$G_\delta$ covers of compact spaces

Abstract

We solve a long standing question due to Arhangel'skii by constructing a compact space which has a $G_\delta$ cover with no continuum-sized ($G_\delta$)-dense subcollection. We also prove that in a countably compact weakly Lindel\"of normal space of countable tightness, every $G_\delta$ cover has a $\mathfrak{c}$-sized subcollection with a $G_\delta$-dense union and that in a Lindel\"of space with a base of multiplicity continuum, every $G_\delta$ cover has a continuum sized subcover. We finally apply our results to obtain a bound on the cardinality of homogeneous spaces which refines De La Vega's celebrated theorem on the cardinality of homogeneous compacta of countable tightness.