rwlott wrote: ↑Fri May 01, 2020 1:51 pm
I'm curious about the faintly visible bluish galaxy at the right edge of the image, just right of the blue foreground star. Does this galaxy have a name/designation? Are there any larger images of it?
A quick search turned up only one other picture of the blue galaxy you asked for, in an image by Fabian Neyer. My guess, for what it's worth, is that this tiny galaxy probably does have a designation, but I have no idea what it would be. The galaxy is very faint. How faint? Perhaps 16th magnitude? 17th?
Also note that while the little galaxy is blue in both images, its color is not as saturated or "deep" in Fabian Neyer's picture as it is in Joonhwa Lee's. We don't expect galaxies to be deeply blue in color. But this galaxy is definitely blue and therefore full of hot massive stars. Note that we can just barely make out a central bulge that appears bluish, but not as blue as the disk. There is an appreciable amount of old red stars in the bulge, but there are young stars there, too.
The blue disk "sticking out" from the bulge appears to be brightest at the ends. That is an interesting luminosity distribution.
Here is what I think might possibly be going on. Take a look at the image at right. It is a crop from an APOD by Ken Crawford (2014 June 25), and it shows a few galaxies in the Hercules Cluster of galaxies. At upper right, you can see the remarkable interacting trio
NGC 6050/Arp 272 in an image by Hubble Legacy Archive/ Martin Pugh.
Below NGC 6050, you can see a blue ring galaxy. Actually, the ring is somewhat faint, but the bar inside the ring is bright. Can you see that the bar is bright blue at the ends?
At upper left, you can see a yellowish galaxy that is slightly similarly shaped, except it doesn't have a ring. It has a bright center, an elongated shape, and it is brighter at the ends of its disk (or bar?). So maybe the tiny blue galaxy in the APOD is actually a bright blue bar with a central yellowish bulge in the middle?
The picture at left shows 11.3 magnitude galaxy NGC 4217 in a picture by Fabian Neyer. The small blue galaxy you asked about is located in the lower right corner. The picture at right shows 11.4 magnitude galaxy NGC 4424, and small 15.2 magnitude galaxy LEDA 213994. The small galaxy also has an IC designation, though: IC 3366.
So as you can see, the two larger galaxies in the two pictures are almost exactly equally bright, and there are two small edge-on background galaxies located close or relatively close to them in the sky. In my opinion, LEDA 213994/IC 3366 looks a lot brighter than the small blue galaxy you were asking for. So the blue galaxy is definitely not a 15th magnitude object. I don't think it's a 16th magnitude object either. So 17th magnitude? Maybe?
As you can see, IC 3366/LEDA 213994 appears to have a relatively bright surface brightness. It is also located where it might be moderately easy to spot, just at the visible edge of a relatively bright galaxy. By contrast, the small blue galaxy appears to have a lower surface brightness, and it is also smaller in size and located farther out in the "wilderness". It may have a designation, perhaps in the LEDA catalog, but I'm not inclined to look for it.
Let me say a few words about the foreground stars next to the small blue background galaxy in both Joonhwa Lee's and Fabian Neyer's images. The sharply blue-looking star really is quite blue as stars go. It is a star of spectral class B8, and it is much bluer than Sirius and Vega, and also bluer than Regulus or Alkaid at the end of the handle of the Big Dipper. It is bluer than any of the stars in the Pleiades. At a color index of -0.125, it is not as blue as the blue stars of Orion, but yes, it is blue. Eighth magnitude stars in the field of galaxies are rarely as blue as this.
As for the rather deeply orange star next to it, SAO 44089, it is a star of spectral class K5, and its B-V index is about +1.8. That is not as red as Betelgeuse, but yes, it is pretty red. So yes, these stars are colorful.
Ann
A View Toward M106
M106 and NGC 4217 very beautiful in this scene!
