Arp 58 and Arp 68: two M 51- type systems

TL;DR

This study compares two M 51-type galaxy systems, Arp 58 and Arp 68, revealing differences in gas dynamics, star formation activity, and metallicity, influenced by their mass, gas content, and environment.

Contribution

It provides detailed spectroscopic analysis of two contrasting M 51-type systems, highlighting their gas kinematics, star formation, and metallicity distributions, and relates these to their evolutionary states.

Findings

Strong non-circular gas motions observed in both systems.

Arp 68 shows ongoing starburst activity, unlike Arp 58.

Metallicity in Arp 68 is lower than expected for its luminosity.

Abstract

We study two M 51-type systems Arp 68 and Arp 58, which strongly differ by their stellar masses, gas content and environment. Long-slit spectral observations obtained at the 6-m telescope BTA were used to trace the distributions of a line-of-sight (LOS) velocity and a gas-phase oxygen abundance along the spectral cuts. Two systems are compared by their observed properties. We found a very strong large-scale non-circular motion of gas in both systems and a kpc-size saw-edged velocity profile along the tidal spiral arm of Arp 68, probably caused by the gas outflow due to the stellar feedback. A deep decrease of LOS velocity is also found in the `hinge' region in Arp 58, where the inner spiral arm transforms into the tidal spiral arm, which was predicted earlier for M 51-type galaxies. Local sites of star formation and the satellites are compared with the evolutionary models at the colour-colour diagrams. Unlike the spiral galaxy Arp 58, the main galaxy in Arp 68 system is experiencing an ongoing burst of star formation. Gas-phase metallicity estimates show that Arp 58 has a higher metal abundance and reveals a shallow negative radial gradient of the gas-phase oxygen abundance. The emission gas in Arp 68 has noticeably lower metallicity than it is expected for a given luminosity of this galaxy, which may be connected with its space position in the local void.