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NGC 253 + 1,800 galaxies + 19 quasars + 2 globular clusters

And now for something a little different...I just finished my first pass at processing the NGC 253 data from the TOA-150 system in Chile and annotated it using some software I wrote myself.  My program downloads information from both NED and SIMBAD for all the objects that those (quite comprehensive) databases know about, within the confines of our image frame, and labels each object with its name, magnitude, and (where available) distance.  I've attached the annotated image to this post.  There are 1800 annotated galaxies (155 having a known redshift, from which a distance can be computed, and 1645 without a known redshift), 19 quasars (all with a known redshift), and 2 globular clusters (which are not in our galaxy, but in NGC 253 itself).

A few notes on the annotations:

Make sure to view the image at 100% or the annotations may not be readable.

The long labels consist of the object name followed by the magnitude (to 1 decimal place) followed by its "light-travel-time distance" in millions of light years or billions of light years (if there's a "b" on the end).  There are dozens of useful ways of defining cosmological distances but I picked LTT as a simple, easy-to-grasp (for me at least) one.  LTT is simply the amount of time that light from the object has traveled to reach us.  The edge of the visible universe has a light travel time of about 13.8 BLy, so this can be easily compared to an object's LTT to give an idea of how close to the "edge" of the universe an object is.  The most distant object in the image we've captured is quasar "LQAC 12-024 001", labeled in cyan color near the bottom edge, toward the right, at magnitude 18.9 with a redshift of z = 4.15, which equates to a LTT of 12.2 BLy.

Yellow labels are galaxies with a known redshift, cyan labels are quasars, dim gray labels consisting of just a number (which is the object's magnitude) are galaxies without a known redshift, and red labels are globular clusters (both in NGC 253 itself).

Labels are just to the right of the center of each object, except near the right edge where a few labels are on the left (these are indicated by a short horizontal line to the right of the label pointing at the object).

I haven't implemented any sort of "map-makers algorithm" yet to avoid labels overlapping other labels.  Sorry about that, but luckily there aren't too many places where the labels are too crowded.  The worst offender is the clump of galaxies at the lower edge toward the right.

Almost all labeled objects are actually visible in the image, but you'll find some that are not.  I suspect in most cases the explanation is an error in the NED data, not a fault with our image.  Most of the problematic ones are galaxies with no redshift.

I imposed a cutoff of magnitude < 21 on the annotated objects.  There are several objects with magnitude 20.9 that are easily visible; an example is the quasar "LQAC 11-025 006" just to the upper left of NGC 253.

NED only provides redshift numbers so my program is responsible for converting from redshift to distance.  It does a good job except at very small redshifts, which is to be expected since there are different and better ways of computing distance for nearby galaxies.  So, for example, the value of 17 MLy for NGC 253 is wrong (it should be in the 11-12 range) but other than very close objects the LTT distance shown is pretty accurate.  An important though subtle detail is that I use the 5-year WMAP paramaters for converting from z to LTT, whereas the online NED portal by default uses the 3-year WMAP values.  (You can change them to 5-year if you know how, but probably no one bothers to do this.)  The 5-year WMAP values are the ones that correspond to the commonly-used 13.8 BLy age of the universe, so I thought it was worthwhile to match that model.

Hope you find this useful and interesting.

Mike Keith

Uploaded files:
  • ngc253-annotated.jpg

Wow, very interesting ! Do you have a link to a DL ? 🙂


Totally love the annotation capability. Great Job!

Any chance you will release it as a PI script or in some other form? I'd really like to try it. (Do you need a beta tester?)


JB & Alex,

Thanks for asking about the annotation program.  Some day I would like to release it for others to use but I'm afraid that's a pretty far off goal.  It's just needs the usual stuff: making it simpler to install and use, more rigorous testing, documentation, etc.  But realistically I won't be able to do that soon.  If/when I need beta testers I'll let you know.

For now I just wanted to show all the cool things we captured in the NGC 253 image.

Mike K.