Change of pace - a revisit of two bright and intriguing galaxies with some interesting details.
NGC 7479, the Superman Galaxy – disturbed barred Seyfert in Pegasus:
I’m a little surprised this one is not in Arp’s atlas, as one arm certainly appears dominant. 7479 is a very active Seyfert galaxy showing star formation in nearly every structure – from the arms to right across the bar, including the nucleus. The starburst activity is attributed to a merger with a dwarf galaxy around 100 million years ago. The so-called “Superman” galaxy sits at a distance of 105 million ly.
Observing: This observation was one of two revisits during the session. NGC 7479 was seen 2 years ago using medium magnification (235x) under conditions that were not quite as good with both transparency and seeing were recorded at 3/5. I wasn’t using the sky meter at the time, but this time transparency was better at 10,797 ADU and seeing much better at 1.30 a/sec. I would call that at 4-4.5/5 for transparency and 4-4.5/5 for seeing. Conditions were forecast to slowly deteriorate, so this observation was put first for the best chance of making out as much of the arms as possible, along with the HII regions.
The galaxy is bright, and its arm structure was visible at all magnifications, but best at 235x and 381x. The HII regions stood out best at 762x which also allowed a nice frame between the two prominent stars to the north and south. The sketch is a composite of those different views.
The central core and bar created a bright 3:1 oval, from which the nucleus stood out – barely. The halo showed the same aspect with greater extension and sharply tapered at the ends, not quite reaching the bright star to the south. One HII region stood out at the southern end of the bar [HBK83 (36)]. Both arms clearly bend off the ends of the bar, curling back in the opposite direction. The southern arm was clearly brighter and more distinct than the northern arm, containing 3 distinct HII knots. Two of those were right next to one another in the southernmost bend of the arm and appeared as tight round dots in the nebulous arm [RZH99 (95 & 12)]. Another [HK83(57)] appeared in the arm further along the curve due west of the nucleus. This HII was extended along the arm for a distance more than the other two and the space between them combined. The designations are taken from Alvin Huey’s Extragalactic Objects guide, p. 27. A star shone right in the center of the southern arm’s curve, like the point of the compass that drew it. Delightful. The southern arm faded out as it continued to the north, with the end of the nebulosity marked by a very faint and intermittent star.
The northern arm clearly began at the northern tip of the bar and curved first toward the bright star to the north, then east and then south, mirroring the other arm, but was much fainter and more difficult to make out directly for much of its length. Averted vision was needed to make out the whole thing, and as mentioned 235x provided the better view. This arm also curved around a star, not quite as centrally placed nor was it as bright as its partner surrounded by the southern arm. This star was intermittent and winked out during moments of better seeing.
This observation afforded more detail than two years ago. Conditions were better, I’d acquired the 2x Power Mate since then and this time knew to look for more details within the object. NGC 7479 was a delightful galaxy to observe in 2022, but even more so this time around.
Sketching: white pastel pencils and white pastel powder on Strathmore 184 lb. black multimedia paper. Most of the halo, core and bar would drawn with #6 and #2 Filbert brushes and the nucleus and HII knots with a 10/0 mini Filbert.
NGC 520 / Arp 157 – merging galaxies in Picses:
Photos of this object show the results of a cosmic trainwreck – two galaxies at the early stages of a collision that began around 300 million years ago, and still showing velocity spreads between the two merging structures. The object is around 105 million ly distant.
Observing: Conditions gradually deteriorated as the night went on but were still okay. Transparency had degraded by 1000 to 9,900 ADU, but seeing only by 0.1 a/sec, 1.47 at the time of observation. Maybe if things had held together, I would have made out more of the fascinating tidal tails. The previous observation was a year ago under slightly worse conditions, particularly the SQM reading of 19.85 as compared to 20.76. My notes don’t mention why I didn’t go for higher magnification, but perhaps things got too muddy. 762x worked fine this time.
NGC 520 was bright and presented as a 3:1 rectangular glow at first look. A line of three faint stars appeared to the southeast, aligned with the long axis. With time a dark lane divided the glow down the middle of the long axis, with the southwestern half about 50% longer than the northeastern half and somewhat brighter. Both segments showed elongated brightening towards the center, and the southwestern half had an additional bright portion at its southwestern end. The ends of both halves bent slightly away from one another. Tidal tails appeared off both ends of the object; not as extensive and convoluted as seen in photos, but it was clear something was going on.
It never ceases to amaze me that we can see things like this. At first glance the night sky seems rather static, or slow moving. But Arp 157 reminds us that nothing could be further from the truth. What a dynamic universe we live in.
Sketching: white pastel pencils and white pastel powder on Strathmore 184 lb. black multimedia paper. All Filberts for this one = #6, #2 and 10/0 mini.
Thanks for looking all! Hopefully December will afford more skies like this, or better!
-b
