Near‐Infrared Spectroscopy of High‐Redshift Active Galactic Nuclei. II. Disappearing Narrow‐Line Regions and the Role of Accretion

We present new near infrared spectroscopic measurements for 29 luminoushigh-z quasars and use the data to discuss the size and other properties of theNLRs in those sources. The high resolution spectra have been used to carefullymodel the Fe II blends and to provide reliable [O III], Fe II and Hbmeasurements. We find that about 2/3 of all high luminosity sources show strong[O III] lines while the remaining objects show no or very weak such line. Whileweak [O III] emitters are also found among lower luminosity AGN, we argue thatthe implications for very high luminosity objects are different. In particular,we suggest that the averaging of these two populations in other works gave riseto claims of a Baldwin relationship in [O III] which is not confirmed by ourdata. We also argue that earlier proposed relations of the type R_NLR \proptoL_[O III]^{1/2}, where R_NLR is the NLR radius, are theoretically sound yetthey must break down for R_NLR exceeding a few kpc. This suggests that the NLRproperties in luminous sources are different from those observed in nearby AGN.In particular, we suggest that some sources lost their very large, dynamicallyunbound NLR while others are in a phase of violent star-forming events thatproduce a large quantity of high density gas in the central kpc. This gas isionized and excited by the central radiation source and its spectroscopicproperties may be different from those observed in nearby, lower luminosityNLRs. We also discuss the dependence of EW(Hb) and Fe II/Hb on L, M_BH, andaccretion rate for a large sample of AGNs. The strongest dependence of the twoquantities is on the accretion rate and the Fe II/Hb correlation is probablydue to the EW(Hb) dependence on accretion rate. We show the most extreme valuesmeasured so far of Fe II/Hb and address its correlation with EW([O III]).Comment: 10 pages (emulateapj), 9 figures. Accepted by Ap