Preface

After countless requests on how we stack data from multiple contributors and systems, we are happy to finally have published a full pre-processing tutorial on our website: Link
We hope that this helps other collaborations out there to go and do the same thing we are doing in the DSC, and/or help improve the workflow of existing methods!
A huge thank you to Carl Björk @Palmito and Sean Pickard @Sean who put together this amazing in-depth Tutorial!

Write-up

The Deer Lick group, a group of several galaxies, is located in the constellation of Pegasus. The biggest galaxy, NGC 7331, lies at a distance of roughly 45 million lightyears and spans some 120.000 ly in diameter. The other galaxies making up the Deer Lick group are smaller in size and lie at distances of 295-365 million lightyears from earth.
Besides the Deer Lick group, this picture also includes the famous Stephan’s Quintet, a grouping of 5 galaxies, of which 4 form the first compact galaxy group to ever be discovered in 1877, as well as other galaxies with prominent visual features, such as NGC 7315.
These various interesting galaxies, along with abundant IFN make this region a rather popular target for amateur photographers, with special focus on maximising detail in the Quintet and revealing all of the IFN.
Some unique attributes of the Quintet include prominent tidal streams, which are a result of the mutual interaction of the 4 galaxies, as well as the striking Ha regions of the fifth galaxy, NGC7320 which are a result of extensive star formation.
Looking at our DSC picture, the elephant in the room is the abundant and striking Ha emission in this region - back when we started this project in July of ‘24, no amateur images showcasing this background existed, making it even more appealing for us. In the meantime, several other astrophotographers also noted this Ha background and released their own renditions of it. More details on this Ha background will follow in the next section of the write-up.

Wanting to combine all of these awesome features into one image, our goal was set at roughly 240h of LRGB in a 5-1-1-1 split, as well as 150h of Ha, ensuring optimal signal and detail in all aspects covered above.
With the small FOV group of the DSC we started gathering data in late July and imaged for about 3 months, followed by 3 months of pre- and post-processing the data. We had a total of 12 people working on the project - 1 Editor, 1 Stacker , 11 photographers and myself coordinating (Stacker and myself also got data for the project) - in the end we managed to get a total of 580h13m of integration - exceeding our goals and marking the longest integration ever on this field.

Before getting into any details in the picture, I want to thank everybody who contributed to this project. It was a pleasure working together with everybody!

Tim Schaeffer - @Tim Schaeffer – Coordinator and Photographer
Adrien Keijzer - @Adrien Keijzer – Stacker and Photographer
Steeve Body - https://steevebody.com/ – Editor

And our photographers:
Akash Jain - @Meeps51
Mike Hamende - @Mike Hamende
Ryan Wierckx - @Ryan Wierckx
John Dziuba - @John Dziuba
Paul Kent - @Paul Kent
Bogdan Borz - @Bogdan Borz
Antoine and Dalia Grelin - www.galactic-hunter.com
Mark Petersen - @Mark Petersen
Jens Unger - @Jens Unger

Special thanks to:

Patrick Ogle, for being our science consultant and bringing up this target in the first place
Adrien, for stacking all of our nearly 3000 files and running extensive tests to find the best settings
Carl, for being our stacking consultant and helping out Adrien with some technical problems we ran into
Steeve, for another super impressive and well-rounded edit, making the most of our data.

Interesting features in our image

The Hydrogen alpha background

As noted in the introduction, one of the main reasons why we chose to image the Deer Lick region is the pronounced Ha background found in it, that, until recently, had never been photographed by amateurs. This Ha background was first brought to our attention by our science consultant Patrick Ogle, who first noted the Ha blowout/shockwave in his observations in August of 2020. A big thank you to Patrick for this suggestion, which directly led to the DSC image you see today!
To ensure maximal signal in the Ha, we used long sub-exposures, with an average of over 1400 seconds per sub. In doing so, and 880 subs later, we were able to gather a total of over 350 hours of data, giving us a high SNR stack to work with. The continuum subtracted H-alpha DSC stack can be found in the picture below.

© DSC -Continuum subtracted Ha in the Deer Lick region

What makes this Ha background so intriguing is the sharp shock-front that goes right through the middle of the frame, as well as the associated bulge of Ha on the right hand side. As such sharp lines generally do not belong to the galactic Ha cirrus, it is difficult to say what exactly the origin of this shock-front is. However, looking at the wide-field Ha data from Akash’s dataset below, it can be seen that the shock-front seems to be coming from the Great Lacerta Nebula (which is cut off to the left side of the frame) with Stellar winds possibly inflating this bubble - an explanation first proposed by Patrick Ogle.

© Akash Jain - Widefield Ha of the Deer Lick region

Full tidal stream and IFN

Another striking aspect of our image is the abundant IFN. As previous images of this region failed in revealing the full extent of the IFN, this made it the perfect challenge for us. So after gathering a total of over 130h of Luminance and over 90h RGB, we were indeed able to fully reveal all IFN in this region with great detail and signal. This, together with the H-alpha background adds to the immense dynamic of this image.
As a result of the many gathered hours in Broadband, we were also able to reveal the Quintet’s tidal streams, and even some colour in them, making them seem Blue-ish - characteristic for star-forming regions where most of the formed stars are extremely hot and hence emit white-blue light.
Both the IFN and the tidal streams can be seen in the picture below.

© DSC - Starless LRGB image showcasing the IFN in this region and a close-up of Stephan’s Quintet

Various galaxies

Finally, there’s the many other galaxies included in our framing. The most striking one probably being NGC 7315, which showcases a big halo. NGC 7315 itself is measured to be about 135kLys in diameter, while the inner halo, based on our data, measures some 200kLys and the potential outer halo a staggering 385kLys in diameter.
The annotated version highlighting the various potential halos can be found below.
Besides NGC 7315, there’s many other smaller galaxies in the framing that you can explore by going to our website and zooming into the full-resolution version hosted there!

© DSC - Close-up of NGC 7315 and annotations of its halos

For any further questions about the project, feel free to leave a reach out to us using the contact form or by leaving a comment!

If you want to see our image in greater detail, feel free to go to our gallery, where the image is uploaded in full resolution ( 6500 × 3677 px), enabling you to explore the picture by yourself and being able to zoom in on every tiny detail!
Link to our gallery: https://deepskycollective.com/gallery

Integration overview
Here you find a list of integration contribution from all 11 photographers

We hope that you enjoy this image!
Text written by @Tim Schaeffer , organiser and co-ordinator of the project.