A Peculiar Galaxy, an interesting Target for Big Telescopes, Resides in the Far Southern Skies
As a visual observer, galaxy morphology has always been a very exciting topic for me. To observe different kinds of galaxies, from the classic elliptical and spiral ones to those in groups and clusters showing peculiar shapes is something very interesting, especially if you have a chance to use a big telescope that allows you to detect the fainter and finer details of them. Among the peculiar members in the world of the galaxy morphology, we have the so-called annular galaxies or ring galaxies. As James L. Higdon et al. state in their paper "Why Are Ring Galaxies Interesting?" (2010), these objects are formed by the near central passage of a companion through a spiral along the rotation axis. The brief additional gravitational force induces epicyclic motions throughout the disk, which act to form radially propagating orbit-crowded rings of gas and stars. On other of their papers, James L. Higdon et al. argue that ring galaxies are striking examples of the ability of collisions to transform both the morphology and star-forming activity of a spiral galaxy. Numerical studies since the mid-1970s argue persuasively that the optically prominent rings are in fact outwardly propagating zones of strong orbit crowding within the disk of a spiral induced by the near central passage of a companion galaxy ("Wheels of Fire. IV. Star Formation and the Neutral Interestellar Medium in the Ring Galaxy AM1 0644-741" 2011).
If you are observing in the Southern Hemisphere during the summer season take a look, for a moment, to the Large Magellanic Cloud. It is a must-to-see object because of its size, brightness, and remarkable structure. Well, now aim your eyes about 8 degrees southeast of that galaxy. In that region of the sky, more specifically in constellation Volans, an interesting annular galaxy resides, 300 million light-years away. I´m talking about PGC 19481, also known as Graham A, the Southern Ellipse, AM 0644-7411 (Arp & Madore 1987), or Lindsay-Shapley Ring.
A way to find this peculiar galaxy is to look for the 5.1 magnitude star alpha Mensae, one of the stars that are part of the inconspicuous constellation Mensa. The galaxy lies about 2.1 degrees east-northeast of it. The J2000 coordinates of the nucleus of this galaxy are R.A. 06h43m06.s18 Dec. −74◦14 10".7.
The Lindsay-Shapley ring galaxy (AM 0644-741) appears in Category 6 of the Arp Madore catalog of Southern Peculiar Galaxies and Associations, a category that includes any galaxy with an apparent luminous ring around it, and attempts to exclude objects which appear to be spiral galaxies which have had their arms tightly wound into nearly circular appearance.
Below, there is a short video by Chandra Observatory about this enigmatic object in the Southern Sky,
"In AM 0644 741, we see a strong ring of bright blue stars in the Cerro Tololo Inter-American Observatory (CTIO) and Hubble Space Telescope (HST ) images, with associated HII regions. Unlike the Cartwheel, which shows spokes and is presumed to be a second ring-formation event (Struck-Marcell & Higdon 1993), AM 0644-741 is likely to be the first ring formed" (see the paper "Dynamical Parameters for AM 0644 741" Alex Antunes and John Wallin (2007).
As can be read on the paper "Morphology and enhanced star formation in a Cartwheel-like ring galaxy", F. Renaud et al. 2017), the Lindsay-Shapley Ring galaxy also displays an enhanced star formation activity in the furthest quadrant of its ring to the nuclei (Higdon et al. 2011).
The picture at the top of this article shows the 24-inch (0.61 meters) used to observe this galaxy. It was set up in a good field in the ranger station at the nature reserve named "Altos Limpios". You need to drive for almost 2 hours northeast from Mendoza City, in Argentina, to reach it. It is important to say that I saw this galaxy when it was about 32 degrees high in the sky (it reaches 48 degrees at its highest) and seeing was not the best that night, so maybe better results regarding the structures seen in this galaxy can be achieved with better-seeing conditions and with the galaxy at higher altitude.
The galaxy was searched, at the beginning of the observation, using 98x. After several minutes scanning the area the target was found, appearing, at this magnification, as a subtle nebulosity close to a quasi-stellar hazy spot when observing with averted vision, which is, actually, the core of the galaxy. The ring diameter, in arcsec, is 85 x 49. An asterism formed by 4 stars of magnitudes between 12 and 12.9 for those labeled in Figure 1, and magnitude 14.5 for the fourth one in the asterism labeled with a blue circle, was useful to confirm that the area was the correct (see Figure 1). A star indicated with a black arrow in Figure 1, is visible close to the galaxy´s nucleus.
The Lindsay-Shapley Ring galaxy seems to be a member, according to the SIMBAD Database, of a small group of galaxies. The two nearest galaxies (at least in projection on the sky) were also detected through the 24-inch telescope. I´m talking about the galaxies LEDA2 19455, situated about 1.2 arcmin southeast of the target galaxy, and LEDA 19454, 1.05 arcmin to the north- northeast (see Figure 2). The first one, a distorted elliptical, was visible using averted vision as a small hazy patch. Both Graham (1974) and Few, Madore, and Arp noted an extended and low surface brightness light distribution between the ring galaxy and LEDA 19455. Partly on the basis of this emission, these researchers concluded that LEDA 19455 was the intruder galaxy. The other companion, fainter, was hardly visible using also averted vision.
Applying a little higher magnification (i.e. 122x), the view was similar to that one at lower magnification. However, the nucleus of the galaxy seems to be a little easier to see, like a faint defocused star. The outer part of the galaxy, including of course the ring structure, shows up when averted vision is applied, appearing as a slightly elongated nebulosity. It is not easy to see, and the beautiful structure seen in those detailed and colorful pictures provided by ground-based telescopes and the Hubble Space Telescope is not detected. The view is rather blurry and faint. The nearby galaxies are again visible, looking faint. LEDA 19455 appears similar to the nucleus of Lindsay-Shapley Ring galaxy, both in size and brightness.
203x is a good magnification to observe the group of galaxies. LEDA 19455 looks now brighter and its presence there is undoubtful, showing a round shape. The LEDA 19454 galaxy is fainter, as said before, but it can be detected. The central part of Lindsay-Shapley Ring galaxy looks bigger and its brightness seems to be smooth. When the galaxy is observed with averted vision, an arc-shaped structure of very faint nebulosity is visible just south of the nucleus
The view of the galaxy is interesting at 244x. The nucleus is easily visible through this instrument. The whole galaxy looks like a rather elongated nebulosity, a ghostly nebulosity among the surrounding stars in the field of view of the telescope. At this power and observing more carefully, some of the structure, very faint, and indicated with an arrow in Figure 2, seems to be detected for moments. AM 0644-741 possesses twin interlocked rings, each with slightly different centers, position angles, and ellipticity. The double-ring structure makes AM 0644-741 unique among ring galaxies, much like the Cartwheel and its network of spokes. A total of 54 H II complexes were identified in the rings using Figure 2a of the paper "Wheels of Fire. III. Massive Star Formation in the "Double-Ringed" Ring Galaxy AM 0644-741" by James L. Higdon & John F. Wallin (1997). I think the slightly brighter portion visible there, barely visible even with averted vision, are some of the HII regions present in the galaxy. The authors of the mentioned paper state that the most luminous H II complexes tend to be found near the intersection of the A-ring and B-ring (see Figure 3 here) which occurs in an area of the galaxy coincident with the one I observed, indicated with the arrow in Figure 2.
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The 24-inch telescope at the "Altos Limpios" Nature Reserve.
Photo by the author.
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A way to find this peculiar galaxy is to look for the 5.1 magnitude star alpha Mensae, one of the stars that are part of the inconspicuous constellation Mensa. The galaxy lies about 2.1 degrees east-northeast of it. The J2000 coordinates of the nucleus of this galaxy are R.A. 06h43m06.s18 Dec. −74◦14 10".7.
The Lindsay-Shapley ring galaxy (AM 0644-741) appears in Category 6 of the Arp Madore catalog of Southern Peculiar Galaxies and Associations, a category that includes any galaxy with an apparent luminous ring around it, and attempts to exclude objects which appear to be spiral galaxies which have had their arms tightly wound into nearly circular appearance.
Below, there is a short video by Chandra Observatory about this enigmatic object in the Southern Sky,
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| Figure 1. Field of view of the Lindsay-Shapley Ring galaxy. |
As can be read on the paper "Morphology and enhanced star formation in a Cartwheel-like ring galaxy", F. Renaud et al. 2017), the Lindsay-Shapley Ring galaxy also displays an enhanced star formation activity in the furthest quadrant of its ring to the nuclei (Higdon et al. 2011).
The picture at the top of this article shows the 24-inch (0.61 meters) used to observe this galaxy. It was set up in a good field in the ranger station at the nature reserve named "Altos Limpios". You need to drive for almost 2 hours northeast from Mendoza City, in Argentina, to reach it. It is important to say that I saw this galaxy when it was about 32 degrees high in the sky (it reaches 48 degrees at its highest) and seeing was not the best that night, so maybe better results regarding the structures seen in this galaxy can be achieved with better-seeing conditions and with the galaxy at higher altitude.
The galaxy was searched, at the beginning of the observation, using 98x. After several minutes scanning the area the target was found, appearing, at this magnification, as a subtle nebulosity close to a quasi-stellar hazy spot when observing with averted vision, which is, actually, the core of the galaxy. The ring diameter, in arcsec, is 85 x 49. An asterism formed by 4 stars of magnitudes between 12 and 12.9 for those labeled in Figure 1, and magnitude 14.5 for the fourth one in the asterism labeled with a blue circle, was useful to confirm that the area was the correct (see Figure 1). A star indicated with a black arrow in Figure 1, is visible close to the galaxy´s nucleus.
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Figure 2. DSS image of the Lindsay-Shapley Ring galaxy and its
companions.
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Applying a little higher magnification (i.e. 122x), the view was similar to that one at lower magnification. However, the nucleus of the galaxy seems to be a little easier to see, like a faint defocused star. The outer part of the galaxy, including of course the ring structure, shows up when averted vision is applied, appearing as a slightly elongated nebulosity. It is not easy to see, and the beautiful structure seen in those detailed and colorful pictures provided by ground-based telescopes and the Hubble Space Telescope is not detected. The view is rather blurry and faint. The nearby galaxies are again visible, looking faint. LEDA 19455 appears similar to the nucleus of Lindsay-Shapley Ring galaxy, both in size and brightness.
203x is a good magnification to observe the group of galaxies. LEDA 19455 looks now brighter and its presence there is undoubtful, showing a round shape. The LEDA 19454 galaxy is fainter, as said before, but it can be detected. The central part of Lindsay-Shapley Ring galaxy looks bigger and its brightness seems to be smooth. When the galaxy is observed with averted vision, an arc-shaped structure of very faint nebulosity is visible just south of the nucleus
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Figure 3. Picture credit of James L. Higdon and John F.
Wallin, appearing as Fig 2 in their paper "Wheels of
Fire. III. Massive Star Formation in the "Double-Ringed"
ring galaxy AM 0644-741".
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In the SIMBAD Database web page, two x-ray sources are indicated as present in that area also (i.e. [WFM2018] AM0644x1, and [WFM2018] AM0644x2.).
A long time ago, something amazing happened in this distant galaxy, and you can be a witness of that when observing it from a dark sky site.
1 _ Catalogue of Southern Peculiar Galaxies and Associations (Arp, Madore): 6,445 peculiar and interacting galaxies found on IIIa-J southern sky survey plates, types, positions, and characteristic sizes, cross-identifications and selected photographs.
2 _ (Lyon-Meudon Extragalactic Database). Extension of PGC catalog in the Lyon-Meudon Extragalactic Database 1989: Catalogue of principal galaxies, 1ST edition: N=73197.
The first designation was PGC, but PGC and LEDA are now equivalent.
2 _ (Lyon-Meudon Extragalactic Database). Extension of PGC catalog in the Lyon-Meudon Extragalactic Database 1989: Catalogue of principal galaxies, 1ST edition: N=73197.
The first designation was PGC, but PGC and LEDA are now equivalent.
