Abstract. We prove that, in a triangulated category with combinatorial models, every localizing subcategory is coreflective and every colocalizing subcategory is reflective if a certain large-cardinal axiom (Vopěnka's principle) is assumed true. It follows that, under the same assumptions, orthogonality sets up a bijective correspondence between localizing subcategories and colocalizing subcategories. The existence of such a bijection was left as an open problem by Hovey, Palmieri and Strickland in their axiomatic study of stable homotopy categories and also by Neeman in the context of well-generated triangulated categories.
IntroductionThe main purpose of this article is to address a question asked in [37, p. 35] of whether every localizing subcategory (i.e., a full triangulated subcategory closed under coproducts) of a stable homotopy category T is the kernel of a localization on T (or, equivalently, the image of a colocalization). We prove that the answer is affirmative if T arises from a combinatorial model category, assuming the truth of a large-cardinal axiom from set theory called Vopěnka' More precisely, we show that, if K is a stable combinatorial model category, then every semilocalizing subcategory C of the homotopy category Ho(K) is coreflective under Vopěnka's principle, and the coreflection is exact if C is localizing. We call C semilocalizing if it is closed under coproducts, cofibres and extensions, but not necessarily under fibres. Examples include kernels of nullifications in the sense of [11] or [19] on the homotopy category of spectra.We also prove that, under the same hypotheses, every semilocalizing subcategory C is singly generated ; that is, there is an object A such that C is the smallest semilocalizing subcategory containing A. The same result is true for localizing subcategories. The