The disk galaxy simulated using our chemodynamic galaxy formation code, GCD+, is shown to have a thickdisk component. This is evidenced by the velocity dispersion versus age relation for solar neighborhood stars, which clearly shows an abrupt increase in velocity dispersion at a look-back time of approximately 8 Gyr, and is in excellent agreement with observation. These thick-disk stars are formed from gas that is accreted to the galaxy during a chaotic period of hierarchical clustering at high redshift. This formation scenario is shown to be consistent with observations of both the Milky Way and extragalactic thick disks.

We have developed a new galactic chemodynamical evolution code, called gcd+, for studies of galaxy formation and evolution. This code is based on our original three‐dimensional tree N‐body/smoothed particle hydrodynamics code which includes self‐gravity, hydrodynamics, radiative cooling, star formation, supernova feedback and metal enrichment. gcd+ includes a new Type II (SNe II) and Ia (SNe Ia) supernovae model, taking into account the lifetime of progenitor stars and chemical enrichment from intermediate‐mass stars. We apply gcd+ to simulations of elliptical galaxy formation, and examine the colour–magnitude relation (CMR), the Kormendy relation, and the [Mg/Fe]–magnitude relation of simulation end‐products. gcd+ is a useful and unique tool which enables us to compare simulation results with the observational data directly and quantitatively. Our simulation confirm the results of Kawata, who uses a simpler chemodynamical evolution code. We newly find that radiative cooling becomes more efficient and thus the gas infall rate increases, with decreasing mass of galaxies, which contributes to the slope of the CMR. In addition, the sophisticated treatments of both SNe II and SNe Ia in gcd+ show that feedback from SNe Ia plays a crucial role in the evolution of elliptical galaxies. We conclude that the feedback effect of SNe Ia should not be ignored in studying the evolution of elliptical galaxies.

We use a cosmological chemodynamical simulation to study how the group environment impacts the star formation properties of disk galaxies. The simulated group has a total mass of M~8x10^12 Msun and a total X-ray luminosity of L_X~10^41 erg s^-1. Our simulation suggests that ram pressure is not sufficient in this group to remove the cold disk gas from a V_rot~150 km s^-1 galaxy. However, the majority of the hot gas in the galaxy is stripped over a timescale of approximately 1 Gyr. Since the cooling of the hot gas component provides a source for new cold gas, the stripping of the hot component effectively cuts off the supply of cold gas. This in turn leads to a quenching of star formation. The galaxy maintains the disk component after the cold gas is consumed, which may lead to a galaxy similar to an S0. Our self-consistent simulation suggests that this strangulation mechanism works even in low mass groups, providing an explanation for the lower star formation rates in group galaxies relative to galaxies in the field.Comment: 5 pages, 4 figures, ApJL in pres

Aims. We examine radial and vertical metallicity gradients using a suite of disk galaxy hydrodynamical simulations, supplemented with two classic chemical evolution approaches. We determine the rate of change of gradient slope and reconcile the differences existing between extant models and observations within the canonical "inside-out" disk growth paradigm. Methods. A suite of 25 cosmological disks is used to examine the evolution of metallicity gradients; this consists of 19 galaxies selected from the RaDES (Ramses Disk Environment Study) sample, realised with the adaptive mesh refinement code ramses, including eight drawn from the "field" and six from "loose group" environments. Four disks are selected from the MUGS (McMaster Unbiased Galaxy Simulations) sample, generated with the smoothed particle hydrodynamics (SPH) code gasoline. Two chemical evolution models of inside-out disk growth were employed to contrast the temporal evolution of their radial gradients with those of the simulations. Results. We first show that generically flatter gradients are observed at redshift zero when comparing older stars with those forming today, consistent with expectations of kinematically hot simulations, but counter to that observed in the Milky Way. The vertical abundance gradients at ∼1−3 disk scalelengths are comparable to those observed in the thick disk of the Milky Way, but significantly shallower than those seen in the thin disk. Most importantly, we find that systematic differences exist between the predicted evolution of radial abundance gradients in the RaDES and chemical evolution models, compared with the MUGS sample; specifically, the MUGS simulations are systematically steeper at high-redshift, and present much more rapid evolution in their gradients. Conclusions. We find that the majority of the models predict radial gradients today which are consistent with those observed in late-type disks, but they evolve to this self-similarity in different fashions, despite each adhering to classical "inside-out" growth. We find that radial dependence of the efficiency with which stars form as a function of time drives the differences seen in the gradients; systematic differences in the sub-grid physics between the various codes are responsible for setting these gradients. Recent, albeit limited, data at redshift z ∼ 1.5 are consistent with the steeper gradients seen in our SPH sample, suggesting a modest revision of the classical chemical evolution models may be required.