grape-sph chemodynamical simulation of elliptical galaxies — I. Evolution of metallicity gradients

By C. Kobayashi. 2003

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We simulate the formation and chemodynamical evolution of 124 elliptical galaxies using a GRAPE-SPH code that includes various physical processes that are associated with the formation of stellar systems: radiative cooling, star formation, feedback from Type II and Ia supernovae and stellar winds, and chemical enrichment. In our cold dark matter (CDM)-based scenario, galaxies form through the successive merging of subgalaxies with various masses. Their merging histories vary between a major merger at one extreme and a monolithic collapse of a slow-rotating gas cloud at the other extreme. We examine the physical conditions during 151 merging events that occur in our simulation. The basic processes driving the evolution of the metallicity gradients are as follows: (i) destruction by mergers to an extent dependent on the progenitor mass ratio; (ii) regeneration when strong central star formation is induced at a rate dependent on the gas mass of the secondary; and (iii) slow evolution as star formation is induced in the outer regions through late gas accretion. We succeed in reproducing the observed variety of the radial metallicity gradients. The average metallicity gradient Δlog Z/Δlog r ≃ -0.3 with dispersion of ± 0.2 and no correlation between gradient and galaxy mass are consistent with observations of Mg 2 gradients. The variety of the gradients stems from the difference in the merging histories. Galaxies that form monolithically have steeper gradients, while galaxies that undergo major mergers have shallower gradients. Thus merging histories can, in principle, be inferred from the observed metallicity gradients of present-day galaxies. The observed variation in the metallicity gradients cannot be explained either by monolithic collapse or by major merger alone. Rather it requires a model in which both formation processes arise, such as the present CDM scheme.

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Citations in the corpus

Mass, metal, and energy feedback in cosmological simulations (2007, background): “Kobayashi (2004) injects energy from galactic superwinds and supernovae thermally into a number of surrounding gas particles in a Smoothed Particle Hydrodynamic (SPH) simulation, and find that hypernovae with 10× the typical supernova energy are needed to enrich the IGM to observed levels while…”
How do minor mergers promote inside-out growth of ellipticals, transforming the size, density profile and dark matter fraction? (2012, background): “Steeper gradients at large radii then might imply a formation history dominated by minor mergers (White 1978; Kobayashi 2004, see however Pipino et al. 2010 for an alternative view).”
The SAURON project – XVII. Stellar population analysis of the absorption line strength maps of 48 early-type galaxies (2010, background): “The metallicity gradients are predicted to be strongly correlated with the efficiency of the dissipative process, and to only weakly depend on the remnant mass (Kobayashi 2004; Hopkins et al. 2009a, b).”
Metallicity and Nuclear Star Formation in Nearby Galaxy Pairs: Evidence for Tidally Induced Gas Flows (2005, background): “Large-scale gas flows combined with central bursts of star formation may be important for transforming merging galaxies into elliptical galaxies (e.g., Kauffmann et al. 1993; Kobayashi 2004; Springel et al. 2005; Nagashima et al. 2005).”
Simulations of Cosmic Chemical Enrichment (2006, background): “…not only of isolated systems (e.g. Mihos & Hernquist 1989; Katz 1992; Steinmetz & Müller 1994; Kawata & Gibson 2003; Nakasato & Nomoto 2003; Kobayashi 2004, hereafter K04) but also for cosmological simulations of individual galaxies (e.g. Navarro & White 1994) or of the galaxy population…”
De re metallica: the cosmic chemical evolution of galaxies (2018, background): “1 are obtained by Vincenzo et al. (in prep.) for stars of solar metallicity, with the IMF from Kroupa et al. (1993), stellar lifetimes from Kobayashi (2004), stellar yields from Nomoto et al. (2013), SNe Ia yields from Iwamoto et al. (1999), and a t−1 delay-time distribution for the type Ia SNe…”
Chemical enrichment of galaxy clusters from hydrodynamical simulations (2007, methodology): “…we have focused our analysis on the low-redshift enrichment of the ICM, a number of other studies can be foreseen, from the enrichment of the IGM at high redshift, z 2, to the metal abundances in both elliptical and disc galaxies (e.g. Kawata & Gibson 2003; Kobayashi 2004; Scannapieco et al. 2006).”
Chemical enrichment in cosmological, smoothed particle hydrodynamics simulations (2009, background): “2001; Kawata 2001; Lia et al. 2002; Kawata & Gibson 2003; Valdarnini 2003; Kobayashi 2004; Sommer-Larsen et al. 2005; Tornatore et al. 2007; Oppenheimer & Davé 2008), ranging from recipes that distinguish only between SN type Ia and SN type II elements to models that follow large numbers of…”
Chemodynamical evolution of the Milky Way disk - I. The solar vicinity (2012, background): “…of chemical evolution have been performed by a number groups (Raiteri et al., 1996; Mosconi et al., 2001; Lia et al., 2002; Kawata and Gibson, 2003; Kobayashi, 2004; Scannapieco et al., 2005; Martı́nez-Serrano et al., 2008; Oppenheimer and Davé, 2008; Wiersma et al., 2009; Few et al., 2012).”
The Aquila comparison project: the effects of feedback and numerical methods on simulations of galaxy formation (2011, background): “The details are described in Kobayashi (2004), Kobayashi et al. (2007) and Kobayashi & Nakasato (2011).”
The CALIFA survey across the Hubble sequence: Spatially resolved stellar population properties in galaxies (2015, background): “Shallow metallicity gradients are expected if elliptical galaxies result from major mergers (e.g. Kobayashi 2004), but a minor merger picture for the formation of ellipticals can successfully explain the strong size evolution of massive galaxies (Oser et al. 2012).”
The transition from population III to population II-I star formation (2010, methodology): “This is consistent with any simulation including metal enrichment (Raiteri et al. 1996; Gnedin 1998; Mosconiet al. 2001; Lia et al. 2002a,b; Kawata & Gibson 2003; Kobayashi 2004; Ricotti & Ostriker 2004; Scannapieco et al. 2005; Tornatoreet al. 2007; Oppenheimer et al. 2009).”
Cosmological simulations of the formation of the stellar haloes around disc galaxies (2011, methodology): “In the right 9 But note that hydrodynamic re-simulations have been used to study the radial distribution of metallicity in early-type galaxies (e.g., Kobayashi 2004, 2005; Gibson et al. 2007) and significant gradients were shown to be common in these systems as well. panel of Fig.”
METALLICITY-DEPENDENT QUENCHING OF STAR FORMATION AT HIGH REDSHIFT IN SMALL GALAXIES (2011, background): “…made so far to implement stellar feedback in simulations and semi-analytic models (SAM) are not really satisfactory (Springel & Hernquist 2003; Kobayashi 2004; Cen & Ostriker 2006; Oppenheimer & Davé 2006; Governato et al. 2007), because they operate on scales too small to be resolved, and…”
A model for cosmological simulations of galaxy formation physics: multi-epoch validation (2013, background): “…Katz et al. 1996; Wiersma et al. 2009a), and chemical enrichment (e.g., Steinmetz & Mueller 1994; Mosconi et al. 2001; Lia et al. 2002; Springel & Hernquist 2003a; Kobayashi 2004; Scannapieco et al. 2005; Tornatore et al. 2007; Oppenheimer & Davé 2008; Wiersma et al. 2009b; Few et al. 2012).”
Effects of feedback on the morphology of galaxy discs (2005, unknown): “On the other hand, some simulations of elliptical galaxy formation, have used large values ofc∗ = 0.5 ∼ 1 (e.g. Kawata & Gibson 2004; Kobayashi 2004), often with strong feedback, in order to reproduce the observed sizes and/or colours of elliptical galaxies.”
CHEMODYNAMICAL SIMULATIONS OF THE MILKY WAY GALAXY (2008, methodology): “We simulate the chemodynamical evolution of the Milky Way Galaxy with our GRAPESPH code (Kobayashi 2004), the details of which are summarized as follows. i) The Smoothed Particle Hydrodynamics (SPH) method is adopted, and the gravity is calculated by direct summation using the special purpose…”
DISSIPATION AND EXTRA LIGHT IN GALACTIC NUCLEI. IV. EVOLUTION IN THE SCALING RELATIONS OF SPHEROIDS (2008, result): “…(perhaps forming early in a rapid series of multiple, highly dissipational mergers, rather than a single disk-disk merger at late times), which might, in principle, “smear our” or bias some of these comparisons or systematically alter some predictions (see e.g. Kobayashi 2004; Naab et al. 2007).”
Spatially resolved spectroscopy of early-type galaxies over a range in mass (2007, background): “…processes tend to create stronger gradients, mergers between galaxies destroy these gradients (e.g., Mihos & Hernquist 1994; Kobayashi 2004) The mean metallicity gradients for non-merger and merger galaxies derived by Kobayashi (2004) are ∆[Z/H]/∆ log r ∼ −0.30 and −0.22, respectively.”
Feedback in simulations of disc-galaxy major mergers (2005, background): “These works use a wide range of star-formation efficiencies that are both higher (Katz 1992; Navarro & White 1993; Kobayashi 2004; Governato et al. 2004; Kawata & Gibson 2005) and lower (MH96; S00; Sommer-Larsen, Götz & Portinari 2003; Springel & Hernquist 2003) than ours.”