Bulge n and B/T in High Mass Galaxies: Constraints on the Origin of Bulges in Hierarchical Models
Jul, 2008Citations per year
Abstract: (arXiv)
We perform 2D bulge-disk and bulge-disk-bar decomposition on H-band images of 146 bright (M_B<-19.3), high mass, moderately inclined spirals from the OSU Bright Spiral Galaxy Survey. Our results are: (1) Our H-band bar fraction is ~58%, consistent with that from ellipse fits. (2) 70% of the stellar mass is in disks, 10% in bars, and 20% in bulges. (3) A large fraction (60%) of bright spirals have low n<=2 bulges. Such bulges exist in barred and unbarred galaxies across all Hubble types/ most have B/T<=0.2. Only 5% of bright spirals have bulges with n>=4 and B/T>0.2. (4) About 64% (68%) of massive spirals with n<=2 (B/T<=0.2) bulges host bars. Thus, bars may be important in building such bulges. (5) We compare bulge B/T and n in massive spirals with predictions from a set of Lambda CDM models. In the models, a bulge with B/T<=0.2 can exist in a galaxy with a past major merger if the last major merger occurred at z>2. The fraction of massive spirals which have past major mergers and host present-day B/T<=0.2 bulges is over 15 times smaller than the observed fraction (~66%) of B/T<=0.2. Thus, contrary to common perception, bulges built via major mergers fail to account for most B/T<=0.2 bulges present in 60% of massive spirals. Such bulges exist in systems with only past minor mergers, but no major mergers. These bulges can be built via minor mergers and secular processes. We explore one model focusing on bulges built via satellite stars in minor mergers, finding good agreement with observations. Future models will explore the role of secular processes.References(119)
Figures(27)