Outer regions of the merging system Arp 270

TL;DR

This study investigates the kinematics, metallicity, and star formation in the merging system Arp 270, revealing spatial separation of stars and gas, mild underabundance, and recent star formation in the intergalactic region.

Contribution

It provides detailed spectroscopic analysis of the peripheral regions of Arp 270, highlighting gas-star kinematic differences and the recent formation of intergalactic star-forming regions.

Findings

Stars and gas are spatially separated in NGC 3395.

Both galaxies are mildly underabundant with log(O/H) ≈ 8.4.

The intergalactic star-forming region formed recently from gas of NGC 3395.

Abstract

Arp 270 (NGC 3395 and NGC 3396) is the system of two actively star-forming late-type galaxies in contact, which already have experienced at least one close encounter in the past. We performed long-slit observations of peripheric regions of this merging system with the 6-m telescope of SAO RAS. Line-of-sight velocity distribution along the slits was obtained for gas and stellar population. We found that the stellar component of NGC 3395 differs by its velocity from the emission gas component in the extended region in the periphery, which evidences a spatial separation of stars and gas in the tidally disturbed galaxy. Gas abundances obtained by different methods demonstrate that both galaxies are mildly underabundant (log(O/H) $\approx 8.4$) without significant variations of metallicity along the slits. By comparing stellar and gaseous masses of galaxies we came to conclusion that the chemical evolution of gas is badly described by the closed box model. It allows us to admit that the significant part of interstellar gas was swept out of galaxies during the preceding encounter(s). A special attention was paid to the extended kpc-size island of star formation between the galaxies. We have not found neither noticeable kinematic decoupling of this region from the adjacent areas, nor any peculiarities of its emission spectra, which evidences that it was formed recently from the gas of NGC 3395 in the transition region between the colliding galaxies.