The Magnificent Leo Triplet of Galaxies: M65, M66 and NGC 3628
Object data:
M65: RA 11h 19', Dec +13 05', size 9.8’ x 2.9’, mag 9.3
M66: RA 11h 20', Dec +12 59', size 9.1’ x 4.0’, mag 8.9
NGC 3628: RA 11h 20', Dec +13 35', size 14.8’ x 3.3’, mag 9.5
Most deep sky observers, at one time or another, have slewed their scopes to the famous Leo Triplet of Galaxies. Situated at an easy to locate spot at the “hind legs” of the constellation Leo, these galaxies are a popular star party target and one of the first amateur astronomer targets (at least the two more obvious members). But these popularity and “beginner deep sky observer stuff” tags have caused a great neglect to these galaxies by serious, advanced, “faint fuzzy” hunters. Yet, as we shall soon see, the Leo Triplet offers tons of observing challenges and pleasures for amateurs of all levels.
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The Leo Triplet as photographed from my backyard!
Before dealing with observing the Leo Triplet, let’s first discuss the galaxies from an “astrophysics” point of view. The Leo Triplet is made up from Messier 65, Messier 66, and NGC 3628. The triplet is included in Arp’s catalog of peculiar galaxies as Arp 317 (amongst the category “galaxy groups”), while M66 is individually listed as Arp 16 (category “Spirals with detached segments”). All three galaxies are interacting spirals, located approximately 30 million light years from the Earth. As a result their shapes are somewhat distorted. Both M65 and M66 are type SB spirals. M65, which is approximately 60,000 light years across, appears relatively normal, with tightly wound arms, which though on close examination of high resolution photographs, appear warped. M66, at 50,000 l.y. across, is definitely warped, with several knots and one spiral arm that is significantly “heavier” than the others, somewhat reminiscent of a crab’s pincer. NGC 3628 is physically the largest of the three at almost 80,000 l.y. across. It is an unbarred spiral seen edge-on, with a broad dust lane splitting it in half. The edges of the galaxy though appear distorted and fan out. Even the dust lane appears to be skewed, further indicating interactions with its neighbors. In addition, a 260,000+ light year long tidal tail has been detected on very deep images. This tidal tail, along with the “peanut-shaped” central bulge of the galaxy, further reinforce the idea of galactic interaction between the members of the group.
Let’s move on now to what can be visually seen in this group. All three galaxies can fit into the wide field of view of most telescopes. M65 has a magnitude of 9.3, while M66 is the brightest of the three at 8.9. NGC 3628 is a bit fainter at 9.5, but, being larger both physically and visually, it suffers from a low surface brightness, thus it is the hardest to see. M65 and M66 appear on the southern part of the field of view, at right angles to NGC 3628 which (if seen!) dominates the northern part of the field.
Under clear, moonless skies M65 and M66 are detectable even in 10x50 hand held binoculars, and are immediately obvious in any telescope. NGC 3628, due to its low surface brightness, is much harder to detect. I was able to detect and hold steady with direct vision all three galaxies using my 22x60 tripod mounted binoculars. M65 appeared as a tiny spindle of light, while M66 was a tiny pear shaped glow. NGC 3628 was barely there as a thin ghostly glow. Very faint, but steadily held with direct vision. I was though unable to detect 3628 using hand held 10x50 or 9x63 binos under the same sky.
With NicosK’s 90mm f10.1 achromatic refractor I could again see straight away both M65 and M66, using a Scientific Explorer 30mm eyepiece. M65 was a quite distinct, long spindle of faint light with a brighter center, while M66 was more of an oval light with a very bright center. It took some effort to detect NGC 3628, but once located it could be held with direct vision – most of the time! Certainly NGC 3628 was easier in the 60mm binoculars than in the 90mm refractor. Moving to an 100mm apo refractor at 63X, all three galaxies appeared brighter, with NGC 3628 being more distinct than before, the dark lane being suspected at times.
My 150mm refractor offered significantly improved views. All three galaxies could be seen with direct vision, and could fit in the same field of view given by the 13mm Ethos at 69X. At higher magnifications, M65 could be seen as a long lens-shaped galaxy with a broad, considerably brighter center. M66 was slightly smaller but appeared brighter, with a very bright condensed core and some anisotropy, with some vivid brightness at the southern edge. NGC 3628 was significantly bigger in the eyepiece, but still much fainter than the other two galaxies. The most important difference though was in the visibility of the dust lane – despite the faintness of the galaxy, a broad dust lane was visible, even with direct vision.
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Needless to say, my 18” Obsession gave far more spectacular views.
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M65 was very long, Iits length to width ratio approaching 6:1. It appeared significantly longer in the 18” at all powers compared to the smaller scopes. This may be attributed (I guess!) to the fact that the outer regions of the spiral arms became faintly visible. There was a bright, small (but not quite stellar) nucleus, which at high powers seemed to be surrounded by a dark “eyeliner” shape. I am not sure if I could see dark lanes or if it was just a contrast effect from the bright nucleus and the outer, tightly wound arms. This effect was visible even at the relatively low power of 66X, but was very definite at 159X and even at 275X. Photos do indicate a thin dust lane surrounding the nucleus.
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With the big dob the appearance of M66 was also greatly improved. The galaxy assumed an oval shape with diffused edges. The central area was dominated by a very bright bar-like core running north – south, with a very bright nucleus. Again, the central area appeared to be surrounded by a dark lane. A distinct brightening appeared at the southwesterernmost edge of the galaxy – the big, crab-pincer like spiral arm visible in photos. At medium and high powers this arm assumed the shape of a club, or baseball bat. The dark lane surrounding the core appeared most distinct to the south, next to the “baseball bat”. Unlike M65, I can’t see a corresponding distinct dark lane in photos, so I presume that in the case of M66 the dark lane is a contrast effect.
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Even with the huge light gathering ability of eighteen inches, NGC 3628 remains rather faint. Not excessively so, but certainly much fainter than the other two galaxies. What it lacks in brightness though, the galaxy makes up in detail. First of all it is huge, with a length of almost 15'. The western and eastern edges of the galaxy do appear to fan out exactly like seen in photos. But by far the most spectacular feature of this galaxy is the relatively thick dark lane. The dark lane appears very distinct, with a bit of scalloping at its edges, and is warped. Also, it does not run along the entire length of the galaxy: It seems to begin at the southern edge of the galaxy about 4’ from the eastern end, runs close to the southern edge, and exits again on the southern edge of the galaxy about 4’ before reaching the galaxy’s western end. Although the real core of NGC 3628 is hidden behind the dusky clouds of the dust lane, there is an increase in brightness north of the dust lane, for the entire length of the dust lane. This brightening was was readily detectable, and seems to be in disagreement with Barbara Wilson’s observation of “very evenly illuminated along entire length” as listed in Kanipe and Webbs’s “The Arp Atlas of Peculiar Galaxies”. By the way, 5 quasars ranging from the 19th to 22nd magnitude can be found around NGC 3628. These appear to be beyond the reach of my 18” but they could be game for those with really large scopes.
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So, the magnificent Leo Triplet of galaxies provides many challenges: What are the smallest binoculars to detect all three galaxies? What is the minimum aperture for spotting NGC 3628, and how much aperture is needed for its dust lane, or for details on and around the lane? What are the optimal magnifications for teasing out the subtle details of M65 or the club-like thick spiral arm of M66?
So, next time you are under dark and steady skies,
“GIVE IT A GO AND LET US KNOW”!
GOOD LUCK AND GREAT VIEWING!
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