Chemodynamics of barred galaxies in cosmological simulations: On the Milky Way’s quiescent merger history and in-situ bulge

GRAND, R J J; GARGIULO, I; MONACHESI, A; TISSERA, P; FRAGKOUDI, F; BLÁZQUEZ-CALERO, G; MARINACCI, F; PEREZ, I; PAKMOR, R; GOMEZ, F; NESS, M K; WHITE, S D M

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2020 vol. 494 p. 5936 - 5960

0035-8711

We explore the chemodynamical properties of a sample of barred galaxies in the Aurigamagneto-hydrodynamical cosmological zoom-in simulations, which form boxy/peanut(b/p) bulges, and compare these to the Milky Way (MW). We show that the Aurigagalaxies which best reproduce the chemodynamical properties of stellar populationsin the MW bulge have quiescent merger histories since redshift z ∼ 3.5: their lastmajor merger occurs at tlookback > 12 Gyrs, while subsequent mergers have a stellarmass ratio of ≤1:20, suggesting an upper limit of a few percent for the mass ratio ofthe recently proposed Gaia Sausage/Enceladus merger. These Auriga MW-analogueshave a negligible fraction of ex-situ stars in the b/p region (< 1%), with flattened,thick disc-like metal-poor stellar populations. The average fraction of ex-situ stars inthe central regions of all Auriga galaxies with b/p?s is 3% ? significantly lower thanin those which do not host a b/p or a bar. While the central regions of these barredgalaxies contain the oldest populations, they also have stars younger than 5 Gyrs(>30%) and exhibit X-shaped age and abundance distributions. Examining the discsin our sample, we find that in some cases a star-forming ring forms around the bar,which alters the metallicity of the inner regions of the galaxy. Further out in the disc,bar-induced resonances lead to metal-rich ridges in the Vφ − r plane ? the longest ofwhich is due to the Outer Lindblad Resonance. Our results suggest the Milky Wayhas an uncommonly quiet merger history, which leads to an essentially in-situ bulge,and highlight the significant effects the bar can have on the surrounding disc.