Celestial hemisphere:  Northern  ·  Constellation: Draco (Dra)  ·  Contains:  NGC 5963  ·  NGC 5965  ·  NGC 5969  ·  NGC 5971
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A Quartet of Galaxies in Draco: Warped, Wheezy, Wonted, and Woolly, Howard Trottier
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A Quartet of Galaxies in Draco: Warped, Wheezy, Wonted, and Woolly

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A Quartet of Galaxies in Draco: Warped, Wheezy, Wonted, and Woolly, Howard Trottier
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A Quartet of Galaxies in Draco: Warped, Wheezy, Wonted, and Woolly

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Description

This field of view in Draco contains a quartet of galaxies with contrasting morphologies that I like to characterize using the alliteration (starting near the top of the field and winding counter-clockwise around the frame): Warped, Wheezy, Wonted, and Woolly.

The "warped" galaxy at the top is the nearly edge-on spiral NGC 5965, the tips of which appear to be bent away from the dominant plane of the galaxy. The "wheezy" spiral near the bottom-left corner is NGC 5971, which has a jet emerging from the core that fans into an extended star stream to the right, as if forcibly exhaled, while the galaxy also seems to have been shaped by tidal forces, with a distorted disk, and an extended cloud on the left (more on a possible source of these disruptions below). Over to the right is the compact elliptical galaxy NGC 5969, which can arguably be described as "wonted", in the sense that galaxies are "wont" to be elliptical, the most common galaxy type. Last in this sequence is the flocculent or "woolly" spiral NGC 5963 (flocculent spirals, which represent about 30% of all spiral galaxies, lack well-defined arms, while about 10% of spirals have a so-called "grand-design", which generally consists of two symmetric and well-defined arms, and 60% have multiple arms).

Although the two most prominent galaxies in the image might appear to be associated with one other, given their relatively small angular separation, and similar apparent angular diameters, they are in fact far apart and unrelated: the nearly edge-on spiral is about 150 million-light years away, with a diameter of about 200,000 light-years, while the nearly face-on flocculent spiral is much closer, at a distance of about 40 million light-years, and it has a diameter of only about 100,000 light years.

The origin of the jet-like activity and tidal distortion of the "wheezy" galaxy NGC 5971 appears to be an open question, with little if any discussion to be found in the literature. The elliptical galaxy NGC 5969 is unrelated, despite the fact that it appears to be roughly in line with the jet from NGC 5971, as it has almost four times the redshift of the other galaxy, which indicates that it is much further away.  I noticed however that the redshift of NGC 5971 is almost identical to the redshift of the "warped" spiral NGC 5965:  the recessional speed of NGC 5971 is 3365 ± 2 km/sec, while that of NGC 5965 is 3377 ± 2 km/sec, which are about 1% of the speed of light, but with a relative radial motion some 25 times smaller than that of the Andromeda Galaxy relative to the Milky Way. This seems unlikely to be a coincidence, and suggests that they are at nearly the same distance (unfortunately there has been no "direct" estimate of the distance to NGC 5971). If true, then the two galaxies could have caused tidal disturbances in one another, although it is an open question whether the apparent warp in NGC 5965 is an artifact of projection, or an actual physical distortion.

This image is the result of just under 11 hours of integration in luminance, and 8 hours in RGB colour, and was taken over the course of six nights in May and June. The plate scale is about 0.62"/pixel, and the field-of-view is about 29'x22'.

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A Quartet of Galaxies in Draco: Warped, Wheezy, Wonted, and Woolly, Howard Trottier