Journal Article

The size evolution of galaxy discs formed within Λ cold dark matter haloes

C. Firmani and V. Avila–Reese

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 396, issue 3, pages 1675-1681
Published in print July 2009 | ISSN: 0035-8711
Published online June 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.14844.x
The size evolution of galaxy discs formed within Λ cold dark matter haloes

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By means of galaxy evolutionary models, we explore the direct consequences of the Λ cold dark matter (ΛCDM) cosmogony on the size evolution of galactic discs, avoiding intentionally the introduction of intermediate (uncertain) astrophysical processes. Based on the shape of the rotation curves and guided by a simplicity criterion, we adopt an average galaxy mass baryon fraction fgal= 0.03. In order to study general behaviours, only models with the average initial conditions are analysed. The stellar and B–band effective radii, R and RB, of individual galaxies grow significantly with time (inside–out disc formation) with laws that are weakly dependent on stellar mass, M or luminosity, LB. However, the change of R with z at a fixedM is slow; for z≤ 2.5, R(M= constant) ∝ (1 +z)−0.4 for a large range of masses. On the other hand, the change of RB with z at a fixedLB is strong and it resembles the RB decreasing law of the individual models; roughly RB(LB= const) ∝ (1 +z)−0.85 for z≲ 0.75, and ∝ (1 +z)−1.1 for higher zs. We find also that at z= 0, RM0.38 and RBL0.40B, remaining the slopes of these relations practically the same up to z≈ 3. Our model predictions are in reasonable agreement with observational inferences on the typical radius change with z of late–type galaxies more luminous (massive) than high values imposed by the selection effects. The models also seem to be consistent, within the large scatter, with the RB and LB values obtained from small (non–complete) samples of sub–L late–type galaxies with available rest–frame photometric information at different zs. The properties and evolution of the ΛCDM haloes seem to be the main drivers of galaxy disk size evolution. Nevertheless, the models reveal a potential difficulty in explaining the observed steepening of the RBLB relation with respect to the RM one, an effect related to the well–established colour–magnitude relation.

Keywords: galaxies: evolution; galaxies: haloes; galaxies: high–redshift; galaxies: spiral; cosmology: theory

Journal Article.  5774 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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