First Results from SMAUG: The Need for Preventative Stellar Feedback and Improved Baryon Cycling in Semianalytic Models of Galaxy Formation

Abstract

Semianalytic models (SAMs) are a promising means of tracking the physical processes associated with galaxy formation, but many of their approximations have not been rigorously tested. As part of the Simulating Multiscale Astrophysics to Understand Galaxies project, we compare predictions from the FIRE-2 hydrodynamical “zoom-in” simulations to those from the Santa Cruz SAM run on the same halo merger trees, with an emphasis on the global mass flow cycle. Our study includes 13 halos spanning low-mass dwarfs (M vir ∼ 1010 M ⊙ at z = 0), intermediate-mass dwarfs (M vir ∼ 1011 M ⊙), and Milky Way–mass galaxies (M vir ∼ 1012 M ⊙). The SAM and FIRE-2 predictions agree relatively well with each other in terms of stellar and interstellar medium mass but differ dramatically on circumgalactic medium mass (the SAM is lower than FIRE-2 by ∼3 orders of magnitude for dwarfs). Strikingly, the SAM predicts higher gas accretion rates for dwarfs compared to FIRE-2 by factors of ∼10–100, and this is compensated for with higher mass outflow rates in the SAM. We argue that the most severe model discrepancies are caused by the lack of preventative stellar feedback and the assumptions for halo gas cooling and recycling in the SAM. As a first step toward resolving these model tensions, we present a simple yet promising new preventative stellar feedback model in which the energy carried by supernova-driven winds is allowed to heat some fraction of gas outside of halos to at least the virial temperature such that accretion is suppressed.

Cosmological Simulations of Quasar Fueling to Subparsec Scales Using Lagrangian Hyper-refinement

“…This work has been developed with the support of the Simulating Multiscale Astrophysics to Understand Galaxies (SMAUG) consortium, 13 which attempts to reduce the uncertainties associated with subgrid parameterizations of key baryonic processes in galaxy formation in order to improve the accuracy of fundamental cosmological measurements. Other work in SMAUG has centered on star formation and stellar feedback (Li et al 2010(Li et al , 2020Kim et al 2020;Motwani et al 2020), the physics of the CGM (Fielding et al 2020), and the connection between semi-analytic models and cosmological hydrodynamic simulations (Pandya et al 2020). Our work complements these by providing a key step toward developing better subgrid models for black hole accretion in galaxy formation, which play a key role in the evolution of massive galaxies and large-scale structure.…”

“…The Feedback In Realistic Environments (FIRE) project 12 (Hopkins et al 2014a(Hopkins et al , 2018a implements stellar feedback on the scale of star-forming regions, injecting energy, momentum, mass, and metals from supernovae (SNe), stellar winds, and radiation directly based on the predictions of stellar population synthesis models. This yields a realistic ISM with multiphase structure and self-consistent generation of galactic winds (Muratov et al 2015;Anglés-Alcázar et al 2017b;Pandya et al 2021) while reproducing a variety of galaxy properties (e.g., Ma et al 2016Ma et al , 2017bWetzel et al 2016;Feldmann et al 2017;Sparre et al 2017;Garrison-Kimmel et al 2018;Cochrane et al 2019;Liang et al 2019) and circumgalactic medium (CGM) observables (e.g., Faucher-Giguère et al 2015, 2016Hafen et al 2017). The increased resolution and detailed stellar feedback have important implications for black hole scaling relations, AGN demographics, and galaxy quenching: stellar feedback can significantly suppress early black hole growth by efficiently evacuating gas from galactic nuclei (Anglés-Alcázar et al 2017c).…”

Characterizing mass, momentum, energy, and metal outflow rates of multiphase galactic winds in the FIRE-2 cosmological simulations

“…We see that even for the low-redshift MW halos, the actual halo mass loading is comparable to, in fact even slightly larger than, the ISM mass loading defined using particles with enough energy to make it to 2𝑅 vir . If we had included slower moving, likely cold and turbulent, ISM outflows -which never had a chance of getting to 2𝑅 vir anyway -then this ratio would be closer to 0.3 − 0.4 (Figure 12 of Pandya et al 2020). While we do not know whether the identity of the gas leaving the virial shell is the same as the gas that was previously ejected from the ISM (e.g., much of the ISM outflows could have stalled in the CGM while still pushing ambient halo gas outwards), our finding that 𝜂 halo /𝜂 ISM ∼ 1 in the low-redshift MW halos combined with their relatively large Bernoulli velocities of hot outflows in Figure 13 suggests that outflows can have substantial effects in MW halos (see also our supplementary movies, e.g., Figure 1).…”

“…As our work builds on the analysis of FIRE-2 presented in Pandya et al (2020), here we use the same halo catalogs and merger trees generated using the Rockstar and consistent-trees codes (Behroozi et al 2013a,b). For halo masses and radii, we adopt the Bryan & Norman (1998) virial overdensity definition.…”

“…Winds may also fuel a significant fraction of late-time star formation in more massive halos by recycling back into the interstellar medium (ISM; e.g., Oppenheimer et al 2010;Henriques et al 2013;White et al 2015;Anglés-Alcázar et al 2017a). In lower mass halos, SN-driven winds may more easily escape and heat the CGM/IGM, causing preventative feedback effects by suppressing gas accretion in the first place (e.g., Davé et al 2012;Lu et al 2015;Pandya et al 2020) and decreasing the metal and dust content of dwarfs (e.g., Davé et al 2011;Feldmann 2015).…”