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We present spectra of a large sample of low-metallicity blue compact dwarfgalaxies which exhibit broad components in their strong emission lines, mainlyin Hbeta, [O III]4959, 5007 and Halpha. Twenty-three spectra have been obtainedwith the MMT, 14 of which show broad emission. The remaining 21 spectra withbroad emission have been selected from the Data Release 5 of the Sloan DigitalSky Survey. The most plausible origin of broad line emission is the evolutionof massive stars and their interaction with the circumstellar and interstellarmedium. The broad emission with the lowest H$\alpha$ luminosities (10^36 -10^39 erg/s) is likely produced in circumstellar envelopes around hot Ofp/WN9and/or LBV stars. The broad emission with the highest Halpha luminosities(10^40 - 10^42 erg/s) probably arises from type IIp or type IIn supernovae(SNe). It can also come from active galactic nuclei (AGN) containingintermediate-mass black holes, although we find no strong evidence for hardnon-thermal radiation in our sample galaxies. The oxygen abundance in the hostgalaxies with SN candidates is low and varies in the range 12 + log O/H = 7.36- 8.31. However, type IIn SN / AGN candidates are found only in galaxies with12 + log O/H < 7.99. Spectroscopic monitoring of these type IIn SN / AGNcandidates over a time scale of several years is necessary to distinguishbetween the two possibilities.

Broad Line Emission in Low-Metallicity Blue Compact Dwarf Galaxies: Evidence for Stellar Wind, Supernova and Possible AGN Activity