M84&86: Galaxy Field of Dreams
Introduction Some Useful Facts ... ... And Intriguing Thoughts At the Eyepiece Parting Thoughts Farewell Fellow Galactophiles!
Introduction
The seeds of galaxy-quest lie within each of us... Regardless of whether we use large scopes, or small, we can span the Limitless Ocean of Space to visit distant "Island Universes"!
In this exciting episode of "Galaxy Quest", we take a step on our endless journey and spend some "quality time" with "twin" galaxies M84 and M86 in Virgo.
Galaxy pair M84 & M86, like more distant M85, are part of the Coma-Virgo Galaxy Cluster. The pair - plus M85 - lie near the center of the Local Supercluster which includes our own Local Group of galaxies. At heart of this huge collection is the supergiant elliptical galaxy M87.
Galaxies M84, 86, & M87 were all discovered in the year 1781 by comet-hunter Charles Messier. Galaxy M85, of similar size and luminosity, was first logged that same year by Messier's associate Pierre Méchain. 1781 would prove to be the pinnacle of Messier's productivity, for later in the season he suffered a mishap and spent the next year recovering. Not too long after this, the Torch of Deep Sky Discovery was passed to William Herschel. Charles Messier then went on to add several comets to his list of discoveries before passing in the Spring of 1817 at the age of 87.
top of pageSome Useful Facts ...
Like M85, the M84/86 pair is best observed in early Spring just after skydark. Though the pair may be located through a 2 inch or larger scope, most satisfying views are seen through 200 millimeter (and larger) instruments under dark skies.
M84 Virgo, Type: Galaxy, Magnitude: 9.3, Apparent Size: 5x4' RA: 12 25.1, Dec:12 53, Optimal Scope Size: 200mm.
M86 Virgo, Type: Galaxy, Magnitude: 9.2, Apparent Size: 7x6' RA: 12 26.2, Dec:12 57, Optimal Scope Size: 200mm.
... And Intriguing Thoughts
While contemplating this pair, two ideas of some intrigue surface. First, after turning up a few of the brightest galaxies in the region, Charles Messier went off to explore elsewhere. This left Messier's associate (Pierre Méchain) the opportunity to harvest the twelve remaining bright galaxies (M88 - M100) found there. It would appear that Charles Messier wasn't into mopping up!
Second, and more uniquely, is the fact that the M84/86 locale bears a resemblence to the Hubble Deep Space Galaxy Field - a region of intense galactic concentrations on the very edge of the HST's photographic reach. As such, this region is the amateur's "Not-So-Deep Space Galaxy Field". By lavishing time and attention thereon, one can make of it "The Galaxy Field of Dreams"...
At the Eyepiece
We begin our tour by "getting small". Although this pair of 200mm-optimal elliptical galaxies may be turned up in a 50mm scope, little more than a certain "vague fuzziness and ill-defined central brightening" is possible. At 40x, a good 75mm achromatic rich field refractor begins to distinguish each galaxy's core within a faint core region. No sense of galactic orientation is possible. (However, the nice dark background sky such scopes ubder modest magnifications and conditions makes both galaxies obvious in the field of view!)
So far - no "Field of Dreams"....
A 114mm newtonian reflector, reveals these galactic mates with little effort. During average seeing, the M84/86 pair expands on an 80mm refractor's ease of distinction. The two galaxies appear a "matched set" of readily discerned "twin ellipticals". As such, both display well distributed core regions, but little else to give each its unique due.
On moderately dark nights (5.5 ULM), averted vision begins to hint at the fainter riches this area holds. But, a larger collection of photons is needed to begin serious prospecting in the region!
At 150mm, the western member of the pair (M84) is seen slightly brighter and visibly smaller. With an average surface brightness (ASB) of magnitude 12.2, M84 is brighter than more distant Virgo cluster member M85 - while at ASB 12.9, M86 is slightly dimmer. In terms of apparent size, M84 shows maybe 3 arc minutes of face-on presentation. Like M85 further afield, M84 displays a star-like nucleus surrounded by a bright core, enshrouded with wispy nebulosity. Under eye movement, M84 appears to swell in every direction. Since there is no particular direction of flare, the sense of "face-on" presentation is readily reinforced.
In the same field as M84 (east and slightly north) lies M86. This galaxy's nucleus is broader, and less intensely brilliant, than that of M84. On eye movement through 150mms, its core position shifts slightly north. (This as M86's luminosity diffuses south.) In apparent size, M86 is about 1/3rd larger than M84. A bit more than half its full extension can be seen through a six inch scope.
Despite less dramatic structure, M86 holds visual attention just as well as its brighter, more compact, confrere.
Using 318mms in aperture, we see the galaxies literally "leap" out of the eyepiece. This even at the most modest magnifications! (Not surprising, huh? The 12.5 is well beyond the 200mms needed to get an "optimal view" of this face-on pair.) Under direct vision, one's attention is immediately riveted on these intense galaxies. Strangely though, additional prominent structure fails to be seen. As such, M84 gains very little besides a brighter appearance over the six inch instrument.
Increased magnification reveals only slightly more than what can be viewed with a good six inch scope on a dark night. The major difference is that all detail is immediately present - no tricks of the eye required. M84's central concentration is notably more diffuse and its' fade to the outer frontier is more dignified.
At 318mm, galaxy M86 shows somewhat better form. Evidence of flattening appears along the longer edges. There is a sense that the galaxy is being "squeezed together" by the combined influence of the billions of stars that make it up! Finally, there is even a "hint of resolution" along the edges....
Beginning at 6 inches - and more so at 12.5, one of the most fascinating features of this area becomes apparent. While studying the bright galactic forms of the M84/86 with direct vision, aversion begins to welcome many other mysterious strangers into view. As noted, M84 and 86 dwell in a galaxy-rich region of space. Within a single 40 arc-minute field of view, and with a little effort, a six inch scope can reveal three other companions!
Forming an easy (almost equilateral) triangle with the two Messier's (and located about 20 arc-minutes south) lies NGC4388. At magnitude 11.0 and 5X1 arc minute apparent size, this edge-on spiral has an ASB of 12.4. As such, you'd think it would show as much structure as the brightest of the Messiers! But, this is not the case. All that is possible is to get a sense of NGC4388's spatial orientation (east-west) and size (maybe 3/4 X 3 arc-minutes). Sharp-eyed observers using six inch scopes may also be able to detect a dim, star-like 13 plus magnitude core - but increased sensitivity due to eye movement may be essential.
At magnitude 12.0, 2x1 arc-minute sized NGC4387 is also a 12.4 magnitude average surface brightness galaxy. This NGC galaxy is conveniently located in the midst of a triangle formed of the two Messiers and NGC4388. Despite a relatively bright ASB, NGC4387 requires 120X for definitive detection - especially on marginal nights of seeing. Eye movement may also give this faint galaxy a hint of a stellar nucleus as well.
While no real structure on the NGC4388 is possible at 6 inches of aperture, a 12.5 reveals a touch of definition under averted vision. As such, the galaxy takes on the classic form of an edge-on spiral. And we here at Galaxy Quest especially like our galaxies edge-on!
Experience tells us that locating one arc-minute sized galaxies often requires higher magnifications. At lower overall magnitudes, their small cores are often indistingushable from faint stars. Increased magnification darkens the sky and spreads available light out. This combination improves contrast and reveals their non-stellar natures. The eye also makes distinctions based apparent "size". As such, size, contrast, and luminosity are very important factors in eyepiece detection. For these reasons, higher magnifications are often needed when attempting to track down dim galaxies approaching 1 arc-minute in extent and magnitudes near a particular apertures limit for sky conditions.
As a result, NGC4387 is a tough customer in both scopes. Under 318mm inspection, a very small face-on spiralesque structure with round "stellar" nucleas is possible. The galaxy's light disperses more or less evenly to its' frontier. Despite another magnitude and a half of reach and use of highest available magnifications, details can not be easily pulled out of this one, (And reflect on the wonder it can be located at all at in telescopes with one quarter the light gathering capacity!)
Meanwhile, moderate magnifications (138x) shows that NGC4388 possesses an evenly illumined core region. A certain "stretched appearance" is possible at the margins. Finally, the western frontier can be seen notably thinner and more diffuse.
About 10 arc-minutes north of M86 is an even dimmer swatch of nebulosity - NGC4402. Bearing an ASB of magnitude 12.9, galaxy 4402 appears "distinctly" ill-defined. Like NGC4387, 4402 demands moderate magnifications (120X) through a six inch instrument for confident detection.
Gathering four times the light does have its advantages! Bearing an apparent size of 4x1 arc-minutes, there is enough of NGC4402 to make its' presence well known. The galaxy displays edge-on structure. This improves its' contrast immensely. Large apertures at high power (300x) reveals a noticeable dust lane. The central structure forms a curved "bar" of light. Luminosity appears evenly distributed end to end, while the dust lane cleanly clips the classic central bulge of the core.
We've now gone as 'deep" as we can. East of M86 are two brighter NGC galaxies - 4435 and 4438. 4435 is roundish (3X2 arc-minutes) and bears a visual magnitude of 10.8. 4438 is larger (9 X 3) and cumulatively brighter (10.1). At 12.4 and 13.4 ASB respectively, neither are particularly difficult. And their larger apparent sizes support lower magnifications nicely.
Through a six inch, galaxy 4435 - like its nearby sibling - is easily picked out at low power (50X). Scrutiny at 120X shows about 2 round arc-minutes of wispy luminosity containing a bright star-like core. A slight amount of flaring northeast to southwest is possible as the eye moves across the field.
While NGC4435 consists of simple star-like core/wispy round body structure, Galaxy 4438 adds a dim, 1 arc-minute sized core region plus beginnings of edge-on extensions northeast and southwest. These details are barely perceptible through a six inch and only under eye movement. In general, NGC4438 looks pretty much like 4435 - except a tad brighter.
Even at 318mm, ellipitical galaxies tend to be rather uninteresting creatures, but the beauty of the NGC4435 and NGC4438 are their proximity to each other. The 4435 shows true elliptical structure, evenly illuminated - with a sense of fading toward the edges... But the 4438 is quite a different story! This elliptical is much more elongated. A highly conspicuous wisp of galactic material can be seen stretching back toward the brighter, nearby galaxy pair M84/86: A faint arm of luminosity reaching toward the greater light.
Parting Thoughts
Studying a galaxy complex can be both frustrating and highly rewarding. Frustrating in that highly developed skills of mind, hand, and eye are needed to make confident identification of specific galaxies possible. Rewarding, because we denizens of the Blue Planet tend to find our greatest joy and satisfaction in pushing the envelop and overcoming our limitations.
It is our hope that the information provided in this article offers you the inspiration and guidance needed to reach for the stars!
Farewell Fellow Galactophiles!
From the "Not-So-Deep Space Galaxy Field" and "The Field of Dreams", we wish you...
Clear Skies and Happy Hunting!
(c) 2002 Tamela Jean Watt/Plotner & Jeff Barbour
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