Abell 2645: A distant but rich galaxy cluster

[Martin Meredith]

There are 195 Abell galaxy clusters in Aquarius alone. The richest (richness class 4 of 5, with more than 200 individual galaxies) is Abell 2645. It is also very distant (distance class 6 of 7), with a redshift of 0.25,  corresponding to a distance of just under 3 billion light years. I was interested to see how many of these galaxies it would be possible to detect using the methods of EEVA i.e. short subs, live stacking.

On the right is a shot taken with 48 x 15s subs, amounting to 12 minutes total exposure. The left shows the SDSS image of the same area. I had to apply an extreme stretch (of the form x / (x+small constant)) and invert the image to be able to see much at all and even then it wasn't obvious what were galaxies and what were clumps of statistical noise. But comparison with the DSS image shows quite a few member galaxies being picked up. There is a clear 'wishbone' or 'lambda' structure just NW of the cluster centre which shows up well, and a 'Cepheus' or 'monopoly house' shape just to the SE of centre that is clear on both images.

It is hard to find photographic or visual magnitudes for these galaxies (the brightest galaxy listed by LEDA is mag 18.9) and they mainly have listed mags for the ugriz bands, but I estimate they are mainly in the range 19-21 (B), and I'm probably missing some at the top part of this range.

 

 

These 'distant open clusters of the galaxy world' are amongst my favourite types of objects to observe. As I see the faint specks emerge in great numbers I imagine that each one may well be teeming with life in billions of individual systems, and this turns a barely-detectable signal in a few pixels into something else entirely.  

Details: Quattro 8" f/4 Newt on AZEq6 in alt-az mode, Lodestar X2 mono camera, SLL v3.3 for acquisition and Jocular for live stacking and processing. No darks nor flats. SQM 20.2.

Martin

 

 

[Mike JW]

Hi Martin,

You have set me thinking with this image as to what I might be able to locate. I have never really investigated the Abell Clusters - not enough time........ Mike