Astronomy Observatory

"Pretty picture" processing of ASTR 310 images

Hi Elizabeth,

Over the break, I processed the data of the ASTR 310 targets into pretty pictures to share with the ASTR 310 students who wanted to see an alternate take on the data they collected and worked with. Since I found the quasar in the M74 image while doing this processing, I figured I may as well send them all along to you.

NGC 6946: Because two different groups observed NGC 6946 in slightly different filters, I combined their data to produce the attached image. Sloan g' images were mapped to the Blue channel of the photo, Sloan i' images were mapped to the Green channel of the photo, and H-alpha images were mapped to the red channel of the photo. This ordering is somewhat backwards, as the Sloan i' filter lets through longer wavelengths of light than H-alpha, so very red objects will appear green rather than red, but it does mean that the star-forming regions in NGC 6946 show the red glow of H-alpha.
There are loads of distant galaxies visible if you look carefully. The most distant one I was able to find a distance for using NED was WISEA J203310.25+600031.3, at approximately 3.3 Gly away. This galaxy is a faint green blob in the lower right of the image (directly left of the barred spiral galaxy). Also, if you are wondering why I kept the magenta bottom of the image rather than cropping it out, it's because there are a couple of very green galaxies in the lower left corner of the image.

NGC 7331: Sloan r' images have been mapped to yellow in the picture, and Sloan g' images have been mapped to blue.
My favorite part about this image is the dozens of galaxies other than NGC 7331 visible in the background. In addition to the galaxy by itself, I am also attaching a marked-up image that shows 22 other galaxies annotated. These were just the brighter galaxies in the area; however, there are loads more visible than what were annotated. I haven't checked, but I wouldn't be surprised if there is at least one galaxy that has a distance measured in billions of light-years, rather than the tens to hundreds of millions of light-years that many of these galaxies are.

M 74: Sloan r' images have been mapped to red in the picture, and Sloan g' images have been mapped to Cyan.
My favorite part about this image is all the galaxies other than M74 that are visible in the background. In addition to the galaxy by itself, I am also attaching a marked-up image that shows the locations of 47 other galaxies annotated. We are fortunate enough that this section of the sky was part of the Sloan Digital Sky Survey, so there are dozens of distant galaxies annotated, many of which are too faint to be detected with this dataset. There are, however, still a few galaxies that weren't annotated.

This image may potentially now hold the record for the most distant object seen by the UMD observatory, as quasar SDSS J013759.15+154438.1 can be seen to the left of the image, with a redshift of z = 3.63, which corresponds to a light travel time of approximately 11.5 billion years. I did confirm that SDSS J013759.15+154438.1 had a statistically significant detection (7.9 standard deviations above noise).
 
 

M 27: [O III] images have been mapped to cyan in the picture, and H-alpha images have been mapped to red.
In addition to the white dwarf visible in the center of the nebula, I think it's neat how you can see a bit of the outer oxygen shell of the planetary nebula in the lower-left corner of the image. The full extent of the nebula goes somewhat beyond what this image shows and has a rather interesting shape, but you'd need the wider FOV of the 7" to really see it.

NGC 1023: Sloan r' images have been mapped to red, Sloan g' images have been mapped to blue, and the average of r' and g' images has been mapped to green.
This target is interesting in that it is actually made up of two different galaxies, somewhat overlaid on each other. The main galaxy, NGC 1023, is the large, red, lenticular galaxy in the center of the image, but there is also NGC 1023A, which is apparently a satellite galaxy of NGC 1023 off to the left of the image, which is somewhat more blue than NGC 1023. There also seems to be different 'tidal shells' in NGC 1023 where there are steps in the galaxy's brightness; maybe due to past gravitational interactions with its satellites?
Unfortunately, I was not able to fully remove some of the flat artifacts. Based on some of the behavior we observed at the beginning of the semester, we believe this is caused in part by the filter wheel no longer returning to the same exact spot after switching to a different filter. Only a subset of dust spots are impacted by this effect, and the majority are correctly calibrated out. This is good in that the majority of the dust spots are correctly calibrated out, but also annoying, since shifting the master flat image to correct for this dust spot would result in the rest of the dust spots becoming incorrectly corrected for.

NGC 520: Sloan r' images have been mapped to yellow, and Johnson-Cousins B images have been mapped to blue.
There was one dust spot that did not calibrate out completely; I was able to reduce how clearly it showed up in the final image by repeatedly fitting a model to the background and then subtracting it, but it still isn't perfect.

Cat's Eye Nebula:

Clear skies!
-Matthew