APOD: NGC 1365: Majestic Island Universe (2018 Dec 28)

[APOD Robot]

NGC 1365: Majestic Island Universe

Explanation: Barred spiral galaxy NGC 1365 is truly a majestic island universe some 200,000 light-years across. Located a mere 60 million light-years away toward the chemical constellation Fornax, NGC 1365 is a dominant member of the well-studied Fornax galaxy cluster. This impressively sharp color image shows intense star forming regions at the ends of the bar and along the spiral arms, and details of dust lanes cutting across the galaxy's bright core. At the core lies a supermassive black hole. Astronomers think NGC 1365's prominent bar plays a crucial role in the galaxy's evolution, drawing gas and dust into a star-forming maelstrom and ultimately feeding material into the central black hole.

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[BDanielMayfield]

Looking to see this galaxy in the context of its neighborhood I note from looking at http://heritage.stsci.edu/2005/09/supplemental.html (the "Fornax galaxy cluster" link) that NGC 1365 is the only large spiral in its group. It is quite removed from the center of the cluster's mass which is full of photographically dull ellipticals.

Yeah, NGC1365 is a classy galaxy all right, but our Local Group sports three gorgeous spirals! We Local Groupers got it all over Fornax. And, as far as the constellational setting goes, Fornax, forget 'boud it! What an empty hole in the sky.

[Boomer12k]

Don't go to the middle...it's a TRAP!!!!

Great image...

:---[===] *

[Ann]

Looking to see this galaxy in the context of its neighborhood I note from looking at http://heritage.stsci.edu/2005/09/supplemental.html (the "Fornax galaxy cluster" link) that NGC 1365 is the only large spiral in its group. It is quite removed from the center of the cluster's mass which is full of photographically dull ellipticals.

Indeed! There has been speculation that NGC 1365 does not in fact belong to the Fornax galaxy cluster.

Yeah, NGC1365 is a classy galaxy all right, but our Local Group sports three gorgeous spirals! We Local Groupers got it all over Fornax. And, as far as the constellational setting goes, Fornax, forget 'boud it! What an empty hole in the sky.

Yes, the part of our galaxy that we call Fornax is pretty boring, isn't it? Although Fornax does contain two pretty nice blue stars with nice negative B-V indexes, Delta and Nu. All right, don't thank me so much for telling you this... I'm overwhelmed...

Of course, the fact that Fornax is so boring in terms of bright stars (and dust) is exactly the reason why it is so good at showing off its galaxies.

On a slightly more serious note, this is a very pleasant APOD. NGC 1365 is a very photogenic galaxy, and it shows off its colors beautifully through HαLRGB filters!

Ann

[heehaw]

The ESPOD has a galaxy too!

[BDanielMayfield]

Looking to see this galaxy in the context of its neighborhood I note from looking at http://heritage.stsci.edu/2005/09/supplemental.html (the "Fornax galaxy cluster" link) that NGC 1365 is the only large spiral in its group. It is quite removed from the center of the cluster's mass which is full of photographically dull ellipticals.

Indeed! There has been speculation that NGC 1365 does not in fact belong to the Fornax galaxy cluster.

They (the NGC1365ers) probably insist that they aren't part of the Fornax rabble, even if they are.

[sillyworm 2]

What are the factors(if known) that decide whether a galaxy has a single arm or multiple spiral arms?

[Ann]

What are the factors(if known) that decide whether a galaxy has a single arm or multiple spiral arms?

Click to view full size image

Extremely few galaxies have just a single arm. One example of such a one-armed galaxy is NGC 4725. (But if you look carefully at the picture of NGC 4725, you can see what looks like a second (short) arm sprouting from about 6 o'clock and bending upwards and to the right.)

Click to view full size image

NGC 1097. Photo:
Spitzer Space Telescope.

Click to view full size image

NGC 1672. Photo: GALEX.

Not many galaxies are truly two-armed, either. NGC 1097 at left is an example of a galaxy that is fairly two-armed.

Most spiral galaxies have more than two arms. NGC 1672 at right is an example of a "mostly two-armed" galaxy that is sprouting several secondary arms.

My amateur impression is that the disks of starforming galaxies rather easily break up into multiple arms. I also think that galaxies with strong bars more easily develop just two arms instead of multiple arm structures, compared with unbarred galaxies or galaxies with weak bars. Moreover, I think that large massive galaxies more easily develop an elegant spiral system than smaller, more lightweight galaxies.

Click to view full size image

M81 and M82.

Also, I think that "just the right degree of disturbance" may enhance the formation of just two spiral arms. I think M81 (at left) owes its elegant two-armed shape to interactions with M82 at right, and NGC 3077 off the frame at upper left, and small companion galaxy Holmberg IX "above" M81.

Click to view full size image

NGC 2857. Photo: SDSS.

I also want to show you one of the most elegant and perfect two-armed spiral galaxy that I know of, NGC 2857. In the SDSS picture at right, you can see that there are some other galaxies in the field, and it is just possible that NGC 2857 is interacting a little bit with one or more of them.

Click to view full size image

NGC 4625 (top) and NGC 4618.
Photo: GALEX.

I should add that UV images taken by the GALEX telescope are particularly good at revealing outer arm structures, since many (but not all) spirals form optically faint outer arms that are comparatively bright in ultraviolet light. In the picture at left, NGC 4625 at top is revealed to sport a large and intricate set of previously undiscovered ultraviolet-bright arms.


(By the way, this GALEX picture of NGC 1365 shows NGC 1365 to be mostly two-armed, and generally lacking in outer arms.)

Ann