NGC 90: a hidden jellyfish galaxy?

Abstract

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 6-m 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 H i ‘cloud’ containing about half of total mass of galaxy gas, which is strongly displaced outwards and has a velocity exceeding at about 340 $\rm {km~s^{-1}}$ 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 being sweeped by ram pressure and elongated along a line of sight.