NGC 5566 in Virgo

May 2021 - Galaxy of the Month

This month’s GOM is the triple system associated with NGC 5566, also known as Arp 286. The galaxies lie in the far east of Virgo. The system is composed of the galaxies NGC 5566, 5560 and 5569.

NGC 5560 and NGC 5566 were discovered by William Herschel in 1786 but the much fainter galaxy NGC 5569 had to wait until 1849 when it was discovered by Johnstone Stoney using the 72” at Birr. Dreyer in 1878 also noted the faint galaxy now catalogued as CGCG 047-019 and sketched it while he was examining the NGC 5566 field but did not manage to get an accurate position for it so it never made it into the NGC.

The three NGC galaxies appear to form a physical triplet. All three galaxies appear to be spirals. Arp classified NGC 5566 in his group of double galaxies, infall and attraction, connection not visible. The triplet is also included in the WBL catalogue as number 501 and in the LGG as number 379. The former only includes the triplet but the LGG catalogue has 6 galaxies in LGG 379 and includes the triplet composing of NGC 5574, NGC 5576 and NGC 5577 about 41’ south as part of the group.

The NGC 5566 group appears to be interacting from the distortions in the spiral arms of NGC 5560 and also all three galaxies have strong UV emission as noted by the GALEX satellite, which suggests lots of star formation going on. NGC 5566 is particularly interesting as it appears to have a strong ring from which the spiral arms appear to radiate rather than the normal bar or core, giving rise to its morphological classification of SAB(r)ab. Deep images also suggest that NGC 5566 has tidal plumes pulled out as part of the interaction. The spiral arms of NGC 5560 are also strongly distorted. NGC 5566 appears to be a LINER type AGN, perhaps not surprising as the interactions are likely to be feeding the black hole at its centre.

The group is about 85 million years or so away. The suggestion is that if the group is at this distance then NGC 5566 is about 150 million light-years across so much larger than our Milky Way and would be one of the largest galaxies in Virgo. There is a superb amateur image of this group.

Visually the group should contain challenges for all size telescopes. NGC 5566 should be visible in 20cm telescopes but to see NGC 5569 is probably going to require 45cm+. Luginbuhl and Skiff (L&S) suggests that 15cm should be enough to see NGC 5566 but I suspect this was form a high altitude site. I am guessing that since the Rosse team saw CGCG 047-019 then it should visible in 50cm+ so a nice challenge for large telescope observers. The triplet is compact enough that it should fit in a medium power (270x) field with a hyperwide field eyepiece. CGCG 047-019 (also known as PGC 51269) will also be in the same field. Of the NGC galaxies NGC 5690 is going to be the hardest to find as it is a face on low surface brightness object and probably only the core will be seen. NGC 5566 is part of the H400 II listing from the Astronomical League.

Owen Brazell - Galaxy Section Director