We present spectra of a large sample of low-metallicity blue compact dwarf galaxies which exhibit broad components in their strong emission lines , mainly in H \beta , [ O iii ] \lambda 4959 , 5007 and H \alpha . Twenty-three spectra have been obtained with the MMT The MMT is operated by the MMT Observatory ( MMTO ) , a joint venture of the Smithsonian Institution and the University of Arizona . , 14 of which show broad emission . The remaining 21 spectra with broad emission have been selected from the Data Release 5 of the Sloan Digital Sky Survey . The most plausible origin of broad line emission is the evolution of massive stars and their interaction with the circumstellar and interstellar medium . The broad emission with the lowest H \alpha luminosities ( 10 ^ { 36 } –10 ^ { 39 } erg s ^ { -1 } ) is likely produced in circumstellar envelopes around hot Ofp/WN9 and/or LBV stars . The broad emission with the highest H \alpha luminosities ( 10 ^ { 40 } –10 ^ { 42 } erg s ^ { -1 } ) probably arises from type IIp or type IIn supernovae ( SNe ) . It can also come from active galactic nuclei ( AGN ) containing intermediate-mass black holes , although we find no strong evidence for hard non-thermal radiation in our sample galaxies . The oxygen abundance in the host galaxies 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 with 12 + log O/H \lesssim 7.99 . Spectroscopic monitoring of these type IIn SN / AGN candidates over a time scale of several years is necessary to distinguish between the two possibilities .