Saturday, May 8, 2021

The NGC 70 galaxy group

The NGC 70 galaxy group (also known as Arp 113, or VV 166) is a cluster of galaxies, located at a distance of around 300 million light years in the constellation of Andromeda. 

It was discovered in 1784 by William Herschel as a single object, but a century later, John Emil Dreyer was able to distinguish individual galaxies in the region.

The cluster consists of a diverse population of galaxies. Observations have revealed a striking structure that nearly forms an equilateral triangle. At its top is NGC 70, a spiral galaxy, the lenticular galaxy NGC 71 is to its lower left, while the elliptical galaxy NGC 68 is on its lower right.

NGC 70 experiences intense star formation in its arms, thus due to its young stellar population appears bluer in optical images. NGC 68 on the other hand is an elliptical galaxy which means it is dominated by old stars, thus it appears monochromatic. Finally, NGC 71 since it is a lenticular galaxy, it displays colors from both galactic types we just saw.

Due to their proximity of the three galaxies, there is evidence of interaction between them. The spiral arms of NGC 70, appear distorted between its two neighbors, suggesting that the three galaxies experience tidal forces.

Finally, below the galactic triangle, a spiral barred galaxy known as NGC 72 is located. The galaxy appears to be isolated, thus there is no evidence of interaction. The elliptical galaxy PGC 1208 (also known as NGC 72A) is left of NGC 72, while on the right of the latter is the lenticular galaxy NGC 69. The two galaxies right of the triangle are known as NGC 67A (up) and NGC 67 (down). The first is an elliptical, while the second is a lenticular.

Image: Composite optical image of the NGC 70 Galaxy Group taken with the Gemini North Telescope in Hawaii. The image was created using broadband filters that are centred at 475 nm (B-band, blue), 630 nm (V-band, green), and 780 nm (I-band red).

Image Credit: International Gemini Observatory/AURA 

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