David I. Méndez

Imaging and Spectrophotometry of Markarian 1094: Implications for the Recent Star Formation

Narrowband Hα imaging and intermediate- and high-resolution optical spectrophotometry have been obtained for the blue compact dwarf Wolf-Rayet galaxy Mrk 1094. The galaxy presents a bar-shaped structure and is currently undergoing a strong star formation burst distributed in several spatially separated knots. Analysis of the properties of the individual knots indicates that the brightest ones have sizes and luminosities similar to those of giant H II regions in Local Group galaxies. The Hα equivalent width map of Mrk 1094 indicates that star formation has not been strictly coeval all along the bar. We discuss the different processes that could explain these observational facts and conclude that interaction with a companion H I cloud could be the reason for the present enhanced star-forming process and the bar-shaped distribution of the different star-forming knots.

POX 4 and Tol 35: Two Peculiar Wolf-Rayet Dwarf Galaxies

We present results of narrowband (Hα and adjacent continuum) and broadband (U, B, and V) optical CCD imaging together with high-resolution Hα spectroscopy of the blue compact Wolf-Rayet dwarf galaxies POX 4 and Tol 35. POX 4 has a fainter, irregular, and diffuse companion located 205 (4.7 kpc) along the minor axis of the galaxy, which is visible also in the Hα emission. The difference in recession velocity between the galaxy and the companion is about 130 km s-1. The observational results lead us to propose that POX 4 could be interpreted as a low-mass ring galaxy, produced by a head-on intrusion of the fainter companion. Regarding the other object, a spectrum taken along the major axis of Tol 35 shows the coexistence of systems of motion with a velocity difference of about 50 km s-1. Moreover, the deep continuum-subtracted Hα image of the galaxy shows very faint features that resemble the beginning of crossed tidal tails or gaseous filaments powered by the mechanical action of the young stellar population. In this sense, Tol 35 could be interpreted either as an object in an intermediate-stage merging process between two gas-rich dwarf galaxies or as an object suffering the effect of a galactic wind.

A multi-frequency study of the Wolf-Rayet blue compact dwarf galaxy He2-10

We present preliminary results on multi-wavelength observations of the Wolf-Rayet Blue Compact Dwarf Galaxy He2–10. These observations include Hα and continuum imaging, high-resolution Hα spectroscopy, high-resolution radio-continuum mapping at 6.3 and 3.5 cm and X-ray mapping. The deep Hα image reveals that the galaxy consists of a complex system of different star-forming knots surrounded by kpc-scale bubble-like and filamentary structures. The most interesting structure is a bipolar superbubble centered on the most intense star-formation knot. High-resolution spectroscopy of this structure indicates that it is expanding with a velocity in the range 75–250 km s −1 . This kind of outflows is likely to be produced by the mechanical action of stellar winds and supernovae explosions in the intense starbursts that the galaxy hosts. This scenario is consistent with the finding of a very steep radio spectral index in the extended radio continuum emission (α = −0.59) that confirms the presence of a large number of supernova remnants in the galaxy.