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The Large Magellanic Cloud (LMC) will induce a dynamical friction (DF) wake on infall to the Milky Way (MW). The MW’s stellar halo will respond to the gravity of the LMC and the dark matter (DM) wake, forming a stellar counterpart to the DM wake. This provides a novel opportunity to constrain the properties of the DM particle. We present a suite of high-resolution, windtunnel-style simulations of the LMC's DF wake that compare the structure, kinematics, and stellar tracer response of the DM wake in cold DM (CDM), with and without self-gravity, versus fuzzy DM (FDM) withm_a= 10⁻²³eV. We conclude that the self-gravity of the DM wake cannot be ignored. Its inclusion raises the wake’s density by ∼10%, and holds the wake together over larger distances (∼50 kpc) than if self-gravity is ignored. The DM wake’s mass is comparable to the LMC’s infall mass, meaning the DM wake is a significant perturber to the dynamics of MW halo tracers. An FDM wake is more granular in structure and is ∼20% dynamically colder than a CDM wake, but with comparable density. The granularity of an FDM wake increases the stars’ kinematic response at the percent level compared to CDM, providing a possible avenue of distinguishing a CDM versus FDM wake. This underscores the need for kinematic measurements of stars in the stellar halo at distances of 70–100 kpc.

 

Abstract In addition to occupying the extreme, diffuse tail of the dwarf galaxy population, ultra-diffuse galaxies (UDGs) are themselves a key laboratory in which to study star formation in extreme low-density environments. In the second paper of this series, we compare the spatially resolved star formation activity of 22 H i -selected UDGs and 21 “normal” dwarf galaxies within 120 Mpc to predictions within the pressure-regulated, feedback-modulated (PRFM) theory of star formation. To do so, we employ a joint spectral energy distribution fitting method that allows us to estimate star formation rate and stellar mass surface density from UV-optical imaging. We find that the PRFM framework extends successfully to the UDG regime—although the UDGs in our sample show unusually low star formation rate surface densities given their H i content, this low star formation efficiency can be naturally explained by the diffuse structure of the UDGs. In fact, when cast in the PRFM framework, the relationship between midplane pressure and star formation in the UDG sample is in good agreement not only with the “normal” dwarf reference sample, but also with measurements from more massive galaxies. Our results suggest that despite their low star formation efficiencies, the H i -rich UDGs need not be forming stars in an exotic manner. We also find that the UDGs are likely H 2 poor compared even to the overall dwarf population. 

We investigate cosmological structure formation in fuzzy dark matter (FDM) with the attractive self-interaction (SI) with numerical simulations. Such a SI would arise if the FDM boson were an ultra-light axion, which has a strong CP symmetry-breaking scale (decay constant). Although weak, the attractive SI may be strong enough to counteract the quantum ‘pressure’ and alter structure formation. We find in our simulations that the SI can enhance small-scale structure formation, and soliton cores above a critical mass undergo a phase transition, transforming from dilute to dense solitons.

 

Abstract Stellar winds contain enough energy to easily disrupt the parent cloud surrounding a nascent star cluster, and for this reason they have long been considered candidates for regulating star formation. However, direct observations suggest most wind power is lost, and Lancaster et al. recently proposed that this is due to efficient mixing and cooling processes. Here we simulate star formation with wind feedback in turbulent, self-gravitating clouds, extending our previous work. Our simulations cover clouds with an initial surface density of 10 2 –10 4 M ⊙ pc −2 and show that star formation and residual gas dispersal are complete within two to eight initial cloud freefall times. The “efficiently cooled” model for stellar wind bubble evolution predicts that enough energy is lost for the bubbles to become momentum-driven; we find that this is satisfied in our simulations. We also find that wind energy losses from turbulent, radiative mixing layers dominate losses by “cloud leakage” over the timescales relevant for star formation. We show that the net star formation efficiency (SFE) in our simulations can be explained by theories that apply wind momentum to disperse cloud gas, allowing for highly inhomogeneous internal cloud structure. For very dense clouds, the SFE is similar to those observed in extreme star-forming environments. Finally, we find that, while self-pollution by wind material is insignificant in cloud conditions with moderate density (only ≲10 −4 of the stellar mass originated in winds), our simulations with conditions more typical of a super star cluster have star particles that form with as much as 1% of their mass in wind material. 

ABSTRACT Bose–Einstein condensate dark matter (BECDM, also known as fuzzy dark matter) is motivated by fundamental physics and has recently received significant attention as a serious alternative to the established cold dark matter (CDM) model. We perform cosmological simulations of BECDM gravitationally coupled to baryons and investigate structure formation at high redshifts (z ≳ 5) for a boson mass m = 2.5 × 10−22 eV, exploring the dynamical effects of its wavelike nature on the cosmic web and the formation of first galaxies. Our BECDM simulations are directly compared to CDM as well as to simulations where the dynamical quantum potential is ignored and only the initial suppression of the power spectrum is considered – a warm dark matter-like (‘WDM’) model often used as a proxy for BECDM. Our simulations confirm that ‘WDM’ is a good approximation to BECDM on large cosmological scales even in the presence of the baryonic feedback. Similarities also exist on small scales, with primordial star formation happening both in isolated haloes and continuously along cosmic filaments; the latter effect is not present in CDM. Global star formation and metal enrichment in these first galaxies are delayed in BECDM/‘WDM’ compared to the CDM case: in BECDM/‘WDM’ first stars form at z ∼ 13/13.5, while in CDM star formation starts at z ∼ 35. The signature of BECDM interference, not present in ‘WDM’, is seen in the evolved dark matter power spectrum: although the small-scale structure is initially suppressed, power on kpc scales is added at lower redshifts. Our simulations lay the groundwork for realistic simulations of galaxy formation in BECDM.