The origin of the galaxy mass-metallicity relation and implications for galactic outflows

By K. Finlator, R. Dav'e. 2007

368 citations recorded by the source corpus.

Using cosmological hydrodynamic simulations that dynamically incorporate enriched galactic outflows together with analytical modelling, we study the origin of the stellar mass-gas-phase metallicity relation (MZR). We find that metallicities are driven by an equilibrium between the rate of enrichment owing to star formation and the rate of dilution owing to infall of unenriched gas. This equilibrium is in turn governed by the outflow strength. As such, the MZR provides valuable insights and strong constraints on galactic outflow properties across cosmic time. We compare three outflow models: no outflows, a 'constant-wind model that emulates the popular Dekel & Silk scenario, and a 'momentum-driven wind' model that best reproduces z ≥ 2 intergalactic medium metallicity data. Only the momentum-driven wind scaling simulation is able to reproduce the observed z ∼ 2 MZR's slope, amplitude, and scatter. In order to understand why, we construct a one-zone chemical evolution model guided by simulations. This model shows that the MZR in our outflow simulations can be understood in terms of three parameters: (i) the equilibrium metallicity Z g,eq = YS FR / ACC (where y = net yield), reflecting the enrichment balance between star formation rate S FR and gas accretion rate ACC ; (ii) the dilution time t d = M g /M SFR , representing the time-scale for a galaxy to return to Z g,eq after a metallicity-perturbing interaction; and (iii) the blowout mass M blowout , which is the galaxy stellar mass above which winds can escape its halo. Without outflows, galaxy metallicities exceed observations by approximately two to three times, although the slope of the MZR is roughly correct owing to greater star formation efficiencies in larger galaxies. When outflows with mass-loading factor η w are present, galaxies below M blowout obey Z g,eq ≈ y/(1 + η w ), while above M blowout , Z g,eq → y. Our constant-wind model has M blowout ∼ 10 10 M ⊙ , which yields a sharp upturn in the MZR above this scale and a flat MZR with large scatter below it, in strong disagreement with observations. Our momentum-driven wind model naturally reproduces the observed Z g ∞ M 0.3 * because Z g,eq ∞ η -1 w ∞ M 1/3 * when η w » 1 (i.e. at low masses). The flattening of the MZR at M* ≥ 10 10.5 M ⊙ observed by Tremonti et al. is reflective of the mass-scale where η w ∼ 1 rather than a characteristic outflow speed; in fact, the outflow speed plays little role in the MZR except through M blowout . The tight observed MZR scatter is ensured when t d ≤ dynamical time, which is only satisfied at all masses in our momentum-driven wind model. We also discuss secondary effects on the MZR, such as baryonic stripping from neighbouring galaxies' outflows.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/6bbd384f87549317ecec1dab26914c683f1a2c32

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THE CHARACTERISTIC STAR FORMATION HISTORIES OF GALAXIES AT REDSHIFTS z ∼ 2–7 (2012, background): “(11) 22 Hydrodynamical simulations suggest that under the assumption of momentum-driven winds, the instantaneous mass outflow rate ηinst ∝ v −1 c , where vc is the circular velocity, and hence ηinst ∝ M −1/3 ∗ (e.g., Finlator & Davé 2008; Davé et al. 2011).”
The EAGLE project: Simulating the evolution and assembly of galaxies and their environments (2014, methodology): “However, recent numerical experiments and analytic models provide some support for the general idea (e.g. Finlator & Davé 2008; Schaye et al. 2010; Booth & Schaye 2010; Davé et al. 2012; Haas et al. 2013a,b; Feldmann 2013; Dekel et al. 2013; Altay et al. 2013; Lilly et al. 2013; Sánchez Almeida…”
A fundamental relation between mass, SFR and metallicity in local and high redshift galaxies (2010, background): “On the one hand, infall of metal poor gas directly reduces the observed metallicity by diluting the metal-rich gas, as discussed, for example, by Finlator & Davé (2008) in the context of their wind scheme.”
JWST Census for the Mass–Metallicity Star Formation Relations at z = 4–10 with Self-consistent Flux Calibration and Proper Metallicity Calibrators (2023, methodology): “These measurements can be used in conjunction with cosmological simulations ( e.g., Finlator & Davé 2008; Ma et al. 2016; Torrey et al. 2019; Langan et al. 2020; Ucci et al. 2023 ) and chemical evolution models ( e.g., Davé et al. 2012; Lilly et al. 2013; Dayal & Ferrara 2018 ) to gain insights…”
Feedback and recycled wind accretion: assembling the z= 0 galaxy mass function (2009, methodology): “…of empirical successes, including the z = 6 galaxy luminosity function (Davé, Finlator, & Oppenheimer 2006), the galaxy mass-metallicity relation (Finlator & Davé 2008), observations of IGM metal enrichment over a wide range of redshifts (Oppenheimer & Davé 2006, 2009; Oppenheimer, Davé, &…”
Galaxy Evolution in Cosmological Simulations with Outflows II: Metallicities and Gas Fractions (2011, methodology): “Stated in terms of the above formalism, the effective mass loading factor in these models approach zero above that threshold mass (see Finlator & Davé 2008 and §2.2 of Paper I), so that at low masses η ≈ 2 while at high masses η ≈ 0, with a steep transition between these regimes across which the…”
Implementing molecular hydrogen in hydrodynamic simulations of galaxy formation (2012, methodology): “In order to account for the fact that observations of gas metallicity are determined for HII regions, the metallicities of the gas were scaled by the star formation probability, as in Davé et al. (2007) and Finlator & Davé (2008).”
The origin and evolution of the galaxy mass–metallicity relation (2015, background): “Such models have also been modified to work in cosmological contexts and describe the evolution of MZR (e.g. Finlator & Davé 2008; Davé et al. 2012; Lilly et al. 2013).”
THE SINS SURVEY OF z ∼ 2 GALAXY KINEMATICS: PROPERTIES OF THE GIANT STAR-FORMING CLUMPS (2010, background): “This “star formation feedback” is widely thought to be a key ingredient in the evolution of starforming galaxies (Dekel & Silk 1986; Kauffmann et al. 1993; Finlator & Davé 2008; Efstathiou 2000; Bouché et al. 2010; Dutton et al. 2010).”
The properties of satellite galaxies in simulations of galaxy formation (2009, methodology): “Similar, but different wind models have been used successfully to investigate the ejection of intergalactic metals (Oppenheimer & Davé 2006, 2008) and the galaxy mass-metallicity relation of massive galaxies (M∗ & 10 9M⊙; Finlator & Davé 2008).”
GAS REGULATION OF GALAXIES: THE EVOLUTION OF THE COSMIC SPECIFIC STAR FORMATION RATE, THE METALLICITY–MASS–STAR-FORMATION RATE RELATION, AND THE STELLAR CONTENT OF HALOS (2013, background): “…have included differing star-formation efficiencies within galaxies (e.g. Brooks et al 2007, Mouhcine et al 2008, Calura et al., 2009), supernova-driven winds (e.g. Larson 1974, T+04, Dalcanton, 2007, Finlator & Davé 2008), and variations in the initial mass function of stars (Köppen et al 2007).”
A fundamental relation between the metallicity, gas content, and stellar mass of local galaxies (2013, background): “…for the relation have focused on explanations involving the global behaviour of gas (i.e. Audouze & Tinsley 1976), which can serve both as a pristine infalling diluent (e.g. Finlator & Davé 2008; Davé et al. 2010) and as a metal-rich outflow (Spitoni et al. 2010; Peeples & Shankar 2011).”
THE MASS–METALLICITY RELATION WITH THE DIRECT METHOD ON STACKED SPECTRA OF SDSS GALAXIES (2012, methodology): “Within the context of the Finlator & Davé (2008) model, this means that the direct method MZR implies a longer timescale for galaxies to re-equilibrate than the Mannucci et al. (2010) and T04 MZRs.”
The formation and survival of discs in a ΛcDM universe (2008, background): “…abundances (e.g. Springel & Hernquist 2003; Brook et al. 2004; Okamoto et al. 2005; Oppenheimer & Davé 2006; Stinson et al. 2006; Governato et al. 2007; Dalla Vecchia & Schaye 2008; Dubois & Teyssier 2008; Finlator & Davé 2008; Scannapieco et al. 2008 (hereafter S08); among recent examples).”
Mass, metal, and energy feedback in cosmological simulations (2007, methodology): “However, Finlator & Davé (2008) showed that a model in which galaxies expel material at constant velocity (i.e. the “constant wind” model of OD06) does not reproduce the observed mass-metallicity relation, primarily because outflows do not in fact couple their energy efficiently to ambient gas.”
Physical Models of Galaxy Formation in a Cosmological Framework (2014, methodology): “Z = yṀ∗ Ṁinflow ≈ y 1 + η , (8) where this approximation is valid in the limit of no recycled (i.e. previously enriched) accretion into the ISM (Finlator & Davé 2008).”
A fundamental problem in our understanding of low-mass galaxy evolution (2012, background): “It also reproduces the present- c© 2012 RAS, MNRAS 000, 000–000 day SMF below the knee of the mass function, and several other important galaxy population properties like the massmetallicity relation at z = 2 (Finlator & Davé 2008).”
A BUDGET AND ACCOUNTING OF METALS AT z ∼ 0: RESULTS FROM THE COS-HALOS SURVEY (2013, background): “…highly efficient winds that remove large amounts of freshly produced metals are necessary to understand the ISM abundances of both local and high-redshift galaxies (e.g., Dalcanton 2007; Erb 2008; Finlator & Davé 2008; Arrigoni 2010; Peeples & Shankar 2011; Davé et al. 2011; Dayal et al. 2013).”