The Army of Tennessee was the main Confederate Army between Virginia and the Mississippi. The 4th Ky was part of the "Orphan" Brigade and you can find out about it's history here
http://www.rootsweb.ancestry.com/~orphanhm/index.html
Including a picture and entire page that I believe is your ancestor Alfred Cullen Thomas
http://www.rootsweb.ancestry.com/~orphanhm/thomas.htm

Ray