An imaging and spectroscopic study of the very metal-deficient blue compact dwarf galaxy Tol 1214-277

We present a spectrophotometric study based on VLT/FORS I observations of o ne of the most metal-deficient blue compact dwarf (BCD) galaxies known, Tol 1214-277 (Z similar to Z(.)/25). The data show that roughly half of the to tal luminosity of the BCD originates from a bright and compact starburst re gion located at the northeastern tip of a faint dwarf galaxy with cometary appearance. The starburst has ignited less than 4 Myr ago and its emission is powered by several thousand O7V stars and similar to 170 late-type nitro gen Wolf-Rayet stars located within a compact region with less than or simi lar to 500 pc in diameter. For the first time in a BCD, a relatively strong [Fe V] lambda 4227 emission line is seen which together with intense He II lambda 4686 emission indicates the presence of a very hard radiation field in Tol 1214-277. We argue that this extraordinarily hard radiation origina tes from both Wolf-Rayet stars and radiative shocks in the starburst region . The structural properties of the low surface brightness (LSB) component u nderlying the starburst have been investigated by means of surface photomet ry down to 28 B mag arcsec(-2). We find that, for a surface brightness leve l fainter than similar to 24.5 B mag arcsec(-2), an exponential fitting law provides an adequate approximation to its radial intensity distribution. T he broadband colors in the outskirts of the LSB component of Tol 1214-277 a re nearly constant and are consistent with an age below one Gyr. This concl usion is supported by the comparison of the observed spectral energy distri bution (SED) of the LSB host with theoretical SEDs.