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Abstract The structure of spiral galaxies is essential to understanding the dynamics and evolution of disk galaxies; however, the precise nature of spiral arms remains uncertain. Two challenges in understanding the mechanisms driving spirals are how galactic environment impacts spiral morphology and how they evolve over time. We present a catalog characterizing the properties, dynamics, and evolution ofm= 2 spiral structure in 10 Milky Way–mass galaxies from the FIRE-2 cosmological zoom-in simulations. Consistent with previous literature, we find that FIRE-2 spirals are transient, recurring features simultaneously present in the disk at varying pattern speeds (Ωp) that broadly decrease with radius. These spirals persist on gigayear timescales (mean duration of 1.90 Gyr), but fluctuate in amplitude on timescales of hundreds of millions of years. Tidal interactions and bar episodes impact the resultingm= 2 spiral structure: strong satellite interactions generally produce shorter-lived, stronger spirals with larger radial extent, and bars can increase Ωp. Galactic environment influences spiral structure, in which kinematically colder disks can support longer-lived, stronger spirals. The properties of identified spirals in FIRE-2 vary widely in radial extent (0.3–10.8 kpc), duration (1.00–6.00 Gyr), and amplitude (a2,max= 0.018–0.192). We find the presence of spirals in all age populations, suggesting these are density-wave-driven features. This work represents the first time that spiral structure has been cataloged in this manner in cosmological simulations; the catalog can be leveraged with current and forthcoming observational surveys, enabling systematic comparisons to further our understanding of galaxy evolution.
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This content will become publicly available on January 22, 2027
How mergers and flybys shape azimuthal age patterns in spiral galaxies
ABSTRACT Spiral structures are one of the most common features in galaxies, yet their origins and evolution remain debated. Stellar age distributions offer crucial insights into galaxy evolution and star formation, though environmental effects can obscure the intrinsic age patterns. Using the Auriga cosmological gravo-magnetohydrodynamical zoom-in simulations, we investigate the azimuthal age distribution of young stars ($${<} 2$$ Gyr) in a sample of five Milky Way-mass spiral galaxies over the past 5 Gyr. We quantify the age gradients across spiral arms using the mean age offset ($$\mathrm{\Delta \tau }$$) and the non-overlap fraction ($$f_{\mathrm{non{\text{-}}overlap}}$$). We further analyse the impact of mergers and fly-by events on the age gradients. Our results show that Auriga spiral galaxies generally feature younger stars in their leading edges compared to the trailing edges, with a typical $$\mathrm{\Delta \tau }$$ between 30 and 80 Myr. However, gas-rich interactions can disrupt this age offset, resulting in similar age distributions on each side of the spiral arms. In three snapshots, we observe similar mean ages on both sides of spiral arms but differing age distribution broadness, coinciding with satellite interactions crossing the host galaxy’s disc plane. Our simulation data suggest that the typical azimuthal age variation recovers within $$\sim$$600 Myr after galaxy interactions. This work highlights the transient role of environmental interactions in shaping spiral arm age patterns.
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- Award ID(s):
- 2421782
- PAR ID:
- 10705072
- Publisher / Repository:
- Monthly Notices of the Royal Astronomical Society
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 546
- Issue:
- 2
- ISSN:
- 0035-8711
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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