APOD: Magellanic Galaxy NGC 55 (2019 Jul 12)

[APOD Robot]

Magellanic Galaxy NGC 55

Explanation: Irregular galaxy NGC 55 is thought to be similar to the Large Magellanic Cloud (LMC). But while the LMC is about 180,000 light-years away and a well-known satellite of our own Milky Way Galaxy, NGC 55 is more like 6 million light-years distant, a member of the Sculptor Galaxy Group. Classified as an irregular galaxy, in deep exposures the LMC itself resembles a barred disk galaxy. Spanning about 50,000 light-years, NGC 55 is seen nearly edge-on though, presenting a flattened, narrow profile in contrast with our face-on view of the LMC. Just as large star forming regions create emission nebulae in the LMC, NGC 55 is also seen to be producing new stars. This highly detailed galaxy portrait highlights a bright core crossed with dust clouds, telltale pinkish star forming regions, and young blue star clusters in NGC 55.

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[Boomer12k]

Good image of the "Whale Galaxy"...

clicking on the image, and looking at the larger image and the lower left area...it looks to me to be some sort of merger going on...I know there are many forms of Irregulars...some are Diffuse, and devoid of mass... but this does not look like the case. In wide shots, there does not seem to be a nearby disrupting galaxy...maybe it ran into some NEW GAS... that had not formed into much of a galaxy at the time, and drawing it in made it explode in star formation...
If you look, there seems to be a bit of a "demarcation" between the two areas.

I think head on, there might be more of a "lopsided-spiral" view... but could be just me...

:---[===] *

[orin stepanek]

I think it looks like a mini spiral!

[BDanielMayfield]

I think head on, there might be more of a "lopsided-spiral" view... but could be just me...

:---[===] *

I think it looks like a mini spiral!

Yes. This is a most regular looking irregular galaxy. Indeed, in the Sculptor Galaxy Group link http://www.atlasoftheuniverse.com/galgrps/scl.html in the explanation it isn't even classified as an irregular. That reference lists it as "SBm", which makes it a barred spiral. I don't know what the "m" stands for here.

Bruce

[NGC3314]

Yes. This is a most regular looking irregular galaxy. Indeed, in the Sculptor Galaxy Group link http://www.atlasoftheuniverse.com/galgrps/scl.html in the explanation it isn't even classified as an irregular. That reference lists it as "SBm", which makes it a barred spiral. I don't know what the "m" stands for here.

The 'm' in such classifications stands for Magellanic, introduced in de Vaucouleurs' version of the Hubble galaxy classification to describe disk galaxies whose structure is one step less regular than even Sd which is a step less regular than the familiar Sc type. The type example is the Large Magellanic Cloud, which has a rotating disk and prominent bar, but maybe just barely any actual spiral pattern no matter how hard you squint. (This is still thought to be in step more organized than actual I-for-irregular systems). In NGC 55, the thought seems to be that it probably has a bar and, as said above, lopsided and messy spiral pattern, with the bar seen almost bed-on.

[BDanielMayfield]

Yes. This is a most regular looking irregular galaxy. Indeed, in the Sculptor Galaxy Group link http://www.atlasoftheuniverse.com/galgrps/scl.html in the explanation it isn't even classified as an irregular. That reference lists it as "SBm", which makes it a barred spiral. I don't know what the "m" stands for here.

The 'm' in such classifications stands for Magellanic, introduced in de Vaucouleurs' version of the Hubble galaxy classification to describe disk galaxies whose structure is one step less regular than even Sd which is a step less regular than the familiar Sc type. The type example is the Large Magellanic Cloud, which has a rotating disk and prominent bar, but maybe just barely any actual spiral pattern no matter how hard you squint. (This is still thought to be in step more organized than actual I-for-irregular systems). In NGC 55, the thought seems to be that it probably has a bar and, as said above, lopsided and messy spiral pattern, with the bar seen almost bed-on.

Thank you NGC3314. You provided a much better explanation of what the "m" means than what I was going to guess, which was "maybe".

[starsurfer]

Good image of the "Whale Galaxy"...

clicking on the image, and looking at the larger image and the lower left area...it looks to me to be some sort of merger going on...I know there are many forms of Irregulars...some are Diffuse, and devoid of mass... but this does not look like the case. In wide shots, there does not seem to be a nearby disrupting galaxy...maybe it ran into some NEW GAS... that had not formed into much of a galaxy at the time, and drawing it in made it explode in star formation...
If you look, there seems to be a bit of a "demarcation" between the two areas.

I think head on, there might be more of a "lopsided-spiral" view... but could be just me...

:---[===] *

The Whale Galaxy is NGC 4631. I don't think NGC 55 has a popular name?

[Ann]

Good image of the "Whale Galaxy"...

clicking on the image, and looking at the larger image and the lower left area...it looks to me to be some sort of merger going on...I know there are many forms of Irregulars...some are Diffuse, and devoid of mass... but this does not look like the case. In wide shots, there does not seem to be a nearby disrupting galaxy...maybe it ran into some NEW GAS... that had not formed into much of a galaxy at the time, and drawing it in made it explode in star formation...
If you look, there seems to be a bit of a "demarcation" between the two areas.

I think head on, there might be more of a "lopsided-spiral" view... but could be just me...

:---[===] *

The Whale Galaxy is NGC 4631. I don't think NGC 55 has a popular name?

Boomer, you're right:

Wikipedia wrote:

NGC 55, also occasionally referred to as The Whale Galaxy

Click to view full size image

NGC 55, the Whale Galaxy. Photo: Martin Pugh.

Click to view full size image

NGC 4631, the Whale Galaxy. Photo: Bieter Beer and Patrick Hochleitner.

But starsurfer, you are certainly right too. As I googled "The Whale Galaxy", I got pictures of and entries on NGC 4631 only. NGC 4631 really looks like a whale too, with that "fin" sticking out. The "fin" must be a spiral arm, of course. Clearly NGC 4631 is more whale-like than NGC 55, with its undulating "swimming" body.

NGC 4631 is very clearly tidally distorted by interactions with its small (but nevertheless hefty) satellite galaxy. Interestingly though, NGC 55 is also "distorted" (or lopsided). The disk of NGC 55 is a lot more elongated on one side of its yellowish bulge than on the other side of it. Perhaps NGC 55 is more like an extremely emaciated narwhal?

Click to view full size image

Mourning becomes Electra.
Spiral arms become the Large Magellanic Cloud.
Photo: Carlos Milovic.

Finally, since NGC 55 is said to be a Magellanic type galaxy (which I don't doubt that it is, don't get me wrong), I started hunting for images of the Large Magellanic Cloud, and I came across this one, which blew me away. I have no idea how the picture was made, so it may be so heavily and selectively processed that it has brought out features that may not actually be there. Even so, though, don't the spiral arms look good on our Large Magellanic neighbour?

Ann