cluster which appears to capture 3 galaxies in a dance of attraction. The elliptical galaxy NGC 7550 on the top, center (south) appears to be dominating. It seems to have unwound the spiral galaxy NGC 7549 (bottom center) into an extended S curve, and to be attracting and stretching the more intact spiral galaxy NGC 7547 (probably a circular spiral at first). That said, I inverted the image to see if I could see any dust lanes indicating exchange of mass. Pushing on stretching the inverted image as hard as I dared (see gallery), I believe there's a hint of a connection between 7547 and 7550, and likely none with 7549.. I also wonder whether NGC 7553 participates in this dance as well (and possibly 7558). They're not included in the Atlas, but I wondered if they might have been outside the FOV of the Hale Telescope, and therefore not considered. So I investigated. According to the CalTech website, image scale at 1x (lowest) magnification on the Hale Telescope was 11.1" per mm. Plates were usually 5 inches x 7 inches, converting to 178 mm, or 0.55°/33". Turns out that the angular distance from NGC 7547 (western most) to NGC 7558 (easternmost) is under 10", so the FOV was not a limiting factor.
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