Hostname: page-component-cd9895bd7-gvvz8 Total loading time: 0 Render date: 2024-12-25T05:19:32.228Z Has data issue: false hasContentIssue false

The hierarchical build-up of bulges in CDM

Published online by Cambridge University Press:  01 July 2007

Sadegh Khochfar*
Affiliation:
Sub-Department of Astrophysics, University of Oxford, Denys Wilkinson Bldg., Keble Road, OX1 3RH, Oxford, U.K. email: [email protected]
Rights & Permissions [Opens in a new window]

Abstract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

We investigate the hierarchical build-up of stars in bulges within the standard Λ-cold dark matter scenario. By separating the population into stars born during starbursts that accompany the formation of spheroids in major mergers (starburst component), and stars that are previously formed in discs of progenitor galaxies (quiescent component) and added to the spheroid by dynamical interaction. Our results are summarised as follows: bulges that form early have larger starburst fraction and hence should be smaller than their counter parts that form later. The quiescent fraction in bulges is an increasing function of bulge mass, becoming constant at Mq/Mbul ~ 0.8, mainly due to the infall of satellite galaxies that contribute disc stars to the bulge. Minor mergers are an order of magnitude more frequent than major mergers and must play a significant role in the evolution of bulges. Above the critical mass Mc ~ 3 × 1010 M most of the stars in the universe are in spheroids, which at high redshift are exclusively elliptical galaxies and at low redshifts partly bulges. Due to the enhanced evolution of galaxies ending up in high density environments, the starburst fraction and the surface mass densities of bulges below Mc should be enhanced with respect to field galaxies. Dissipation during the formation of massive bulges in present day early-type spirals is less important than for the formation of present day elliptical galaxies of the same mass thereby explaining the possible difference in phase-space densities between spiral galaxies and elliptical galaxies.

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2008

References

Barnes, J. E. & Hernquist, L. 1992, Ann. Rev. of Astronomy and Astrophysics 30, 705CrossRefGoogle Scholar
Carlberg, R. G. 1986, ApJ 310, 593CrossRefGoogle Scholar
Jesseit, R., Naab, T., & Burkert, A. 2005, MNRAS, 360, 1185CrossRefGoogle Scholar
Jesseit, R., Naab, T., Peletier, R. F., & Burkert, A. 2007, MNRAS, 376, 997CrossRefGoogle Scholar
Kauffmann, G., Colberg, J. M., Diaferio, A., & White, S. D. M. 1999, MNRAS, 303, 188CrossRefGoogle Scholar
Khochfar, S. & Burkert, A. 2001, ApJ 561, 517CrossRefGoogle Scholar
Khochfar, S. & Burkert, A. 2003, ApJL 597, L117CrossRefGoogle Scholar
Khochfar, S. & Burkert, A. 2005, MNRAS 359, 1379CrossRefGoogle Scholar
Khochfar, S. & Silk, J. 2006a, MNRAS, 370, 902CrossRefGoogle Scholar
Khochfar, S. & Silk, J. 2006b, ApJL, 648, L21CrossRefGoogle Scholar
Khochfar, S. & Burkert, A. 2006, A&A 445, 403Google Scholar
Khochfar, S. & Ostriker, J. P. 2007, ArXiv e-prints, 704, arXiv:0704.2418Google Scholar
Naab, T. & Burkert, A. 2003, ApJ 597, 893CrossRefGoogle Scholar
Naab, T., Jesseit, R., & Burkert, A. 2006, MNRAS, 372, 839CrossRefGoogle Scholar
Naab, T., Khochfar, S., & Burkert, A. 2006, ApJL, 636, L81CrossRefGoogle Scholar
Sarzi, M., Rix, H.-W., Shields, J. C., Rudnick, G., Ho, L. C., McIntosh, D. H., Filippenko, A. V., & Sargent, W. L. W. 2001, ApJ, 550, 65CrossRefGoogle Scholar
Schawinski, K., et al. 2006, Nature, 442, 888CrossRefGoogle Scholar
Somerville, R. S. & Kolatt, T. S. 1999, MNRAS 305, 1CrossRefGoogle Scholar
Springel, V. & Hernquist, L. 2005, ApJL 622, L9CrossRefGoogle Scholar
Toomre, A. & Toomre, J. 1972, ApJ 178, 623CrossRefGoogle Scholar