May I ask from the linear control theory community whether the solution of the following problem are available in the literature?

My system is $ E \dot x=Ax+Bu$ , $ E,A$ are $ m\times n$ , $ m\ne n$ matrices and there is no special assumption is made on the $ \lambda E-A$ matrix pencil.

1. Detectability is necessary but not sufficient condition for the existence of Luenberger observer.

2. Causal Detectability is necessary and sufficient condition for the existence of Luenberger observer.

It will be great if I get some references/texts regarding these observer design line which shows the light on my asked questions. Thanks for helping.