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Paper: Properties and Origin of Bulges in High Mass Spirals
Volume: 419, Galaxy Evolution: Emerging Insights and Future Challenges
Page: 74
Authors: Weinzirl, T.; Jogee, S.; Khochfar, S.; Burkert, A.; Kormendy, J.
Abstract: The distributions of bulge-to-total mass ratio (B/T) and bulge Sérsic index n are quantified to explore the fundamental question of how bulges form. We perform 2D bulge-disk and bulge-disk-bar decomposition on H-band images of bright (MB ≤ –19.3), high mass (M* ≥ 1.0 × 1010 Msun), moderately inclined (i < 70°) spirals. A large fraction of high mass spirals (∼74%) have n ≤ 2 bulges, and 66% have B/T ≤ 0.2. Such low-B/T and low-index bulges exist in barred and unbarred galaxies across a wide range of Hubble types. We compare the results with predictions from a set ΛCDM-based galaxy formation models. The predicted fraction (∼1.6%) of high mass spirals with a past major merger since z ≤ 4 and a bulge with a present-day B/T ≤ 0.2 is over 30 times smaller than observed. The majority of B/T ≤ 0.2 bulges in high mass model galaxies exist in systems that have experienced only minor mergers, and no major mergers. Bulges built via major mergers seriously fail to account for the bulges present in most high mass spirals. Most bulges appear to be created by some combination of minor mergers, smooth accretion, and secular processes.
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