2006/08/01 by Simon P. Driver, Jochen Liske, Alister W. Graham
Physics and Astronomy · #Accretion (finance) #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Bimodality #Elliptical galaxy #Galaxies: Formation, Evolution, Phenomena #Galaxy #Interacting galaxy #Irregular galaxy #Lenticular galaxy #Luminosity #Spiral galaxy #astro-ph
paper · pdf · doi:10.1017/s1743921306004960
published in Proceedings of the International Astronomical Union 2(S235), 17-18 (Cambridge University Press) · Contribution to IAU S235 proceedings on Galaxy Evolution Across Hubble Time, Eds F.Combes & J.Palous, two pages
openalex publication_date 2006/08/01 · arxiv created 2006/10/25 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Abstract Galaxy bimodality is caused by the bulge-disc nature of galaxies as opposed to two distinct galaxy classes. This is evident in the colour-structure plane which clearly shows that elliptical galaxies (bulge-only) lie in the red compact peak and late-type spiral galaxies (disc-dominated) lie in the blue diffuse peak. Early-type spirals (bulge plus disc systems) sprawl across both peaks. However after bulge-disc decomposition the bulges of early-type spirals lie exclusively in the red compact peak and their discs in the blue diffuse peak (exceptions exist but are rare, e.g., dust reddened edge-on discs and blue pseudo-bulges). Movement between these two peaks is not trivial because whilst switching off star-formation can transform colours from blue to red, modifying the orbits of ~1 billion stars from a planar diffuse structure to a triaxial compact structure is problematic (essentially requiring an equal mass merger). We propose that the most plausible explanation for the dual structure of galaxies is that galaxy formation proceeds in two stages. First an initial collapse phase (forming a centrally concentrated core and black hole), followed by splashback, infall and accretion (forming a planar rotating disc). Dwarf systems coule perhaps follow the same scenario but the lack of low luminosity bulge-disc systems would imply that the two components must rapidly blend to form a single flattened spheroidal system.