Anomalous Narrow-Line Quasars in the Sloan Digital Sky Survey
(5 votes over all institutions)
We describe a new class of Type I quasars with narrow H\beta\ broader than 1200 km/s, above the velocity believed possible for gas in the quasar narrow-line region. This class appears to include two groups of objects, one with [O III]\lambda 4959,5007 also broadened and another with [O III]\lambda 4959,5007 suppressed but not broadened. These two groups of “anomalous narrow-line quasars” (ANLs) comprise at least 11% and most likely approximately one quarter of the SDSS Type I quasar population at 0.2 < z < 0.8. Further, this broadening is tightly correlated with changes in other spectral features, so that the set of ANLs comprises a distinct population difficult to explain with the current quasar standard model. The most striking feature of ANLs is a strong correlation between narrow H\beta\ width and the width of the broad component of the H\beta\ emission line. Another feature of ANLs is a diminished [O II] line, which might indicate a connection between ANLs and the interstellar mediums of their host galaxies, through reduced photoionization or star formation.
