Image Credit & Copyright: Tom Matheson.
So here’s post 3-3 for the “Galaxies Under Hoof” series and hopefully by looking at this incredible image you now get the “ZOOM” thing as we’re taking two locations (the previous two images), detailed them both and now we zoom out to have a look at both of them, together in one relatively small patch of sky under the front legs of Pegasus (The Winged Horse). So let’s have a look at this region and both of these galaxy groups amazingly in one single image as they are on the night sky. In the process I will highlight a recurring problem that to me that just doesn’t sit well.
Out first image was the Deer Lick Group of Galaxies with its most prominent member, NGC 7331 which is the large blue spiral galaxy roughly 50 million light years away at upper right. Its four major counterparts, which are just fuzzy points of light in this image, are a mind bending ten times further away approximately.
At bottom left is another amazing sight; Stephen’s Quintet which we detailed in the last image that I posted before this one. This tight line of sight grouping of five galaxies brings the total number of major players in these two groups in a single small patch of sky to ten. That’s some perspective for the week, trillions of stars, hundreds of billions, possibly even trillions of planets seen as they were; some of them upwards of over 200 million years ago. All within a patch of sky that’s slightly larger than the full moon…..amazing.
So you want to hear my problem? Ok so here goes. The big blue galaxy in this image (NGC 7331) is 40-50 million light years away while the major interacting galaxies in Stephan’s Quintet are 260-290 million light years away and the blue upper left galaxy in the quintet (NGC 7320) is cataloged as being a foreground galaxy around 40-50 million light years away. Problem number one; it doesn’t seem that the large blue galaxy at the right of this image (NGC 7331) is the same distance away as the blue foreground galaxy in the quintet (NGC 7320). Problem number two; take a look back at the previous image, of the quintet. I’m supposed to be ok thinking that blue galaxy is 40-50 million light years away (some say even 30) and the others are at least 220 million plus light years beyond that? Seems off to me so NGC 7320 must be one of the smallest spiral galaxies I’ve ever seen or there’s something wrong with the distance estimates. This isn’t a big deal, just something that really bothers me as it never seems to be a concern anywhere I read about the group. My solution to these two problems; old blue in the quintet (NGC 7320) is more like 140 million light years distant, not 30-50 million. I could very well be wrong, any opinions?
Tom Matheson Astrophotography: http://www.guidescope.net/galaxies/stephan-deer.htm