Celestial hemisphere:  Northern  ·  Constellation: Hydra (Hya)  ·  Contains:  NGC 2718  ·  PGC 1296501  ·  PGC 25203  ·  PGC 25205
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UGC 4703 Stellar Bridge & TDG, plus NGC 2718, Gary Imm
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UGC 4703 Stellar Bridge & TDG, plus NGC 2718

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UGC 4703 Stellar Bridge & TDG, plus NGC 2718, Gary Imm
Powered byPixInsight

UGC 4703 Stellar Bridge & TDG, plus NGC 2718

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Description

This object captures two fascinating objects in the constellation of Hydra at a declination of +6 degrees.

UGC 4703 is the pair of faint interacting dwarf galaxies in the upper right part of the image, located 170 million light years away. UGC 4703 (PGC 25205) is the 17 magnitude dwarf galaxy near the center of the image, while UGC 4703B (PGC 25203) is the fainter 19 magnitude dwarf galaxy to the upper right. The view of UGC 4703B is compromised a bit by a distant galaxy immediately to its lower right.

This pair is well described in the 2017 paper, “UGC 4703 Interacting Pair Near to an Isolated Spiral Galaxy NGC 2718: A Milky Way Magellanic Cloud Analogue”, by Paudel and Sengupta. The 2 galaxies are connected by a magnificent 80,000 light year long star stream bridge. On the left side of this bridge is a very faint 20.4 magnitude clump of stars identified as a TDG, or Tidal Dwarf Galaxy. A TDG is defined as a stellar system which has its origin in expelled debris of interacting galaxies.

Although the star stream was the focus of the image, I was pleasantly surprised by NGC 2718, on the lower left side of the image. NGC 2718 is about the same distance away as UGC 4703 so they could be interacting. NGC 2718 spans 2 arc-minutes in our apparent view, which corresponds to an actual diameter of 120,000 light years.

There are so many interesting things to see in this galaxy. The core has a bluish color which I thought was an artifact, but the SDSS image looks similar. The outer disk looks disturbed, with 2 main arms but also an arm segment on the left side. The most interesting feature is the straight bright white bar which extends from the right side of the core down to the lower left mid-region of the galaxy. I have never seen such an asymmetric straight feature before, not centered on the core. Near the center of this bar, a distinct narrow dark dust lane cuts across it at 90 degrees.

The paper concludes that this main galaxy + 2 dwarf galaxy system almost 200 million light years away is a good analog to our Milky Way system (Milky Way, LMC & SMC), being similar in geometry, star formation rate, gas mass and stellar mass.

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