Celestial hemisphere:  Southern  ·  Constellation: Eridanus (Eri)  ·  Contains:  NGC 1721  ·  NGC 1723  ·  NGC 1725  ·  NGC 1728
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NGC 1721 Galaxy Group, Gary Imm
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NGC 1721 Galaxy Group

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NGC 1721 Galaxy Group, Gary Imm
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NGC 1721 Galaxy Group

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Description

This object is a galaxy group located 200 million light years away in the constellation of Eridanus at a declination of -11 degrees. All of the 5 large galaxies in this image are about the same distance away.

NGC 1721 is the large face-on spiral ring galaxy in the center of the image. I am not sure why it is the namesake of the group - NGC 1723 on the left edge is brighter and just as large. NGC 1721 is a magnitude 12.9 galaxy which spans 3 arc-minutes, corresponding to a diameter of 180,000 light years. It has a bright barred core and a solid inner disk, the brightest part of which has an interesting subtle S-shape. The ring on the outside of the disk is likely due to gravitation disturbance with nearby galaxies.

Below NGC 1721 is the bright lenticular galaxy NGC 1725. I originally thought that NGC 1725 was an elliptical galaxy, but there is some structure in the disk upon close examination.

Rounding out the central trio of galaxies is NGC 1728, a near edge-on galaxy with a fascinating structure. I see two strong dust rings encircling the bright core. Most interestingly, the forward and back edges of the disk appear to be in shadow, if that were possible. It looks like there is a bright stripe running through the galaxy from upper left to lower right. I thought this was an artifact at first, but other images also show this unique structure. I have no idea what could cause this.

NGC 1723 is the most interesting galaxy of the five, in my opinion. The galaxy has so many interesting features - a bright strong barred core with ansae at each end with star clusters, a strong inner ring, two classic long arms, and a highly disturbed section towards the bottom with a wide star stream moving away from the central trio. The inner ring is my favorite part - I love how the shading of the ring changes, starting as bright white at each ansae, and then progressively getting dimmer as you move clockwise around the ring (until reaching the next ansae).

Closing out the five large galaxies here is the edge-on galaxy at lower right, MCG-02-13-031.

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