NIHAO-UHD: The properties of MW-like stellar disks in high resolution cosmological simulations

Abstract

Simulating thin and extended galactic disks has long been a challenge in computational astrophysics. We introduce the NIHAO-UHD suite of cosmological hydrodynamical simulations of Milky Way mass galaxies and study stellar disk properties such as stellar mass, size and rotation velocity which agree well with observations of the Milky Way and local galaxies. In particular, the simulations reproduce the age-velocity dispersion relation and a multi-component stellar disk as observed for the Milky Way. Half of our galaxies show a double exponential vertical profile, while the others are well described by a single exponential model which we link to the disk merger history. In all cases, mono-age populations follow a single exponential whose scale height varies monotonically with stellar age and radius. The scale length decreases with stellar age while the scale height increases. The general structure of the stellar disks is already set at time of birth as a result of the inside-out and upside-down formation. Subsequent evolution modifies this structure by increasing both the scale length and height of all mono-age populations. Thus, our results put tight constraints on how much dynamical memory stellar disks can retain over cosmological timescales. Our simulations demonstrate that it is possible to form thin galactic disks in cosmological simulations provided there are no significant stellar mergers at low redshifts. Most of the stellar mass is formed in-situ with only a few percent ( ∼ < 5%) brought in by merging satellites at early times. Redshift zero snapshots and halo catalogues are publicly available.

The formation times and building blocks of Milky Way-mass galaxies in the FIRE simulations

“…The median cumulative in-situ fraction at z = 0 is ∼ 93 per cent, which is consistent with previous results in Anglés-Alcázar et al (2017), who analyzed the FIRE-1 simulations (including a version of m12i) and found that in-situ star formation dominates ≥ 95 per cent of the stellar mass growth at MW masses. The NIHAO simulations also show similar in-situ fractions (Buck et al 2019b).…”

“…Most simulations of MW/M31-mass galaxies, either idealized or cosmological focus on a single isolated galaxy/halo (e.g. AU-RIGA, NIHAO, ERIS, Caterpillar), not in a Local Group (LG)-like MW+M31 pair (Grand et al 2017;Buck et al 2019a;Guedes et al 2011;Griffen et al 2016). Exceptions include the ELVIS DM-only (DMO) simulation suite, which include 24 MW/M31-mass halos in LG-like pairs and a massmatched sample of 24 isolated halos (Garrison-Kimmel et al 2014), and the cosmological baryonic simulations of LGlike pairs from the APOSTLE suite (Sawala et al 2016).…”

The origin of metal-poor stars on prograde disc orbits in FIRE simulations of Milky Way-mass galaxies

“…Recently, Sestito et al (2021) performed a similar study as ours using 5 of the NIHAO-UHD cosmological zoom-in simulations of MW-mass galaxies (Buck et al 2020). Building on their previous work, they found that the simulated galaxies also show a prevalence for a prograde bias.…”

The artemis simulations: stellar haloes of Milky Way-mass galaxies

“…These simulations are run with the same hydrodynamical simulation code used for the EAGLE project (Schaye et al 2015;Crain et al 2015), but applied here at significantly improved spatial and mass resolution, using the zoomin technique (see below). The resolution of ARTEMIS is similar to other very recent high-resolution, hydrodynamical simulations of the Milky Way-analog haloes (Sawala et al 2016;Grand et al 2017;Garrison-Kimmel et al 2018;Buck et al 2020), making possible the study of the structural properties of stellar haloes of individual galaxies and more detailed comparisons with the observational data. Our sample of simulated galaxies is purely selected by halo mass and is larger than previous samples simulated at this resolution, providing a more diverse ensemble of merger histories that are compatible with the emergence of a Milky Way-like galaxy disc.…”