GRAPE-SPH Chemodynamical Simulation of Elliptical Galaxies I: Evolution of Metallicity Gradients

We simulate the formation and chemodynamical evolution of 124 elliptical galaxies by using a GRAPE-SPH code that includes various physical processes 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 CDM-based scenario, galaxies form through the successive merging of sub-galaxies 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. 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. 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 gradient dlog Z/dlog r ~ -0.3 with dispersion of +- 0.2 and no correlation between gradient and galaxy mass are consistent with observations of Mg2 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 by either monolithic collapse or by major merger alone. Rather it requires a model in which both formation processes arise, such as the present CDM scheme.Comment: Accepted for publication in MNRAS. 21 pages, 14 figures, some color. mpeg simulations available at http://www.MPA-Garching.MPG.DE/~chiaki/movie.htm

Simulations of Cosmic Chemical Enrichment with Hypernova

We simulate cosmic chemical enrichment with a hydrodynamical model including supernova and hypernova feedback. We find that the majority of stars in present-day massive galaxies formed in much smaller galaxies at high redshifts, despite their late assembly times. The hypernova feedback drives galactic outflows efficiently in low mass galaxies, and these winds eject heavy elements into the intergalactic medium. The ejected baryon fraction is larger for less massive galaxies, correlates well with stellar metallicity. The observed mass-metallicity relation is well reproduced as a result of the mass-dependent galactic winds. We also predict the cosmic supernova and gamma-ray burst rate histories.Comment: Proceedings of the CRAL-Conference Series I "Chemodynamics: from first stars to local galaxies

GRAPE-SPH Chemodynamical Simulation of Elliptical Galaxies II: Scaling Relations and the Fundamental Plane

We simulate the formation and chemodynamical evolution of 128 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. We find that the star formation timescale controls when and where stars form in the contracting gas cloud, determines the effective radius at given mass, and is constrained by observation to be ten times longer than the local dynamical timescale. We succeed in reproducing the observed global scaling relations under our CDM-based scenario, e.g., the Faber-Jackson relation, the Kormendy relation, and the fundamental plane. An intrinsic scatter exists along the fundamental plane, and the origin of this scatter lies in differences in merging history. Galaxies that undergo major merger events tend to have larger effective radii and fainter surface brightnesses, which result in larger masses, smaller surface brightnesses, and larger mass-to-light ratios. We can also reproduce the observed colour-magnitude and mass-metallicity relations, although the scatter is larger than observed. The scatter arises because feedback is not very effective and star formation does not terminate completely in our simulations. ~25% of accreted baryons are blown away in the simulations, independent of the assumed star formation timescale and initial mass function. Most heavy elements end up locked into stars in the galaxy. The ejected metal fraction depends only on the star formation timescale, and is ~2% even to rapid star formation.Comment: Accepted for publication in MNRAS. 13 pages mpeg simulations available at http://www.MPA-Garching.MPG.DE/~chiaki/movie.htm

Galactic and Cosmic Chemical Evolution with Hypernovae

We provide new nucleosynthesis yields depending on metallicity and energy (i.e., (normal supernovae and hypernovae), and show the evolution of heavy element abundances from C to Zn in the solar neighborhood. We then show the chemodynamical simulation of the Milky Way Galaxy and discuss the G-dwarf problem. We finally show the cosmological simulation and discuss the galaxy formation and chemical enrichment.Comment: 6 pages, 3 figure. To appear in the Proceedings of the IAU Symposium 228 "From Li to U: Elemental Tracers of Early Cosmic Evolution", eds. V. Hill, P. Francois and F. Primas, Cambridge University Pres

Manganese spread in Ursa Minor as a proof of sub-classes of type Ia supernovae

Context. Recently, new sub-classes of Type Ia supernovae (SNe Ia) were discovered, including SNe Iax. The suggested progenitors of SNe Iax are relatively massive, possibly hybrid C+O+Ne white dwarfs, which can cause white dwarf winds at low metallicities. There is another class that can potentially occur at low or zero metallicities; sub-Chandrasekhar mass explosions in single and/or double degenerate systems of standard C+O white dwarfs. These explosions have different nucleosynthesis yields compared to the normal, Chandrasekhar mass explosions. Aims. We test these SN Ia channels using their characteristic chemical signatures. Methods. The two sub-classes of SNe Ia are expected to be rarer than normal SNe Ia and do not affect the chemical evolution in the solar neighbourhood; however, because of the shorter delay time and/or weaker metallicity dependence, they could influence the evolution of metalpoor systems. Therefore, we have included both in our stochastic chemical evolution model for the dwarf spheroidal galaxy Ursa Minor. Results. The model predicts a butterfly-shape spread in [Mn/Fe] in the interstellar medium at low metallicity and - at the same time - a decrease of [alpha/Fe] ratios at lower [Fe/H] than in the solar neighbourhood, both of which are consistent with the observed abundances in stars of Ursa Minor. Conclusions. The surprising agreement between our models and available observations provides a strong indication of the origins of these new sub-classes of SNe Ia. This outcome requires confirmation by future abundance measurements of manganese in stars of other satellite galaxies of ourMilkyWay. It will be vital for this project to measure not the most extreme metal-poor tail, as more commonly happens, but the opposite; the metal-rich end of dwarf spheroidals.Comment: 8 pages, 6 figures, accepted for publication in A&

Evolution of N/O ratios in galaxies from cosmological hydrodynamical simulations

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We study the redshift evolution of the gas-phase O/H and N/O abundances, both (i) for individual interstellar medium (ISM) regions within single spatially resolved galaxies and (ii) when dealing with average abundances in the whole ISM of many unresolved galaxies. We make use of a cosmological hydrodynamical simulation including detailed chemical enrichment, which properly takes into account the variety of different stellar nucleosynthetic sources of O and N in galaxies. We identify 33 galaxies in the simulation, lying within dark matter haloes with virial mass in the range 10 11 ≤ M DM ≤ 10 13 M ⊙ and reconstruct how they evolved with redshift. For the local and global measurements, the observed increasing trend of N/O at high O/H can be explained, respectively, (i) as the consequence of metallicity gradients that have settled in the galaxy ISM, where the innermost galactic regions have the highest O/H abundances and the highest N/O ratios, and (ii) as the consequence of an underlying average mass-metallicity relation that galaxies obey as they evolve across cosmic epochs, where - at any redshift - less massive galaxies have lower average O/H and N/O ratios than the more massive ones. We do not find a strong dependence on the environment. For both local and global relations, the predicted N/O-O/H relation is due to the mostly secondary origin of N in stars. We also predict that the O/H and N/O gradients in the galaxy ISM gradually flatten as functions of redshift, with the average N/O ratios being strictly coupled with the galaxy star formation history. Because N production strongly depends on O abundances, we obtain a universal relation for the N/O-O/H abundance diagram whether we consider average abundances of many unresolved galaxies put together or many abundance measurements within a single spatially resolved galaxy.Peer reviewedFinal Accepted Versio

The metallicity and elemental abundance maps of kinematically atypical galaxies for constraining minor merger and accretion histories

© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.Explaining the internal distribution and motions of stars and gas in galaxies is a key aspect in understanding their evolution. In previous work we identified five well-resolved galaxies with atypical kinematics from a cosmological simulation; two had kinematically distinct cores (KDCs), and three had counter-rotating gas and stars (CRGD). In this paper, we show that (i) the KDC galaxies have flattening of stellar [O/Fe] at large galactocentric radii due to the minor mergers that gave rise to the KDCs, and (ii) the CRGD galaxies have an abrupt transition in the gas metallicity maps, from high metallicity in the centre to very low metallicity further out. These galaxies are embedded in dark matter filaments where there is a ready supply of near-pristine gas to cause this effect. The non-linear increase in gas metallicity is also seen in the radial profiles, but when the metallicity gradients are measured, the difference is buried in the scatter of the relation. We also find that all five galaxies are fairly compact, with small effective radii given their stellar masses. This is because they have not experienced major mergers that kinematically heat the stars, and would have destroyed their unusual kinematics. In order to detect these signatures of minor mergers or accretion, the galaxy scaling relations or radial metallicity profiles are not enough, and it is necessary to obtain the two-dimensional maps with integral field spectroscopy observations.Peer reviewe

On the [α/Fe]-[Fe/H] relations in early-type galaxies

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We study how the predicted [α/Fe]-[Fe/H] relations in early-type galaxies vary as functions of their stellar masses, ages, and stellar velocity dispersions, by making use of cosmological chemodynamical simulations with feedback from active galactic nuclei. Our model includes a detailed treatment for the chemical enrichment from dying stars, core-collapse supernovae (both Type II and hypernovae) and Type Ia supernovae. At redshift z = 0, we create a catalogue of 526 galaxies, among which we determine 80 early-type galaxies. From the analysis of our simulations, we find [α/Fe]-[Fe/H] relations similar to the Galactic bulge. We also find that, in the oldest galaxies, Type Ia supernovae start to contribute at higher [Fe/H] than in the youngest ones. On the average, early-type galaxies with larger stellar masses (and, equivalently, higher stellar velocity dispersions) have higher [α/Fe] ratios, at fixed [Fe/H]. This is qualitatively consistent with the recent observations of Sybilska et al., but quantitatively there are mismatches, which might require stronger feedback, sub-classes of Type Ia Supernovae, or a variable initial mass function to address.Peer reviewedFinal Published versio

Zoom-in cosmological hydrodynamical simulation of a star-forming barred, spiral galaxy at redshift z=2

Accepted for publication in MNRASWe present gas and stellar kinematics of a high-resolution zoom-in cosmological chemodynamical simulation, which fortuitously captures the formation and evolution of a star-forming barred spiral galaxy, from redshift $z\sim3$ to $z\sim2$ at the peak of the cosmic star formation rate. The galaxy disc grows by accreting gas and substructures from the environment. The spiral pattern becomes fully organised when the gas settles from a thick (with vertical dispersion $\sigma_{v} >$ 50 km/s) to a thin ($\sigma_{v} \sim 25$ km/s) disc component in less than 1 Gyr. Our simulated disc galaxy also has a central X-shaped bar, the seed of which formed by the assembly of dense gas-rich clumps by $z \sim 3$. The star formation activity in the galaxy mainly happens in the bulge and in several clumps along the spiral arms at all redshifts, with the clumps increasing in number and size as the simulation approaches $z=2$. We find that stellar populations with decreasing age are concentrated towards lower galactic latitudes, being more supported by rotation, and having also lower velocity dispersion; furthermore, the stellar populations on the thin disc are the youngest and have the highest average metallicities. The pattern of the spiral arms rotates like a solid body with a constant angular velocity as a function of radius, which is much lower than the angular velocity of the stars and gas on the thin disc; moreover, the angular velocity of the spiral arms steadily increases as function of time, always keeping its radial profile constant. The origin of our spiral arms is also discussed.Peer reviewe

The role of mass loss in chemodynamical evolution of galaxies

© The Author(s), 2022. Published by Cambridge University Press on behalf of International Astronomical Union. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.Thanks to the long-term collaborations between nuclear and astrophysics, we have good understanding on the origin of elements in the universe, except for the elements around Ti and some neutron-capture elements. From the comparison between observations of nearby stars and Galactic chemical evolution models, a rapid neutron-capture process associated with core-collapse supernovae is required. The production of C, N, F and some minor isotopes depends on the rotation of massive stars, and the observations of distant galaxies with ALMA indicate rapid cosmic enrichment. It might be hard to find very metal-poor or Population III (and dust-free) galaxies at very high redshifts even with JWST.Peer reviewe