Abstract The optical spectrum of SDSS J022119.84 + 005628.4 (RA = 02h21m19.84 s, Dec = 00o56' 28".4, J2000; z=0.399785 ± 0.000558) is analyzed by multi-component profile modelling. The small flux ratio of [O III]NC/H β (=0.78) and {FWHM}( {H}\beta {BC}})= {1778.1± 85.9\ km\ s-1} led us to identify SDSS J022119.84 + 005628.4 as a Narrow-line Seyfert 1 galaxy with RFe=1.4+1.0-1.0 and intermediate radio loudness, log R =1.93. The continuum low jump at the Balmer limit might be contributed by a starburst component, which suggests that the object is a relatively young AGN with star-formation activity in its inner region. This provides a useful observational test of the AGN evolution. The low flux ratio of the narrow components, [ {&ion;{O}{iii}}]/ {H}β = 1.62, and the prominent [O II]λ3727 emission, [O II]/[O III] = 2.24, suggests that there should be a group of AGNs different from Seyfert 2s when their broad line regions are obscured by the torus on the line of sight. A possible orientation effect is suggested to interpret the observed Seyfert 1.5s-like spectrum of the object. The spectrum features prominent broad blue wings of both [O III] λλ4959 and 5007. After excluding other possible contributions, we conclude that the broad components are emitted by [O III] itself. The material emitting the broad [O III] line is probably situated in a transient line region (with a low electron density, ne < 107 cm-3) between the broad line region (BLR) and the narrow line region (NLR). The object can be classified as a ``blue outlier'' defined by Zamanov et al., according to its velocity shift \upsilonr {([&ion;{O}{iii}])=-293.6&pm18;.0\ km\ s-1}, relative to the systematic velocity.

Keywords galaxies: active --- galaxies: Seyfert --- quasars: individual (SDSS J022119.84 + 005628.4)

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