THE COSMOLOGICAL SIZE AND VELOCITY DISPERSION EVOLUTION OF MASSIVE EARLY-TYPE GALAXIES

By Ludwig Oser, T. Naab, Jeremiah P. Ostriker, Peter H. Johansson. 2011

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We analyze 40 cosmological re-simulations of individual massive galaxies with present-day stellar masses of M* > 6.3 × 1010 M☉ in order to investigate the physical origin of the observed strong increase in galaxy sizes and the decrease of the stellar velocity dispersions since redshift z ≈ 2. At present 25 out of 40 galaxies are quiescent with structural parameters (sizes and velocity dispersions) in agreement with local early-type galaxies. At z = 2 all simulated galaxies with M* ≳ 1011 M☉ (11 out of 40) at z = 2 are compact with projected half-mass radii of ≈0.77 (±0.24) kpc and line-of-sight velocity dispersions within the projected half-mass radius of ≈262 (±28) km s−1 (3 out of 11 are already quiescent). Similar to observed compact early-type galaxies at high redshift, the simulated galaxies are clearly offset from the local mass–size and mass–velocity dispersion relations. Toward redshift zero the sizes increase by a factor of ∼5–6, following R1/2∝(1 + z)α with α = −1.44 for quiescent galaxies (α = −1.12 for all galaxies). The velocity dispersions drop by about one-third since z ≈ 2, following σ1/2∝(1 + z)β with β = 0.44 for the quiescent galaxies (β = 0.37 for all galaxies). The simulated size and dispersion evolution is in good agreement with observations and results from the subsequent accretion and merging of stellar systems at z ≲ 2, which is a natural consequence of the hierarchical structure formation. A significant number of the simulated massive galaxies (7 out of 40) experience no merger more massive than 1:4 (usually considered as major mergers). On average, the dominant accretion mode is stellar minor mergers with a mass-weighted mass ratio of 1:5. We therefore conclude that the evolution of massive early-type galaxies since z ≈ 2 and their present-day properties are predominantly determined by frequent “minor” mergers of moderate mass ratios and not by major mergers alone.

Subfields: Astronomy and Astrophysics, Computer Vision and Pattern Recognition, Instrumentation

View Paper: https://www.semanticscholar.org/paper/12d82f26813e19550d2f402d52ea0d419a3fc32d

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Citations in the corpus

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Theoretical Challenges in Galaxy Formation (2016, result): “…is efficiently converted into stars, some of the systems can be remarkably small (also supported by mergers, Bournaud et al. 2011a, Wuyts et al. 2010), very similar to the population of observed high-redshift compact galaxies (Oser et al. 2012, 2010, Sommer-Larsen & Toft 2010, Wellons et al. 2016).”
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The CALIFA survey across the Hubble sequence: Spatially resolved stellar population properties in galaxies (2015, background): “Shallow metallicity gradients are expected if elliptical galaxies result from major mergers (e.g. Kobayashi 2004), but a minor merger picture for the formation of ellipticals can successfully explain the strong size evolution of massive galaxies (Oser et al. 2012).”
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