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Old 18-07-2011, 10:28 PM
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madbadgalaxyman (Robert)
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NGC 3628 : a boxy & X shaped Bulge, plus a peculiar dust lane

Following on from the discussion between myself and Les in the Observation Reports post "AGCS 805 Observed"...... regarding the various types of bulges that can be found in spiral and S0 galaxies, I present a few images of NGC 3628 in the Leo Triplet, emphasizing various interesting features of this strange galaxy.

Firstly, a negative image showing the strange "x" shape projections above the plane of this galaxy:

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Now I present a Near-infrared image from the 2MASS survey, which removes much of the complex and confusing extinction that is caused by the equatorial dust lane:

Click image for larger version

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Now that the effect of much of the obscuring dust has been removed, you will note that the "X"-shaped bulge is actually symmetric, with all four arms of the X being present.
Another important feature revealed here is that the main body of this galaxy, seen here minus much of the dust, is not particularly distorted, despite the unusual bending or bifurcation of the dust lane that is seen in visual/optical imagery.

Thirdly, I present an image at high contrast, showing how very boxy ("rectangular") the bulge of this galaxy can look when seen at certain scalings:

Click image for larger version

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The subtle structure of the bulge of this galaxy is relatively easy to discern in these images, because of its nearness.
But this bulge shape is common enough in some Galaxy Cluster and Galaxy Group environments!

However, the case for NGC 3628 being a peculiar galaxy is proven when it is imaged to faint isophotes and displayed at very high contrast:

Click image for larger version

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As we all know, spiral and S0 galaxies, because they are thin and disk-like in three-dimensional space, show themselves to the eye and camera as ovals.
However, this galaxy is very noticeably rectilinear ("rectangular") at faint isophotes!!

cheers,
mad galaxy man

P.S.
At the website http://burro.cwru.edu/JavaLab/GalCrashWeb
, Chris Mihos and colleagues present the results of simulations showing that the apparent Warping & Tilting & Thickening of the disk component of NGC 3628 is plausibly caused by the accretion (cannibalization) of a companion galaxy which had about 10 percent of the mass of NGC 3628 .

Last edited by madbadgalaxyman; 18-07-2011 at 11:57 PM. Reason: additional info to be added
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