APOD: NGC 7331 and Beyond (2023 Sep 14)

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APOD: NGC 7331 and Beyond (2023 Sep 14)

Post by APOD Robot » Thu Sep 14, 2023 4:05 am

Image NGC 7331 and Beyond

Explanation: Big, beautiful spiral galaxy NGC 7331 is often touted as an analog to our own Milky Way. About 50 million light-years distant in the northern constellation Pegasus, NGC 7331 was recognized early on as a spiral nebula and is actually one of the brighter galaxies not included in Charles Messier's famous 18th century catalog. Since the galaxy's disk is inclined to our line-of-sight, long telescopic exposures often result in images that evokes a strong sense of depth. The effect is further enhanced in this sharp image by galaxies that lie beyond the gorgeous island universe. The most prominent background galaxies are about one tenth the apparent size of NGC 7331 and so lie roughly ten times farther away. Their close alignment on the sky with NGC 7331 occurs just by chance. Lingering above the plane of the Milky Way, this striking visual grouping of galaxies is known to some as the Deer Lick Group.

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Re: APOD: NGC 7331 and Beyond (2023 Sep 14)

Post by Ann » Thu Sep 14, 2023 6:14 am


It's a nice image. I like it.

The APOD is "red-forward". You'd think that as a lover of blue things, I'd hate a picture that "leans toward the red", but in this case the red color just shows us where there is red hydrogen alpha emission and thus star formation. There is definitely a value in knowing that.

People process their images in different ways, and bring out colors in various ways. I'd say that there are some rights and wrongs here, but there is a wide variety of acceptable choices. The choices made for today's APOD are definitely all acceptable.

But there are other ways of showing us NGC 7331 and the Deer Lick Group, too:


Adam Block is one of my all-time favorite astrophotographers, and I love all the subtle colors in his picture. You can see that he brings out a lot more blue in his picture than Ian Gorenstein does. Then again, Starship Asterisk*'s resident astronomer, Chris Peterson, would tell you that galaxies are all gray. Well, to each his or her own.

It is really very interesting that NGC 7331 is seen right in front of the galaxy group known as the Deer Lick Group, which is at least 8 times farther away from us than NGC 7331 (some 300-350 million light-years away versus some 40 million light-years away for NGC 7331). I find it interesting that the galaxies of the Deer Lick Group appear to have been "fraying away" on each other and stealing and dispersing one another's gas supplies until they have become a group of "mostly elliptical galaxies". Well, not quite elliptical, because NGC 7337 is definitely a barred spiral galaxy, although one with hardly any star formation:

NGC 7337 SDSS.png
Barred "Deer Lick" spiral galaxy NGC 7337. Credit: SDSS.


As interesting as the Deer Lick Group galaxies are, there is another, even more interesting galaxy group in the "vicinity" of NGC 7331 (although again much further away), namely Stephan's Quintet. I just found a pretty lovely picture showing NGC 7331, the Deer Lick Group and Stephan's Quintet together:


Linda, I love that picture of yours! I hope I was allowed to copy it. You have chosen to emphasize the gas streams in and around the galaxies (including the IFN, the Integrated Flux Nebula, which is high cirrus clouds in the Milky Way), which gives your image a wonderful sense of fluidity and motion.

I think your image is mirror-reversed, so that Stephan's Quintet should be at the lower left of NGC 7331 instead of at the lower right of it (at least if north is up and east to the left, which is the conventional way of showing deep-sky astronomical objects). But that is a very minor quibble.

Ann
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Last edited by Ann on Thu Sep 14, 2023 5:06 pm, edited 1 time in total.
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Re: APOD: NGC 7331 and Beyond (2023 Sep 14)

Post by Christian G. » Thu Sep 14, 2023 1:36 pm

There are many ways to try to fathom just how huge galaxies are, and when they are inclined in a way we can appreciate their depth as in this APOD, I tell myself: this is not a snapshot image of the whole galaxy 50 millions years ago, only the light from the front part may be that old, but the light from the rear is 100 000 years older. Such that if humans had evolved at the same time and rate on two different planets both formed around the same epoch over there, one in the rear and one in the front of the galaxy, in the front we would see humans capable of space travel, while the ones in the rear would still be cavemen!

Wonderful picture…

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Re: APOD: NGC 7331 and Beyond (2023 Sep 14)

Post by AVAO » Thu Sep 14, 2023 3:16 pm

Ann wrote: Thu Sep 14, 2023 6:14 am
It's a nice image. I like it.

The APOD is "red-forward". You'd think that as a lover of blue things, I'd hate a picture that "leans toward the red", but in this case the red color just shows us where there is red hydrogen alpha emission and thus star formation. There is definitely a value in knowing that.

Ann
ThanX Ann for your analysis, which surprises me a bit. The processing of the image is technically stringent:
Filter: Astronomik Type 2c Blue 36 mm · Astronomik Type 2c Green 36 mm · Astronomik Type 2c Luminance 36 mm · Astronomik Type 2c Red 36 mm · Baader H-alpha 6.5nm (CMOS-Optimized) 36 mm

To be honest, visually I don't really like the result aesthetically appealing. The inner normal yellow regions are colored the same red as the outer red star formation regions. However, when I compare this with Adam Block's image, which has significantly different colors, I cannot understand the red coloring in the galaxy arms. But ok. If the technical processing is correct, the cause of the red streaks would be an exciting research question, as they do not correlate with Adam Block's star formation regions. Nevertheless, the pictures from Ian Gorin on his Astrobin page are great. Personally, I would have simply chosen another...

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Re: APOD: NGC 7331 and Beyond (2023 Sep 14)

Post by pferkul » Thu Sep 14, 2023 3:37 pm

Ann wrote: Thu Sep 14, 2023 6:14 am
It is really very interesting that NGC 731 is seen right in front of the galaxy group known as the Deer Lick Group, which is at least 8 times farther away from us than NGC 7331 (some 300-350 million light-years away versus some 40 million light-years away for NGC 7331). I find it interesting that the galaxies of the Deer Lick Group appear to have been "fraying away" on each other and stealing and dispersing one another's gas supplies until they have become a group of "mostly elliptical galaxies".
I know nothing about intergalactic mass transfer, but what evidence is there that the galaxies have been "fraying away" on each other? They are all still very far from each other, ~40 MLY, so I would have thought the fraying effect would be relatively small.

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Re: APOD: NGC 7331 and Beyond (2023 Sep 14)

Post by VictorBorun » Thu Sep 14, 2023 5:30 pm

is it me or the core is quite spherical?
NGC 7331 and Beyond.JPG
NGC 7331 and Beyond-.JPG
...
Click to view full size image 1 or image 2
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Re: APOD: NGC 7331 and Beyond (2023 Sep 14)

Post by johnnydeep » Thu Sep 14, 2023 5:45 pm

Three questions: why is the background group of galaxies called the Deer Lick Group? My googling was mostly in vain, though it did find a group of astrophotographers that call themselves that.

And in the Astrobin page for this image, it states these attributes:
RA center: 22h37m04s.1
DEC center: +34°24′54″
Pixel scale: 0.569 arcsec/pixel
Orientation: 177.512 degrees
Field radius: 0.250 degrees
What is "orientation"? The orientation of the ...image?... with respect to ... what?

Also, I take it that the "field radius" has something to do with the FOV of the image, but this image isn't square, so to what does the "radius" refer?
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Re: APOD: NGC 7331 and Beyond (2023 Sep 14)

Post by Ann » Thu Sep 14, 2023 6:01 pm

pferkul wrote: Thu Sep 14, 2023 3:37 pm
Ann wrote: Thu Sep 14, 2023 6:14 am
It is really very interesting that NGC 731 is seen right in front of the galaxy group known as the Deer Lick Group, which is at least 8 times farther away from us than NGC 7331 (some 300-350 million light-years away versus some 40 million light-years away for NGC 7331). I find it interesting that the galaxies of the Deer Lick Group appear to have been "fraying away" on each other and stealing and dispersing one another's gas supplies until they have become a group of "mostly elliptical galaxies".
I know nothing about intergalactic mass transfer, but what evidence is there that the galaxies have been "fraying away" on each other? They are all still very far from each other, ~40 MLY, so I would have thought the fraying effect would be relatively small.
I just meant that galaxies that exist in close proximity to one another for a long time tend to lose their gas and their starforming ability. And the galaxies of the Deer Lick Group are pretty close to one another.


Take a look at these galaxies in a small part - note! A small part! - of the Coma Cluster of galaxies:


You can see that most galaxies here are yellow, but one is strikingly blue. The blue galaxy is IC 4040. However, by far most galaxies in the Coma Cluster are yellow. Take a look at this more wide field image of the Coma Cluster by Kurious George:


A spiral galaxy is showing off prominently at upper center and slightly to the right. This is NGC 4921. But NGC 4921 is no ordinary spiral galaxy:


The harsh environment of the Coma Cluster is causing NGC 4921 to be losing its gas. Soon it will not be able to form any more stars. This is what typically happens to galaxies in crowded conditions.

I'd say that the Deer Lick Group is sufficiently crowded to have caused the individual member galaxies to lose most of their gas, turning them into yellow galaxies with little or no star formation.

Ann
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Re: APOD: NGC 7331 and Beyond (2023 Sep 14)

Post by Chris Peterson » Thu Sep 14, 2023 6:29 pm

johnnydeep wrote: Thu Sep 14, 2023 5:45 pm Three questions: why is the background group of galaxies called the Deer Lick Group? My googling was mostly in vain, though it did find a group of astrophotographers that call themselves that.

And in the Astrobin page for this image, it states these attributes:
RA center: 22h37m04s.1
DEC center: +34°24′54″
Pixel scale: 0.569 arcsec/pixel
Orientation: 177.512 degrees
Field radius: 0.250 degrees
What is "orientation"? The orientation of the ...image?... with respect to ... what?

Also, I take it that the "field radius" has something to do with the FOV of the image, but this image isn't square, so to what does the "radius" refer?
The orientation of the image with respect to north (declination 90°). The conventional orientation would be 0°, which would be north up east left.

I believe the "Radius" value is reporting the size of the circle around the center coordinates used to search for stars used for the plate solve.
Chris

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Re: APOD: NGC 7331 and Beyond (2023 Sep 14)

Post by johnnydeep » Thu Sep 14, 2023 8:10 pm

Chris Peterson wrote: Thu Sep 14, 2023 6:29 pm
johnnydeep wrote: Thu Sep 14, 2023 5:45 pm Three questions: why is the background group of galaxies called the Deer Lick Group? My googling was mostly in vain, though it did find a group of astrophotographers that call themselves that.

And in the Astrobin page for this image, it states these attributes:
RA center: 22h37m04s.1
DEC center: +34°24′54″
Pixel scale: 0.569 arcsec/pixel
Orientation: 177.512 degrees
Field radius: 0.250 degrees
What is "orientation"? The orientation of the ...image?... with respect to ... what?

Also, I take it that the "field radius" has something to do with the FOV of the image, but this image isn't square, so to what does the "radius" refer?
The orientation of the image with respect to north (declination 90°). The conventional orientation would be 0°, which would be north up east left.

I believe the "Radius" value is reporting the size of the circle around the center coordinates used to search for stars used for the plate solve.
Thanks!
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Re: APOD: NGC 7331 and Beyond (2023 Sep 14)

Post by orin stepanek » Thu Sep 14, 2023 8:39 pm

LRGBHa23_n7331r_800c.jpg
Another beautiful galaxy!
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Re: APOD: NGC 7331 and Beyond (2023 Sep 14)

Post by Cousin Ricky » Thu Sep 14, 2023 8:45 pm

I wonder if anyone has dubbed this the Leet Galaxy.

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Re: APOD: NGC 7331 and Beyond (2023 Sep 14)

Post by Chris Peterson » Thu Sep 14, 2023 8:47 pm

pferkul wrote: Thu Sep 14, 2023 3:37 pm
Ann wrote: Thu Sep 14, 2023 6:14 am
It is really very interesting that NGC 731 is seen right in front of the galaxy group known as the Deer Lick Group, which is at least 8 times farther away from us than NGC 7331 (some 300-350 million light-years away versus some 40 million light-years away for NGC 7331). I find it interesting that the galaxies of the Deer Lick Group appear to have been "fraying away" on each other and stealing and dispersing one another's gas supplies until they have become a group of "mostly elliptical galaxies".
I know nothing about intergalactic mass transfer, but what evidence is there that the galaxies have been "fraying away" on each other? They are all still very far from each other, ~40 MLY, so I would have thought the fraying effect would be relatively small.
They are currently that far apart. But they are in complex orbits around each other, which means there have likely been quite a few near misses and glancing blows over the age of the Universe.
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Re: APOD: NGC 7331 and Beyond (2023 Sep 14)

Post by johnnydeep » Thu Sep 14, 2023 9:06 pm

Cousin Ricky wrote: Thu Sep 14, 2023 8:45 pm I wonder if anyone has dubbed this the Leet Galaxy.
I don't get it. :?
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Re: APOD: NGC 7331 and Beyond (2023 Sep 14)

Post by Chris Peterson » Thu Sep 14, 2023 9:30 pm

johnnydeep wrote: Thu Sep 14, 2023 9:06 pm
Cousin Ricky wrote: Thu Sep 14, 2023 8:45 pm I wonder if anyone has dubbed this the Leet Galaxy.
I don't get it. :?
Actually, it would be Teel.
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Re: APOD: NGC 7331 and Beyond (2023 Sep 14)

Post by johnnydeep » Fri Sep 15, 2023 12:20 pm

Chris Peterson wrote: Thu Sep 14, 2023 9:30 pm
johnnydeep wrote: Thu Sep 14, 2023 9:06 pm
Cousin Ricky wrote: Thu Sep 14, 2023 8:45 pm I wonder if anyone has dubbed this the Leet Galaxy.
I don't get it. :?
Actually, it would be Teel.
Yeah, not getting that one either.
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Re: APOD: NGC 7331 and Beyond (2023 Sep 14)

Post by Chris Peterson » Fri Sep 15, 2023 1:18 pm

johnnydeep wrote: Fri Sep 15, 2023 12:20 pm
Chris Peterson wrote: Thu Sep 14, 2023 9:30 pm
johnnydeep wrote: Thu Sep 14, 2023 9:06 pm

I don't get it. :?
Actually, it would be Teel.
Yeah, not getting that one either.
"7331" is how you write "TEEL" in Leet.
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Re: APOD: NGC 7331 and Beyond (2023 Sep 14)

Post by johnnydeep » Fri Sep 15, 2023 1:21 pm

Chris Peterson wrote: Fri Sep 15, 2023 1:18 pm
johnnydeep wrote: Fri Sep 15, 2023 12:20 pm
Chris Peterson wrote: Thu Sep 14, 2023 9:30 pm

Actually, it would be Teel.
Yeah, not getting that one either.
"7331" is how you write "TEEL" in Leet.
Sure, but what does "teel" or "leet" have to do with this galaxy?
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Re: APOD: NGC 7331 and Beyond (2023 Sep 14)

Post by Chris Peterson » Fri Sep 15, 2023 1:23 pm

johnnydeep wrote: Fri Sep 15, 2023 1:21 pm
Chris Peterson wrote: Fri Sep 15, 2023 1:18 pm
johnnydeep wrote: Fri Sep 15, 2023 12:20 pm

Yeah, not getting that one either.
"7331" is how you write "TEEL" in Leet.
Sure, but what does "teel" or "leet" have to do with this galaxy?
It's NGC 7331.
Chris

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Re: APOD: NGC 7331 and Beyond (2023 Sep 14)

Post by johnnydeep » Fri Sep 15, 2023 1:47 pm

Chris Peterson wrote: Fri Sep 15, 2023 1:23 pm
johnnydeep wrote: Fri Sep 15, 2023 1:21 pm
Chris Peterson wrote: Fri Sep 15, 2023 1:18 pm
"7331" is how you write "TEEL" in Leet.
Sure, but what does "teel" or "leet" have to do with this galaxy?
It's NGC 7331.
Oh man, do I feel like a compleet fool now. (Skulking away in utter shame...)
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Re: APOD: NGC 7331 and Beyond (2023 Sep 14)

Post by Cousin Ricky » Fri Sep 15, 2023 2:59 pm

Chris Peterson wrote: Thu Sep 14, 2023 9:30 pm
johnnydeep wrote: Thu Sep 14, 2023 9:06 pm
Cousin Ricky wrote: Thu Sep 14, 2023 8:45 pm I wonder if anyone has dubbed this the Leet Galaxy.
I don't get it. :?
Actually, it would be Teel.
Not if you use a star diagonal.

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Re: APOD: NGC 7331 and Beyond (2023 Sep 14)

Post by Chris Peterson » Fri Sep 15, 2023 3:11 pm

Cousin Ricky wrote: Fri Sep 15, 2023 2:59 pm
Chris Peterson wrote: Thu Sep 14, 2023 9:30 pm
johnnydeep wrote: Thu Sep 14, 2023 9:06 pm

I don't get it. :?
Actually, it would be Teel.
Not if you use a star diagonal.
Depends on how many other mirrors you have in your system...
Chris

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