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http://www.daviddarling.info/encyclopedia/M/Mirachs_Ghost.html wrote:

Mirach's Ghost (NGC 404) in visible light

Mirach's Ghost, GALEX ultraviolet image
Image credit: NASA/JPL-Caltech/DSS

<<[Mirach's Ghost is a] dwarf lenticular galaxy of type S0 in the constellation Andromeda that is seen almost face-on. Although of high surface-brightness, it is difficult to observe, because of the glare of Mirach (M0 red giant Beta Andromedae), just 7 arc-minutes away. NGC 404 is typical of spheroidal galaxies in that it has few luminous, young stars but a high proportion of red giants and asymptotic giant branch (AGB) stars. Red giants dominate in the disk, while the bulge of the galaxy is populated by both red giants and AGB stars.

NGC 404 was discovered by William Herschel in 1784. It lies just beyond the edge of the Local Group and appears not to be gravitationally bound to it. Although it has been listed as a loose member of the LGG 011, it is probably physically unassociated with it and may well be the nearest iS0lated S0 galaxy, its nearest neighboring galaxy being at least 1.1 Mpc (3.6 million light-years) away.

For many years the distance to NGC 404 was very uncertain, estimates ranging from 1.5 megaparsecs (Baars & Wendker 1976) to 10 Mpc (Wiklind & Henkel 1990). Only recently has the distance become reasonably well known using two independent methods. In 2001 Tonry et al. used the surface brightness fluctuation method to arrive at a distance of 3.3 Mpc (10.8 million light-years). This was confirmed the following year by Karachentsev et al. who used the tip of the red giant branch to obtain a distance of 3.15 ± 0.32 Mpc.

NGC 404 is one of the nearest examples of an early-type galaxy to the Milky Way, and shows an unusual amount of activity for such a system. It is surprising rich in interstellar atomic and molecular gas, has a prominent, semicircular dust lane that encircles the nucleus, and has a number of bright ultraviolet point sources. It was first classified as a LINER by Schmidt et al. in 1990. Observations (Barbon et al., 1982) using photographic surface photometry revealed the presence of a bulge, lens, and disk components, characteristic of a lenticular galaxy and ruling out the possibility, suggested by some astronomers, that it might be a dwarf elliptical.

In 2008, observations in the ultraviolet by NASA's Galaxy Evolution Explorer revealed a ring of young stars surrounding the well-known, very old stellar population. Previous imaging with the Very Large Array radio telescope had discovered a gaseous ring of hydrogen that matches this ultraviolet ring. The authors of the Very Large Array study attributed the gas ring to a violent collision between NGC 404 and a small neighboring galaxy 900 million years ago. The ultraviolet observations show that, when the hydrogen from the collision settled into the plane of the lenticular galaxy, new stars began to form. The findings indicate that the evolution of lenticular galaxies might not yet be complete. They may, in fact, continue to form stars in a slow, piecemeal fashion as they suck the raw, gaseous material for stars from small, neighboring galaxies.>>

Ann wrote:Let's see if I can post Mirach's Ghost where you were unsuccessful, Art.

Click to view full size image

We'll see if this works. On the left is a visual light image, and on the right is an ultraviolet image of Mirach and Mirach's Ghost taken by GALEX. I would think that the yellow star seen in the ultraviolet image to the lower left of the galaxy, in a seven o'clock position, would be Mirach in ultraviolet light.

Ann

ChrisKotsiopoulos wrote:

Ann wrote:Let's see if I can post Mirach's Ghost where you were unsuccessful, Art.

Click to view full size image

We'll see if this works. On the left is a visual light image, and on the right is an ultraviolet image of Mirach and Mirach's Ghost taken by GALEX. I would think that the yellow star seen in the ultraviolet image to the lower left of the galaxy, in a seven o'clock position, would be Mirach in ultraviolet light.

Ann

Well done Anthony!

rstevenson wrote:I don't think your interpretation of the UV image is correct, Ann. If it was, then the Ghost galaxy would be vastly larger seen in UV than in visible light, and that doesn't seem to be what they're saying in the description.

I don't think your interpretation of the UV image is correct, Ann. If it was, then the Ghost galaxy would be vastly larger seen in UV than in visible light, and that doesn't seem to be what they're saying in the description.

The first images of the Ghost of Mirach taken by the Galaxy Evolution Explorer hinted at a surrounding ultraviolet-bright extended structure. Subsequent, longer exposure observations indeed show that the lenticular galaxy is surrounded by a clumpy, never-before-seen ring of stars.