Mapping the starburst in blue compact dwarf galaxies - PMAS integral field spectroscopy of Mrk?1418

摘要

Aims. By means of optical integral field spectroscopyobservations, we aim to differentiate and characterize the starburstcomponent in the blue compact dwarf (BCD) galaxy Mrk1418. Inparticular we propose to study the stellar and ionized gas morphology,to investigate the ionization mechanism(s) acting in the interstellarmedium, and to derive the physical parameters and abundances of theionized gas. Methods. Integral field spectroscopy observations ofMrk1418 were carried out with the Potsdam multi-aperturespectrophotometer (PMAS) at the 3.5m telescope at Calar AltoObservatory. The central (1.141.14kpc2 at the distance of Mrk1418) were mapped with a spatial sampling of;we took data in the 3590-6996? spectral range, with a lineardispersion of 3.2?perpixel. The seeing wasabout.From these data we built maps of the most prominent emission lines, namely[O II], H,[O III], H,[N II], and [S II], as well as of several continuum bands, plus maps of the main line ratios: [O III]/H,[N II]/H,[S II]/H,and H/H,and derived the physical parameters and gaseous metal abundances of thedifferent star-forming regions detected in the field of view. Results. Mrk1418 shows a distorted morphology both in thecontinuum and in the ionized gas maps; the current star- formationepisode is taking place in five knots, distributed around the nucleusof the galaxy. The interstellar medium surrounding these knots isphoto-ionized by stars, with no clear evidence for other excitationmechanisms. The galaxy displays an inhomogeneous dust distribution,with the high H/Hratioin the central areas indicating a large amount of dust. The oxygenabundances derived for the individual star-forming knots are verysimilar, suggesting that the ionized interstellar medium is chemicallyhomogeneous in O/H over spatial scales of hundreds of parsecs. Thisabundance (from the empirical calibrations) places Mrk1418 among the high metallicity BCDgroup. Conclusions. These findings show the advantages of IFS wheninvestigating the properties of such complex objects as BCDs, with anasymmetric star-forming component. Only a bidimensional mapping oftheir central regions allows approaching such questions as the starformation processes in BCDs, the star-forming history of the individualstarburst knots, or the abundance gradients. Key words: galaxies: dwarf - galaxies: starburst - galaxies: stellar content - galaxies: individual: Mrk 1418 - ISM: HII regions