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18 April 2024 |
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The role of mergers and halo spin in shaping galaxy morphology | | Vicente Rodriguez-Gomez
; Laura V. Sales
; Shy Genel
; Annalisa Pillepich
; Jolanta Zjupa
; Dylan Nelson
; Brendan Griffen
; Paul Torrey
; Gregory F. Snyder
; Mark Vogelsberger
; Volker Springel
; Chung-Pei Ma
; Lars Hernquist
; | | Date: |
29 Sep 2016 | | Abstract: | Mergers and the spin of the dark matter halo are factors traditionally
believed to determine the morphology of galaxies within a $Lambda$CDM
cosmology. We study this hypothesis by considering approximately 18,000 central
galaxies at $z=0$ with stellar masses $M_{ast} > 10^{9} , {
m M}_{odot}$
selected from the Illustris cosmological hydrodynamic simulation. The fraction
of accreted stars -- which measures the importance of massive, recent and dry
mergers relative to in situ star formation -- increases steeply with galaxy
stellar mass, from less than 5 per cent in dwarfs to 80 per cent in the most
massive objects, and the impact of mergers on galaxy morphology increases
accordingly. For galaxies with $M_{ast} > 10^{11} , {
m M}_{odot}$, mergers
have the expected effect: if gas-poor they promote the formation of spheroidal
galaxies, whereas gas-rich mergers favour the formation and survivability of
massive discs. This trend, however, breaks at lower masses. For objects with
$M_{ast} < 10^{11} , {
m M}_{odot}$, mergers do not seem to play any
significant role in determining the morphology, with accreted stellar fractions
and mean merger gas fractions that are indistinguishable between spheroidal and
disc-dominated galaxies. On the other hand, halo spin correlates with
morphology primarily in the least massive objects in the sample ($M_{ast} <
10^{10} , {
m M}_{odot}$), but only weakly for galaxies above that mass. Our
results support a scenario where (1) mergers play a dominant role in shaping
the morphology of massive galaxies, (2) halo spin is important for the
morphology of dwarfs, and (3) the morphology of Milky Way-sized objects, at the
transition between these two regimes, shows little dependence (at least in a
straightforward way) on galaxy assembly history or the angular momentum content
of the dark matter halo. | | Source: | arXiv, 1609.9498 | | Services: | Forum | Review | PDF | Favorites | |
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