Kavli Affiliate: Tom Abel
| First 5 Authors: Minyong Jung, Ji-hoon Kim, Thinh H. Nguyen, Ramon Rodriguez-Cardoso, Santi Roca-Fàbrega
| Summary:
We investigate how differences in the stellar feedback produce disks with
different morphologies in Milky Way-like progenitors over 1 $leq z leq 5$,
using eight state-of-the-art cosmological hydrodynamics simulation codes in the
textit{AGORA} project. In three of the participating codes, a distinct,
rotation-dominated inner core emerges with a formation timescale of $lesssim
300$ Myr, largely driven by a major merger event, while two other codes exhibit
similar signs of wet compaction — gaseous shrinkage into a compact starburst
phase — at earlier epochs. The remaining three codes show only weak evidence
of wet compaction. Consequently, we divide the simulated galaxies into two
groups: those with strong compaction signatures and those with weaker ones.
Galaxies in these two groups differ in size, stellar age gradients, and
disk-to-total mass ratios. Specifically, codes with strong wet compaction build
their outer disks in an inside-out fashion, leading to negative age gradients,
whereas codes with weaker compaction feature flat or positive age gradients
caused primarily by outward stellar migration. Although the stellar half-mass
radii of these two groups diverge at $z sim 3$, the inclusion of dust
extinction brings their sizes and shapes in mock observations closer to each
other and to observed galaxies. We attribute the observed morphological
differences primarily to variations in the stellar feedback implementations —
such as delayed cooling timescales, and feedback strengths — that regulate
both the onset and duration of compaction. Overall, our results suggest that
disk assembly at high redshifts is highly sensitive to the details of the
stellar feedback prescriptions in simulations.
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