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M 86
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M 86

February 19, 2005
Lenticular (S0) Galaxy M86 (NGC 4406), type S0, in Virgo

Right Ascension: 12 : 26.2 (h:m)
Declination: +12 : 57 (deg:m)
Distance: 60000 (kly)
Visual Brightness: 8.9 (mag)
Apparent Dimension: 7.5x5.5 (arc min)

Discovered 1781 by Charles Messier.

M86 has been discovered and cataloged by Charles Messier on March 18, 1781 when he also cataloged 7 more nebulous objects in the same region of the sky, all member galaxies of the Virgo Cluster, and in addition, globular cluster M92.

This bright giant galaxy is either an elliptical of type E3 or a lenticular galaxy of type S0_1(3); modern classifications apparently tend more to the lenticular classification, NED gives both classes. It has a conspicuous system of faint globular clusters, suggestions of which can be just seen in the DSSM image of this galaxy. However, this system of globulars is far less populated than that of its giant neighbor to the SE, M87. To the lower left is a very small and faint dwarf elliptical companion. Several condensations may be found around this galaxy in our image, especially to the lower part, and the DSSM photo (here to the upper edge), they may be globular clusters belonging to this galaxy.

M86 lies well in the heart of the Virgo Cluster of galaxies and forms a most conspicuous group with another giant, M84. Below M86 in our image is NGC 4402, a dim (11.5 mag) edge-on spiral. This group may be viewed in one field even at medium power, so that it is often photographed and we have more images including M84 and M86. Deep images of this group have revealed that these galaxies are actually much larger than indicated in conventional images, as the one in this page. In addition, we have images of the whole central part of the Virgo Cluster: M87 together with Markarian's chain around M84 and M86.

M86 is the galaxy which has the fastest approaching velocity, and thus the highest blue shift, of all Messier galaxies (and thus all Messier objects): It is approaching us at 419 km/sec ! (Sky Catalogur 2000.0; NED has a slightly lower value of 281 km/sec which makes it second to M90.) Holmberg (1964) has therefore speculated that it should be a close foreground galaxy and not a Virgo cluster member. This speculation has been referred to, and occasionally been adopted, by several sources, including George R. Kepple's and Glen W. Sanner's Observer's Guide. However, the present authors join the view of most modern sources, including the Sky Catalogue 2000.0, R. Brent Tully's Nearby Galaxies Catalog, Becvar's earlier Atlas Coeli, and (implicitely) the Webb Society's Deep Sky Observer Handbook (which has it in the Virgo Cluster description), and thinks it is just this high approach velocity which indicates that M86 is most probably a true cluster member, because of the following reason: In this case, the high velocity value would indicate that M86 is moving at a peculiar velocity of more than 1500 km/sec, which points by chance in a direction toward us. But this is not totally uncommon in huge clusters of galaxies as the Virgo cluster, because due to its enormous mass, this huge agglomeration of mass has a strong gravitational field. This strong gravitational field could easily accelerate a galaxy to the high velocity observed for M86; it would be much more difficult to find an explanation for such a high velocity for a field galaxy !

The Virgo cluster membership of M86 is also suggested by its more or less obvious interaction with the intergalactic gaseous matter in the Virgo cluster, which was reported from X-ray observations, discovered by Forman et.al. (1979); for a recent review see e.g. Rangarajan et.al. (1995). Moreover, M86 does not hold the record: Another Virgo cluster member, IC 3258, approaches us at 517 km/sec. Our Galaxies in the Virgo Cluster page lists more fastly approaching (and receding) Virgo Cluster members.

The X-ray gas tail of M86 is dramatically apparent in recent Chandra X-ray Observatory images of this galaxy.

Additional evidence for M86's Virgo Cluster membership may be derived from deep images of this galaxy which show slight disturbations of its faint outskirts, probably caused by gravitational interaction with its neighbors.

On deep images like this one, the outskirts of M84 and M86 seem to overlap; the angular distance between their centers of about 16.5 arc min corresponds to a projected distance of only roughly 300,000 light years. This, however, is probably a perspectivic effect, as otherwise their outlayers would be even much more distorted; there is probably some radial distance, or distance difference from us, between these two galaxies; it is not known which one is a bit closer to, and which a bit farther away from us.

On M86's fast motion through the intergalactic medium of the Virgo Cluster (the "Intra-Cluster Matter", ICM), the galaxy's interstellar matter collides at high velocity with this material, and is probably "ram-pressure stripped" from the galaxy (Rangarajan et.al. 1995). On this occasion, the matter is heated. Dust within this matter, previously held within colder gas clouds, is probably destroyed when the matter heats during the collision. Analysis of the ram pressure indicates that, in addition to its peculiar radial velocity with respect to the Virgo Cluster, M86 may have a tangential velocity component of about 500 km/sec in southward direction.

M86, together with M84, can be found rather easily, by pointing your telescope almost exactly half-way between Denebola (Beta Leonis) and Vindemiatrix (Epsilon Virginis). Both galaxies will show up in the same low (or medium) power eyepiece, and can serve as starting point for Observing the Virgo Cluster. Alternatively, you can find M84 and M86 from the "Big T" asterism including 6 Comae Berenices which is near M98, M99, and M100 at 1 deg south and 1.5 deg East of this asterism's "Southern Tip" star. Or both these galaxies are easily found from M87 which is about 1 degree southeast.


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