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| Object |
Type |
Size |
Mag |
RA |
Dec |
| M 84 |
Galaxy |
6.5'x5.6' |
9.2 |
12h 25m 30.7s |
+12° 50' 18" |
| M 86 |
Galaxy |
8.9'x5.8' |
8.9 |
12h 26m 38.6s |
+12° 53' 52" |
| NGC 4435 |
Galaxy |
3.0'x2.2' |
10.8 |
12h 28m 07.6s |
+13° 01' 52" |
| NGC 4438 |
Galaxy |
8.5'x3.0' |
10 |
12h 28m 12.7s |
+12° 57' 36" |
| NGC 4458 |
Galaxy |
1.6'x1.5' |
11.8 |
12h 29m 24.8s |
+13° 11' 37" |
| NGC 4461 |
Galaxy |
3.4'x1.4' |
11.1 |
12h 29m 30.0s |
+13° 08' 09" |
| NGC 4473 |
Galaxy |
4.5'x2.5' |
10.2 |
12h 30m 15.7s |
+13° 22' 52" |
| NGC 4477 |
Galaxy |
3.7'x3.3' |
10.4 |
12h 30m 29.0s |
+13° 35' 18" |
You may note that the images
are a little larger this month. Usually I size to 600 pixels in
deference to those amateurs who use displays running at 800x600, but
given the nature of these targets, for this month I've decided to try
running the article sized for a screen running at 1024x768, with photos
at 800 pixels wide. If you don't like this format, please drop me
a line and let me know.
Ah Spring, when a not-so-young man's mind (at least in
my case) turns to thoughts of galaxies. For many seasoned Deep
Sky observers, there's no better time of the year. As the snow
melts, and we begin to emerge from our igloos, our bleary eyes drift
towards the night sky. Our telescopes now wander through Leo,
Virgo and Coma Berenices gathering ancient photons from esoteric
denizens of this celestial zoo.
If you're like me, you spend a great deal of time in that agglomeration
of galaxies labeled the Coma-Virgo cluster. The SEDS page for the
Virgo cluster calls it the "the largest proven structure in our
intergalactic neighborhood, and the most remote cosmic objects with a
physical connection to our own small group of galaxies, the Local
Group, including our Milky Way galaxy."
The Virgo cluster is the heart of our own local supercluster
(confusingly enough labeled the Virgo Super-cluster). By
gravity, these giants are bound to us, or if you prefer we are bound
to them. Here then, lies our eventual destiny.
For an observer with a moderate to large telescope, targets
abound. And even a small scope can keep one busy for hours
here. I revisited the area this spring with a TeleVue 85,
and quickly got lost. Good charts are a must when you're headed
into this area. There are just so many galaxies.
Sitting astride the Virgo / Coma Berenices border, deep in the heart of
the Coma-Virgo cluster of galaxies, we find one of springs finest
showpieces; a bright galaxy grouping known as Markarian's
Chain. In December 1961, the Astronomical Journal published
a paper by Beniamin Egishevich Markarian (1913 - 1985) entitled -
"Physical Chain of Galaxies in the Virgo Cluster and Its Dynamic
Instability". In this three page paper, Markarian laid out a
probabilistic analysis of the hypothesis that the bright galaxy chain
starting in Virgo with the M84/M86 pairing, then curving up into Coma
Berenices and concluding with NGC4477 was in fact not a simple chance
alignment of galaxies, but an actual physical associated
chain. In essence, he used statistics to argue that
"...the small probability of the chain being formed by chance speaks
strongly in favor of the hypothesis that the chain is a physical
system."
There's still debate about the physical association of the chain,
but one thing nearly everyone can agree on is that it's a superb
grouping for visual observers, and one of the clear highlights of the
spring sky.
While Markarian laid out 8 galaxies for the interaction
hypothesis (see the above image), there's some disagreement amongst
amateurs as
to exactly what galaxies should included in this grouping for our own
purposes. The most common additions propose adding NGC4459 and
NGC4474 to end at M88, or even continuing on to M91 and NGC4571.
This makes sort of a galactic asterism (galasterism?) for deep sky
observers.
One thing is for sure, there is no shortage of deep sky objects in the
area. Markarian's paper comments that the Shapely-Ames
catalog puts 88 galaxies brighter than mag 13 in a region with a seven
degree radius centered around this area, and there are some where
around 1500 to 2000
galaxies in the Virgo cluster as a whole. Jared Wilson notes he "
...was able to find 38 different galaxies
ranging in magnitude from 8.6 (M87) to approximately 16.4 (IC 3445)" in
his spectacular image shown below.
Image
Courtesy Jared Wilson
And visual observer Sebastian Szalai notes the following when observing
with his 10" dobsonian - "
Spotted 16
galaxies in Markarian's Chain at 192x - they are: M86, M84,
NGC 4388, 4402, 4387, 4413, 4425, 4435, 4438, 4461, 4458, 4473, 4477,
4479, 4459 and 4474."
Personally, when I refer to the chain I pay homage to
the individual who "discovered it" and typically stay with the
classical
grouping of 8 galaxies, and thus we'll define the limits of the subject
for this article.
I've viewed the Chain (or parts of it anyway) in everything from 80mm
apos up to 20" dobs, the
components are all pretty high magnitude, and have decent surface
brightness. (A neat trick is to use a widefield scope and see if
you can get the entire chain in the field at the same time and then see
how many you can actually identify.) I've not attempted it with
binoculars, but I suspect
that if you were so inclined, you might have some good luck - at least
with M84 and M86. I'd suggest large aperture and high
magnifications - at a minimum 10x50s - along with some good charts to
help pick these guys out. If you've managed part of the chain
with binoculars, I'd really love to hear about it.
To find these, you're going to need a few pretty decent charts -
Finder chart 1 shows stars down to mag 6.5 and is intended to "get you
in the general area".
Finder Chart 2 lists stars to mag 9.
Finder 3 goes down to mag 13. Also note, we're only showing the
galaxies of interest in these charts.
Here's a DSS image of the area to aid in identification. Note the
chain begins on the right middle with M84 and M86, so that's where we'll
start.
Messier
84 / Messier 86
Although these two are an optical pair, they really aren't the twins
you might suspect.
M84 is classed (via NED - Nasa/IPAC Extragalactic Database) as an
E1 elliptical and while viewing DSS images certainly looks that
way. M86 is an S0 - the first lenticular that follows the
pure ellipticals. 84 shines with the luminosity of 55.8 billion suns, while M86 greets us with the
luminosity of some 61.1 billion suns. M84 is an active emitter of radio radiation
and was recently confirmed (by hubble) to have a massive black hole at
its center.
Above we see the Wide Field Planetary Camera 2 image of M84. The blue
region marks where the Space Telescope Imaging Spectrograph was
used. From the red and blue shift visible in the STIS image, the
orbital velocity of the gas around center was determined and from that they obtained the
mass of the core. STIS data determined that 300 million solar
masses are concentrated within a distance of 26 light years from the
center. The most likely candidate for something this massive is a black
hole.
Visually, it's all too easy to classify galaxies like these as mere
whiff's of cotton in the night - more similar than anything else, but
there are some differences for the visual observer. Take some
time and give them a good inspection; use higher powers and see if you
can see any change in their structure. Can you spot any
differences? In particular look for M84 fading smoothly
into the background and for an extended halo surrounding M86. M86
looks larger to me, but in a small scope, 84's core seems a bit
brighter.
Both M84 and M86 were "discovered" and catalogued by Messier on the
night of March 18th, 1781. According to SEDS, Messier also
cataloged six other objects in that area on this evening. Having
recently been lost there (again) with a Tele Vue 85 I'm somewhat
surprised that he only cataloged 8 total that evening.
Image
Courtesy Gary Beal
Gary Beal submitted the above image of the southern end - Try using it
as a training ground to see what galaxies you can pick out.
Copeland's
Eyes (NGC 4438 / 4435)
Buried within Markarian's Chain (specifically 4438 type Sa, and
4435 type S0) we find Arp 120, otherwise known as Copeland's
Eyes. In a 1955 piece in Sky and Telescope, Leland Copeland
called these two galaxies The Eyes as representative of their
appearance in the eyepiece.
Arp classified these under "Elliptical close to and perturbing
spirals". The question arises - which is the perturber, and which
is the perturbed? Arp suggested 4435 was responsible for
affecting 4438, but in the Carnegie Atlas of Galaxies, Sandage and
Bedke suggest that the current state of 4438 has nothing to do with
4435 but rather another merger of which whose galaxies are no longer
individually visible.
See page 301 in The Arp Atlas of Peculiar Galaxies - a Chronicle and
Observer's Guide (Kanipe and Webb) for more details. In there,
you'll find notes from Barbara Wilson - a CN forum member - describing
their visual appearance in her 20" f4 newtonian.
NGC
4461 / 4458, NGC 4473 and NGC 4477
Markarian's (Classical) Chain now begins its wind down with the the
NGC 4461 / 4458 pair. NGC 4461 is classed as an SB0-a and
at visual magnitude 11.1 is both the larger and brighter of this pair,
while 4458 is listed at visual mag 11.8, and classed as an
E. Following this we have NGC 4473, a 10.2 mag
(visual) E galaxy and finally SB0 NGC 4477.
In smaller scopes like my 4" apo,
I find 4461 is just a bright slash - almost stellar at very low powers,
and 4458 can be overlooked entirely. 4473 and 4477 fare better
but honestly, while these are pretty bright galaxies they are
significantly
overshadowed by the Messier showpieces in the area. In my mind
they make
for an interesting sight mainly because of their association with the
chain.
Sketch Contributed by
Vedran Vrhovac
And with that, that's it for this one. Once again, thanks to the
readers who submitted observations, sketches and photos, there were far
more excellent submissions this month than I could use. Your
contributions greatly enrich these articles.
As always, I'm gratified if folks find my meanderings useful.
Till next time -
-
Tom T.
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Resources / References / Just Plain Cool Stuff
