Good question. There are two things to remember about St Thomas’ five ways. First of all, they are demonstrations of the reasonableness of faith. You cannot build a picture of the revealed God from the level of natural reason alone. In other words, we cannot establish God and all the Divine Names by moving from created effects to cause simply. The subject matter which examines ‘God’ is formally established only through Divine Revelation (ST Ia, q1. a4). So the five proofs, as St Thomas says clearly, are first and foremost about showing that faith is also reasonable and are what he calls ‘preambles’ to faith. To put it another way, you cannot argue or reason your way through natural reason to all the same conclusions provided for by Revelation. Natural reason for example could never arrive at knowledge of the Trinity unaided (Ia, q32, a1). So natural reason only takes us so far (Ia, q1, a1, ad4) but far enough for us to see that Revelation also makes sense to natural reason. Secondly, it is when we accept revelation that we see that what is revealed is also reasonable (ST Ia, q12, a12). What is revealed to us about God is able to be subject to reason and language (otherwise we could not know it).
That said however, we can make great progress with the nature of the Unmoved Mover using natural reason. We can also, by extension, come to understand the First Mover is good, one, infinite and intelligent (SCG, Bk 1, 41-44). Since we ourselves are intelligences, it follows that the cause of intelligence must itself be intelligent since no effect can be greater than its cause. Furthermore, an unmoved mover must be unmoved absolutely; that is, it cannot move ‘randomly’, since then it is subject to a motion outside of itself. It’s own motion must therefore be self-directed. So an energy force field doesn’t quite cut it as a proper designation for a first Necessary and Efficient Cause.
So in a nutshell, Aquinas does not make a leap from Unmoved Mover to the God of Christianity. He moves from the five ways to the intelligence and goodness of God, then on to God as revealed. The two positions cohere.