On concluding affine ness of a connected scheme from the existence of a proper monomorphism to an affine, Noetherian scheme of finite Krull dimension

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Let $X$ be a connected Scheme. Let $Y$ be an affine, Noetherian Scheme of finite Krull dimension. If there exists a proper morphism of schemes $X\to Y$ which is also a monomorphism in the category of schemes , then is $X$ necessarily affine ?

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Just to get this off the unanswered queue.

The point is that if $f:X\to Y$ is a morphism of arbitrary schemes, then $f$ is a closed embedding if and only if $f$ is a proper monomorphism. In fact, there are many equivalent definitions of closed embedding in a similar vein. See Tag04XV.

So, if $Y$ is any affine scheme and $X\to Y$ is a proper monomorphism, then $X$ is a closed subscheme of $Y$ and thus affine.