HUBBLE SPACE TELESCOPE SPECTROSCOPY OF FOUR LUMINOUS COMPACT BLUE GALAXIES AT INTERMEDIATE REDSHIFT1

We present a spectroscopic study of four blue (B V 0:6) compact (B 21:0 mag arcsec2) field galaxies with redshifts 0:095 z 0:438 and absolute magnitudesMB between 17.5 and 21.1. The spectra, taken with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope, show prominent emission lines whose spatial profiles reveal, at least in two cases, the existence of various star-forming regions and an underlying stellar population. The derived star formation rates from H luminosities in these star-forming regions range between 0.5 and 7 M yr1. These regions are typically 10 times more luminous than and approximately twice as large as the well-known giant H ii region 30 Doradus in the LMC.When compared with local starburst galaxies, the objects presented here turn out to be very similar to the brightest H ii galaxies in terms of the areal star formation rate and in the ratio between the galactic half-light diameter to the line-emitting region half-light diameter (DeA=D0)