Starship Asterisk*

IFN and the NGC 7771 Group

Explanation: Galaxies of the NGC 7771 Group are featured in this intriguing skyscape. Some 200 million light-years distant toward the constellation Pegasus, NGC 7771 is the large, edge-on spiral near center, about 75,000 light-years across, with two smaller galaxies below it. Large spiral NGC 7769 is seen face-on to the right. Galaxies of the NGC 7771 group are interacting, making repeated close passages that will ultimately result in galaxy-galaxy mergers on a cosmic timescale. The interactions can be traced by distortions in the shape of the galaxies themselves and faint streams of stars created by their mutual gravitational tides. But a clear view of this galaxy group is difficult to come by as the deep image also reveals extensive clouds of foreground dust sweeping across the field of view. The dim, dusty galactic cirrus clouds are known as Integrated Flux Nebulae. The faint IFN reflect starlight from our own Milky Way Galaxy and lie only a few hundred light-years above the galactic plane.

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There is a lot to see in this APOD!


The stellar streams from the interacting pair of NGC 7771/NGC 7770 appear to mix with the IFN of the Milky Way, so that it's hard to say where the NGC 7771 star streams end and the Milky Way Integrated Flux Nebula begins. Note that the star streams of the other galaxies and the IFN of the Milky Way are the same color, meaning that they are made of the same kind of old red stars.

NGC 7769 has an interesting appearance. The inner spiral arms are blue and pink from young stars and star formation, but the long broad outer arms are beige from old stars. Since the inner and the outer spiral arms are connected, the arms of NGC 7769 make two full turns around the core of the galaxy, which is a lot indeed. Compared to NGC 7771, NGC 7769 seems relatively undisturbed.

When it comes to color, one galaxy stands out, namely LEDA 214993. This is a blue galaxy, dominated by stars hotter and considerably younger than the Sun. But LEDA 214993 is also very small and faint, only 17th magnitude!

Note the somewhat disturbed appearance of the IFN. It may have been shaped by outbursts from inside our galaxy.

Just a few days ago, AVAO (jac) made a post about astrophotographer Mark Hanson, and jac included a link to Mark Hanson's galactic star stream images. Two of Mark Hanson's star stream images show the NGC 7771 group:


Note the faint IFN to the left of NGC 7771 in Mark Hanson's images.

For comparison, I found another color picture of the NGC 7771 group, by Lorenzo Siciliano, Francesco Corrao and Aldo Grassi.


Here the IFN is barely visible. But to me at least, the (white-looking) star formation in NGC 7771 and NGC 7770 stand out better in the Lorenzo Siciliano image than in the APOD. We don't see any pink nebulas in NGC 7769 in the Lorenzo Siciliano image, however. Note the small "electric blue" star to the right of NGC 7769. This star looks white in the APOD.

Ann

Ann wrote: ↑Sat Aug 31, 2024 6:33 am it's hard to say where the NGC 7771 star streams end and the Milky Way Integrated Flux Nebula begins
Ann

I wonder if the red shift from 200 millions ly away can help