This poster is the 41st in my series of compilation posters.  All of these posters can be seen in my Astrobin Poster Collection.

This poster is a collection of anemic galaxies.  The term “anemic galaxy” was established in 1976 by the astronomer Sidney van den Bergh as an intermediate galaxy type between spiral galaxies and lenticular galaxies.

Spiral galaxies have lumpy white blotches, blue star clouds, and pink HII regions in the outer disk.  They generally have a large amount of gas which fuels star formation and shapes the structure of the spiral arms in the outer disk.

In anemic galaxies, the gas fuel for star formation has run out in the outer disk.  Anemic galaxies have distinct arms but the outer disk looks very smooth, as if someone has applied extreme noise reduction to them. They have almost no star formation occurring in the outer disk.  In time, scientists believe that an anemic galaxy loses its spiral character and transitions to a lenticular galaxy.

The first column of the poster contains 3 typical spiral galaxies, while the last column contains 3 lenticular galaxies.  In the center are 9 anemic galaxies, believed to be transitioning from spiral to lenticular form.

There is still a lot of uncertainty about these anemic galaxies.  In fact, I found numerous disagreements over the years about which galaxies are classified as anemic galaxies.  I selected the 9 anemic galaxies for the poster based on a consensus of various sources.

Like most classification systems, the classification of anemic galaxies was first focused on the visual element.  The issue with this is that factors such as distance and seeing affect our perception of the characteristic and appearance of a galaxy disk.  Recent attempts to quantify the anemic galaxy criteria in order to eliminate the subjective visual component have been met with limited mixed success so far.  

If you would like to see more detail on any of these anemic galaxies, each of them has previously been uploaded and described individually on Astrobin. I also have imaged 6 other anemic galaxies that are not included on the poster.  All 15 anemic galaxies reside in my Astrobin Anemic Galaxy Collection.