NGC 90: a hidden jelly-fish galaxy?

TL;DR

This study investigates the peculiar galaxy NGC 90, revealing tidal tails, a shallow oxygen abundance gradient, and a massive displaced HI cloud with ongoing star formation, suggesting complex interactions and gas dynamics.

Contribution

It provides detailed spectroscopic analysis of NGC 90, highlighting its unique gas distribution, star formation in the HI cloud, and the impact of galaxy interactions on its properties.

Findings

NGC 90 has tidal tails with young stars.

The galaxy exhibits a shallow oxygen abundance gradient.

A massive HI cloud shows signs of star formation and high velocity displacement.

Abstract

We study a peculiar galaxy NGC 90, a pair member of interacting system Arp 65 (NGC 90/93), using the long-slit spectral observations carried out at the Russian 6m telescope BTA and the available SDSS photometric data. This galaxy demonstrates two tidal tails containing young stellar population, being an extension of its `Grand Design' spiral arms. We obtained the distribution of velocity and oxygen abundance of emission gas (O/H) for two slit orientations. In the central part of the galaxy a significant role belongs to non-photoionization mechanism of line emission probably caused by shocks due to LINER-like activity of the nucleus. The O/H has a shallow abundance gradient, typical for interacting galaxies. The most intriguing peculiarity of the galaxy is the presence of the discovered earlier huge HI `cloud' containing about half of total mass of galaxy gas, which is strongly displaced outwards and has a velocity exceeding at about 340 km/s the central velocity of the main galaxy. We found traces of current star formation in the `cloud', even though the cloud is apparently not gravitationally bound with the galaxy. A possible nature of the `cloud' is discussed. We argue that it presents a flow of gas sweeping by ram pressure and elongated along a line of sight.