Journal Article

The other side of bulge formation in a Λ cold dark matter cosmology: bulgeless galaxies in the local Universe

Fabio Fontanot, Gabriella De Lucia, David Wilman and Pierluigi Monaco

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 416, issue 1, pages 409-415
Published in print September 2011 | ISSN: 0035-8711
Published online August 2011 | e-ISSN: 1365-2966 | DOI: https://dx.doi.org/10.1111/j.1365-2966.2011.19047.x
The other side of bulge formation in a Λ cold dark matter cosmology: bulgeless galaxies in the local Universe

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We study the physical properties, formation histories and environment of galaxies without a significant ‘classical’ spheroidal component, as predicted by semi-analytical models of galaxy formation and evolution. This work is complementary to the analysis presented in De Lucia et al., where we focus on the relative contribution of various physical mechanisms responsible for bulge assembly in a Λ cold dark matter cosmology. We find that the fraction of bulgeless galaxies is a strong decreasing function of stellar mass: they represent a negligible fraction of the galaxy population with M > 1012 M, but dominate at M < 1010 M. We find a clear dichotomy in this galaxy population, between central galaxies of low-mass dark matter haloes and satellite galaxies in massive groups/clusters. We show that bulgeless galaxies are relatively young systems, that assemble most of their mass at low redshift, but they can also host very old stellar populations. Since galaxy–galaxy mergers are assumed to lead to the formation of a spheroidal component, in our models these galaxies form preferentially in low-mass haloes that host a small number of satellites galaxies. We show that the adopted modelling for galaxy mergers represents a key ingredient in determining the actual number of bulgeless galaxies. Our results show that these galaxies are not a rare population in theoretical models: at z ∼ 0, galaxies with no classical bulge (but often including galaxies with the equivalent of pseudo-bulges) account for up to 14 per cent of the galaxies with 1011 < M/M < 1012.

Keywords: galaxies: bulges; galaxies: evolution; galaxies: formation; galaxies: interactions; galaxies: structure

Journal Article.  5755 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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