Single 15 minute raw frame of NGC4565 taken with the 16″ RiDK at OBRO (Orion’s Belt Remote Observatory). Green channel. It just happened that on this night we had the best seeing since my observatory went up 2+ years ago! The galaxy is slightly off center because that was where the best guide star was located. A typical satellite trail is to the upper left. Several small galaxies are seen in the lower part of the field (see below)
The well-known galaxy NGC 4565 or the “Needle Galaxy” is seen edge on from Earth at a distance of around 50 million light years. It is also a popular imaging target and so I am in the process of imaging it with the 16″ telescope at Orion’s Belt Remote Observatory What is not as well known are the thousands upon thousands of other objects that are also contained in this 45 arc minute square of space! This is not something I am discovering for the first time but since we had a superb night of seeing when this image was taken I decided to look a little more closely at the “background” of my image. I think this activity is very important in general for anyone imaging out there because you might surprise yourself with what you find. And to be fair, you never know if perhaps there is something”undiscovered” in your images! So the steps I take to uncover the “hidden gems” in my images are as follows:
- I take my image and open it in the program I use for image processing, i.e. Pixinsight
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Go to scripts> image analysis> imagesolver
Plate solve the image. To do that you do what it says in the caption and image above.
- After you run the script I just leave the image open and then go to the next step which is to run the annotation script. That’s the one that tells you what’s in there!
Under scripts go to the “render” category and then under that select “annotate image”
The result is seen below:
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NGC 4565 “and friends”. After running the annotate image script you see the grid and many named objects in there. This was actually the result of the second run of the annotation script. The first time some of the galaxies were unlabeled (see below).
Now let’s look a little more carefully at this:
A little more magnification shows there 5 obvious named galaxies but one I circled which was not named after I ran the script the first time.
The small fuzzy patch in the center here is not dust or some other artifact but is actually “IC3571”, an irregular galaxy. Quite dim. It is around magnitude 17-18. Remember this is a green filtered image so my guess is a lot more information would exist with an unfiltered exposure! As I look around the image I see all of the galaxies named are of the “IC” catalog type. This stands for “Index Catalog” and is a supplement apparently to the well known “NGC” catalog or “New General Catalog” which was produced at the end of the 19th century! Since then the explosion in data acquisition over just the last 20 years has produced countless catalogs and databases which we now have access to! So back to the image. I was very curious why the galaxy I circled in white in the 2nd image above was not designated as it was obviously brighter. I went back to the image annotation script and realized there was a galaxy catalog database that was not checked!
The “PGC Hyperleda” box was not checked the first time I ran the script
So what is this? “PGC” is the “Principal Galaxies Catalog” published in 1989. The “Lyon-Meudon” extragalactic database or “LEDA” was created at the Lyon observatory in France in 1983 and apparently the PGC catalog was based on LEDA. In the early 2000’s the PGC/LEDA database expanded to become “HyperLEDA” or literally LEDA on steroids! It’s basically an extragalactic database for astrophysical research and contains data on about 2 million galaxies! We’re light years away from the old “NGC” days!
After running the annotation script a second time with the PGC data included, the result was this:
After running the annotation script a second time with the PGC data included, the previously unknown galaxy is identified!
The galaxy I had circled in my original image that was unnamed is now identified as “PGC42060”!
More information about this region can be investigated on the HyperLEDA database website. That will keep you busy for awhile!:
But that’s not all! What else could be hiding in the background? You can also go to the well known astronomical database “Simbad”:
Simbad home page
You have a number of options from here. If you enter the name of the principal object in this case NGC4565 and the size of the field (50 arc min) you will arrive on a page with a list of hundreds of identifiable objects. Not only galaxies, but planetary nebulae as well! If you go to the top of the Simbad home page, you can click on the second tab to the right labeled “Aladin”. There you can access a digitized sky survey image of your field that shows you where all of these objects are located:
If you go to this page you can run the applet “Aladin Lite” in your browser. Type in the target name and an actual image will be generated with color coded dots all over the place showing you what objects are in the field!
And you thought this was just about “pretty pictures”! Enjoy hunting for the “hidden gems” in your images!
Thanks for reading!
Dr Dave
daveandtelescope 