Is it possible to completely remove Android OS from Toshiba Tablet AT105 and boot it as Ubuntu?
The current development of Ubuntu for Android is focused on the Nexus 7 reference platform.
There may be a solution tailored for the Toshiba AT105 tablet ..
Check out XDA Developers forums: Welcome to xda-developers
These solutions are typically Android-based, and allow some form of Linux / Ubuntu to be installed. They may also require 'rooting' your device, ROM-BIOS updates, and/or customization.