Chemical Abundances in Broad Emission Line Regions: The “Nitrogen‐loud” Quasi‐Stellar Object Q0353−383

Abstract

The intensity of the strong N v 1240 line relative to C iv 1549 or to He ii 1640 has been proposed as an indicator of the metallicity of quasi-stellar object (QSO) broad emission line regions, allowing abundance measurements in a large number of QSOs out to the highest redshifts. Previously, it had been shown that the (normally) much weaker lines N iii] 1750 and N iv] 1486 could be used in the same way. The redshift 1.96 QSO 0353À383 has long been known to have N iii] and N iv] lines that are far stronger relative to Ly or C iv than in any other QSO. Because in this particular case these intercombination lines can be easily measured, this unusual object provides an ideal opportunity for testing whether the N v line is a valid abundance indicator. Using new observations of Q0353À383 made both with the Hubble Space Telescope in the ultraviolet and from the ground in the visible passband, we have carefully remeasured the emission lines and reanalyzed their strengths using the latest models of the QSO broad emission line region. We find that intensity ratios involving the strengths of N v, N iv], and N iii] relative to lines of He, C, and O all indicate that nitrogen is overabundant relative to oxygen in Q0353À383 by a factor of $15 compared to solar ratios. This agreement among the diagnostics supports the use of these lines for measuring broad emission line region chemical abundances. If nitrogen behaves like a secondary element, such that N=O / O=H, then the extreme nitrogen enhancement in Q0353À383 implies a metallicity of $15 times the solar value. Even if Q0353À383 represents an extreme outlier in the N=O / O=H relation, the overall metallicity should still be at least 5 times solar. Unusually high metallicities in Q0353À383 might imply that we caught this object just as the gas-phase metallicity in the central part of its host galaxy has peaked, at a time when the interstellar gas supply is nearly exhausted and hence the fuel source for the central QSO is ready to shut off.

Abundance anomalies in tidal disruption events

“…Peterson 1997). The challenge is that, at least for Q0353−383, the anomalous spectra can persist for decades (Osmer 1980, Baldwin et al 2003. The time scale problem from §2 is now reversed, in that we would now like longer orbital time scales than years to decades.…”

The unusual N IV] -emitter galaxy GDS J033218.92-275302.7: star formation or AGN-driven winds from a massive galaxy atz= 5.56

“…This has already been done by several authors (e.g. Baldwin et al 2003;Glikman et al 2007;Jiang et al 2008 As performed in Glikman et al (2007), since the blue side of the line profile is absorbed, we forced the symmetry in the line by mirroring the red side of the line profile over the peak wavelength and computed the Gaussian fit. The narrow-line component increases to ∼750 km s −1 .…”

Ly$\mathsf{\alpha}$ emitters in the GOODS-S field

“…It is also sometimes detected in AGN and quasar spectra but with an intensity that is low with respect to lines such as C iv and N v, although there are rare examples of "Nitrogen Loud" quasars that exhibit unusually strong nitrogen lines, e.g. Baldwin et al (2003). At a redshift of 3.4, the Lynx arc (Fosbury et al 2003, hereafter F03), is known to show N iv] with a strength comparable to other UV intercombination lines such as O iii] and C iii] and the resonance doublet C iv.…”