Global velocity field and bubbles in the blue compact dwarf galaxy Mrk 86

Abstract

We have studied the velocity field of the blue compact dwarf galaxy Mrk 86 (NGC 2537) using data provided by 14 long-slit optical spectra obtained in 10 different orientations and positions. This kinematical information is complemented with narrow-band ([O III]5007 Å and Hα) and broad-band (B, V, Gunn r and K) imaging. The analysis of the galaxy global velocity field suggests that the ionized gas could be distributed in a rotating inclined disc, with projected central angular velocity of Ω=34 km s^−1 kpc^−1. The comparison between the stellar, H I and modelled dark matter density profile indicates that the total mass within its optical radius is dominated by the stellar component. Peculiarities observed in its velocity field can be explained by irregularities in the ionized gas distribution or local motions induced by star formation. Kinematical evidences for two expanding bubbles, Mrk 86-B and Mrk 86-C, are given. They show expanding velocities of 34 and 17 km s^−1, Hα luminosities of 3×10^38 and 1.7×10^39 erg s^−1, and physical radii of 374 and 120 pc, respectively. The change in the [S II]/Hα, [N II]/Hα, [O II]/[O III] and [O III]/Hβ line ratios with the distance to the bubble precursor suggests a diminution in the ionization parameter and, in the case of Mrk 86-B, an enhancement of the shock-excited gas emission. The optical-near-infrared colours of the bubble precursors are characteristic of low-metallicity star-forming regions (∼0.2 Z_⊙) with burst strengths of about 1 per cent in mass.