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We present a new model to explain the appearance of red/blueshifted broad low‐ionization emission lines, especially emission lines in the optical band, which is commonly considered as an indicator of radial motion of the line emitting gas in broad emission line regions (BLRs) of active galactic nuclei (AGN). We show that partly obscured disc‐like BLRs of dbp emitters (AGN with double‐peaked broad low‐ionization emission lines) can also successfully produce shifted standard Gaussian broad Balmer emission lines. Then, we select eight high‐quality objects (signal‐to‐noise ratio &gt; 40 at  r  band) with shifted standard Gaussian broad Hα (shifted velocity larger than  180 km s −1  ) from the Sloan Digital Sky Survey Data Release 4. All eight selected objects have visible stellar absorption features in their spectra, except SDSS J1007+1246, which allows us to estimate black hole (BH) masses through the  M –σ relation which has proven to be the most reliable method. We also calculate virial BH masses from the continuum luminosity and linewidth of broad Hα, assuming broad emission lines from ‘normal’ BLRs dominated by virialized motions. We find that the BH masses calculated from the  M –σ relation are systematically larger than virial BH masses for the selected objects, even after the correction of internal reddening effects in BLRs. The smaller virial BH masses than BH masses from the  M –σ relation for objects with shifted broad emission lines are coincident with what we expect from the partly obscured accretion disc model. Thus, we provide an optional better model to explain the appearance of shifted broad emission lines, especially for those objects with underestimated virial BH masses. Finally, we make predictions about the variation of shifted broad Hα with time for the two models: broad Hα from ‘normal’ radially moving clouds or broad Hα from dbp BLRs in a partly obscured accretion disc.

Partly obscured accretion disc model to explain shifted broad Balmer emission lines of active galactic nuclei