ner_tags: O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Wavelength I-Wavelength O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Formula I-Formula I-Formula O O O O O O O O O O O O B-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Formula I-Formula I-Formula O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Formula I-Formula I-Formula O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Formula I-Formula I-Formula O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O
tokens: drops (to 30%) in the lowest redshift bin. This decline may not be reliable for two reasons. First, the size of the star-forming sample at 0.5 z 1.0 is very small (only 10 objects), and therefore the sample proportions are not statistically significant. Second, the H -band images for the low- z objects are missing the bluer parts of the galaxy flux (see also Elmegreen Elmegreen 2014 ). Figure 9. Examples of galaxies with apparent spiral structures at different redshifts. The residual images, after removal of the bulge+disk model from the original galaxy image, allow for more effective detection of fine substructure. Table 5 Estimated Fraction of Massive Galaxies with a Prominent Stellar Disk Using Different Diagnostics Note. Column (1) Massive galaxies with bulge-to-total ratios less than 0.5. Column (2) Massive galaxies with visually detectable spiral structures. Column (3) Edge-on massive galaxies with e > 0.6. The conditions necessary for the formation of spiral arms are complex (see Dobbs Baba 2014 for a review), but one requirement is clear—the existence of a disk. Thus, from the point of view of one of the main themes of this paper, the clear detection of spiral features in high- z massive galaxies constitutes arguably the strongest, most model-independent evidence for the presence of a substantial disk component in these systems. We see the spiral features only in the star-forming galaxies and not in quiescent systems, but, by analogy with local S0 and spiral galaxies, this is not surprising. An edge-on view of a galaxy can reveal another indisputable signature of a prominent stellar disk. Figure 10 gives several examples of highly flattened ( e > 0.6) galaxies in our sample that are consistent with disk structures seen edge-on. Interestingly, most of them are relatively thick. The fraction of galaxies with a stellar disk can be inferred from the frequency of detected edge-on galaxies. For this estimation, we assume a uniform distribution of ellipticity with 0 e 0.8 for a population of bulge+disk systems. The inferred fraction of galaxies with a disk hovers around 40%–50% at 1.0 z 2.5, among both star-forming and quiescent galaxies, but the incidence of edge-on quiescent galaxies below z = 1 drops to zero (Table 5 ). Highly flattened systems (especially at high z ) can be hallmarks of a merger. However, considering the fact that the majority of these galaxies are compact, the chance of this degeneracy is low. Figure 10. Examples of massive galaxies with an edge-on disk at different redshifts. 5. Implications for Galaxy Evolution The discovery of red nuggets has captured much attention in recent years because it requires a new paradigm for the formation and evolution of massive elliptical galaxies. The observed compactness of red nuggets at z ≈ 2 initially raised the question of whether the massive red galaxies have indeed increased their sizes by a factor of roughly ∼3–5 while maintaining their passive state, or whether the size