Structure, Kinematics, and Chemical Enrichment Patterns after Major Gas-Rich Disc-Disc Mergers

TL;DR

This study uses detailed simulations to explore how gas-rich disc galaxy mergers influence the resulting galaxy's structure, kinematics, and chemical composition, revealing consistent chemical signatures despite varied orbital parameters.

Contribution

It provides new insights into the structural, kinematic, and chemical outcomes of gas-rich galaxy mergers, highlighting the uniformity of chemical signatures across different merger scenarios.

Findings

Merger remnants often retain disc morphology due to high gas fractions.

Stars formed during mergers have distinct kinematic and chemical properties from those formed later.

Chemical properties of merger remnants are remarkably uniform despite different orbital parameters.

Abstract

We used an N-body smoothed particle hydrodynamics algorithm, with a detailed treatment of star formation, supernovae feedback, and chemical enrichment, to perform eight simulations of mergers between gas-rich disc galaxies. We vary the mass ratio of the progenitors, their rotation axes, and their orbital parameters and analyze the kinematic, structural, and chemical properties of the remnants. Six of these simulations result in the formation of a merger remnant with a disc morphology as a result of the large gas-fraction of the remnants. We show that stars formed during the merger (a sudden starburst occur in our simulation and last for 0.2-0.3 Gyr) and those formed after the merger have different kinematical and chemical properties. The first ones are located in thick disc or the halo. They are partially supported by velocity dispersion and have high [alpha/Fe] ratios even at metallicities as high as [Fe/H]=-0.5. The former ones -- the young component -- are located in a thin disc rotationally supported and have lower [alpha/Fe] ratios. The difference in the rotational support of both components results in the rotation of the thick disc lagging that of the thin disc by as much as a factor of two, as recently observed.We find that, while the kinematic and structural properties of the merger remnant depends strongly upon the orbital parameters of the mergers, there is a remarkable uniformity in the chemical properties of the mergers. This suggests that general conclusions about the chemical signature of gas-rich mergers can be drawn.