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The Sloan Digital Sky Survey (SDSS) discovered a few unusual quasars with acharacteristic break in the continuum around 3000 A that neither shows thetypical structure of broad absorption line (BAL) troughs nor is explained bytypical intrinsic dust reddening. We used the method of Kohonen self-organisingmaps for a systematical search for quasars with such properties in the SDSSspectra archive. We constructed a sample of 23 quasars classified as 3000 Abreak quasars and two comparison samples of quasars with similar properties, tosome extent, but also showing typical BAL features. We computedensemble-averaged broad-band SEDs based on archival data from SDSS, GALEX,2MASS, UKIDSS, and WISE. The SEDs were corrected for intrinsic dust absorptionby the comparison with the average SED of normal quasars. The de-reddenedarithmetic median composite SED of the 3000 A break quasars is found to beindistinguishable from that of the unusual BAL quasars. We conclude that 3000 Abreak quasars are most likely extreme versions of BAL quasars. Assuming thatthe intrinsic SED of the continuum source is represented by the quasarcomposite SED, the 3000 A break quasars tend to be intrinsically more luminousthan ordinary quasars. (Abstract modified to match the arXiv format.)

Broad-band spectral energy distribution of 3000 Angstroem break quasars from the Sloan Digital Sky Survey