Strong Narrow Fe ii Emission Lines in the Quasar SDSS J102839.11+450009.4

Abstract

We report identification of SDSS J102839.11+450009.4 as a peculiarly interesting quasar. It shows very prominent narrow emission lines (NELs) in Fe n that are remarkably different from the broad Fe n multiplets commonly observed in quasars and Seyfert 1 galaxies. The Fe II NEL spectrum is dominated in the UV by transitions to the low-lying ground levels with even parity, and by forbidden transitions in the optical, suggesting its formation in a warm collisionally ionized low density medium. Comparison with photoionization models suggests that fluorescence of Fe n by a soft continuum is probably also important in explaining the intensity ratios within the Fe II NEL multiplets and that of Fe II to S II λ4047 NELs. The Fe II NELs have similar widths to other NELs, including [O III] and [O II] , but are blueshifted by ∼ 170 km s -1 with respect to the redshift of the latter, which we take to be the systemic redshift of the quasar. In addition to the unusual Fe II NELs, the SDSS spectrum also reveals narrow absorption lines (NALs) in Hβ, Hγ, Hδ, Hei λλ3889, 3189, 2946, 2830, and Mg II λλ2796, 2803. We identify two Mg II NAL systems blueshifted by 1200 and 670 km s -1 , respectively. The redshift of the lower velocity Mg n NAL system is consistent with that of the Balmer and He I NALs. The observed He I NALs require a hydrogen column density of > 10 20 cm -2 in an HII region. Very few quasars show absorption in He I lines, and even fewer in Balmer lines. The unique spectral properties make this quasar a promising probe of the formation of Fe n emission lines and outflows, and the possible relation between the two. © 2008. The American Astronomical Society. All rights reserved.