ESO 089−G018 and ESO 089−G019: long-slit spectroscopy of emission-line galaxies

Abstract

We present the first spectroscopic observations for the galaxies ESO 089-G018 (hereafter G18, an Sb(?)-type galaxy seen nearly edge-on) and ES0089-G019 (hereafter G19, an SA(s): a peculiar galaxy), extracted from the sample of ring-shaped galaxies compiled in Faundez-Abans & de Oliveira-Abans. The main goal of this work is to investigate the spectral classification using the three line-ratio diagrams, called diagnostic diagrams, of Veilleux & Osterbrock. However, in order to separate the different types of galaxies [H II galaxies, Seyfert 2 galaxies and low-ionization nuclear emission-line region galaxies (LINERs)] we have to used empirical boundaries between them. Based on the observed spectra, we suggest G18 is a 'weak-[O I] LINER' or even a 'transition object' or LINER/H II. In the case of G19, we see Hβ in absorption and no [O III] lines, impeding the [O III]/Hβ ratio to be estimated. However, other lines ratios have been evaluated for the discussion. We classify the nature of G19 as ambiguous, because of the difficulty in determining its ionizing source (narrow-line active galactic nuclei or H II galaxies) in different diagnostic diagrams. The errors in the fluxes were mostly caused by uncertainties in the placement of the continuum level. We have estimated nuclear redshift of z = 0.034 (G18) and z = 0.039 (G19), corresponding to a heliocentric velocity of 10 246 and 11 734 km s -1 , respectively. Some other physical parameters have been derived whenever possible. All spectra were reduced and analysed in a homogeneous way with the standard IRAF procedures.