Mapping the starburst in Blue Compact Dwarf Galaxies. PMAS Integral Field Spectroscopy of Mrk 1418

TL;DR

This study uses integral field spectroscopy to map and analyze the starburst regions, ionization mechanisms, and chemical abundances in the Blue Compact Dwarf Galaxy Mrk 1418, revealing a chemically homogeneous, high-metallicity star-forming environment.

Contribution

First detailed IFS mapping of Mrk 1418's starburst regions, revealing morphology, ionization, and chemical homogeneity in a high-metallicity BCD galaxy.

Findings

Star formation occurs in five knots around the nucleus.

Ionization is dominated by stellar photo-ionization, no other mechanisms detected.

The galaxy has a high, homogeneous metallicity of about 0.4 Z_solar.

Abstract

(Abridged) Aims: By means of optical Integral Field Spectroscopy (IFS) observations, we aim to disentangle and characterize the starburst component in the BCD Mrk 1418. In particular we propose to study the stellar and ionized gas morphology, to investigate the ionization mechanism(s) acting in the interstellar medium, to derive the physical parameters and abundances of the ionized gas. Methods: IFS observations of Mrk 1418 were carried out with PMAS at the 3.5 m telescope at CAHA. The central 16"x16" were mapped. From these data we built maps of the most prominent emission lines, namely [OII], H-beta, [OIII], H-alpha, [NII] and [SII] as well as of several continuum bands, plus maps of the main line ratios: [OIII]/H-beta, [NII]/H-alpha, [SII]/H-alpha, and H-alpha/H-beta, and derived the physical parameters and gaseous metal abundances of the different star-forming regions detected in the field of view. Results: Mrk 1418 shows a distorted morphology both in the continuum and in the ionized gas maps; the current star-formation episode is taking place in five knots, distributed around the nucleus of the galaxy. The interstellar medium surrounding these knots is photo-ionized by stars, with no clear evidence for other excitation mechanisms. The galaxy displays an inhomogeneous dust distribution, with the high H-alpha/H-beta ratio in the central areas indicating a large amount of dust. The oxygen abundances derived for the individual star-forming knots are very similar, suggesting that the ionized interstellar medium is chemically homogeneous in O/H over spatial scales of hundreds of parsecs. This abundance (Z~0.4 Z_solar from the empirical calibrations) places Mrk 1418 among the high metallicity BCD group.