Making matters confusing is the fact that the phrase "a young galaxy" is commonly used to refer to a galaxy formed when the universe was young – if it’s far awa

Making matters confusing is the fact that the phrase "a young galaxy" is commonly used to refer to a galaxy formed when the universe was young – if it’s far away (high redshift, z >> 1) and as such we see it the way it was when the universe was young! This specific study, however, looked for more nearby galaxies (z < 1, we see the light that was emitted a few billion years ago) so these galaxies (as we see them) are in fact "old". I think essentially all existing galaxies either formed >10 Gy ago or are the results of galaxy mergers – so in that sense there are no "young", recently-formed galaxies in the universe at all as the raw material was long ago used up. As such in astro-talk "young galaxies" can fairly unambiguously mean "far-away galaxies". But formally they’d be called high-z or high-redshift galaxies.