High metal content of highly accreting quasars: Analysis of an extended sample

Abstract

Context. We present an analysis of UV spectra of quasars at intermediate redshifts believed to belong to the extreme Population A (xA), aimed to estimate the chemical abundances of the broad line emitting gas. We follow the approach described in a previous work, extending the sample to 42 sources. Aims. Our aim is to test the robustness of the analysis carried out previously, as well as to confirm the two most intriguing results of this investigation: evidence of very high solar metallicities and a deviation of the relative abundance of elements with respect to solar values. Methods. The basis of our analysis are multicomponent fits in three regions of the spectra centered at 1900, 1550, and 1400 Å in order to deblend the broad components of Aliiiλ1860, Ciii]λ1909, Civλ1549, Heiiλ1640, and Siivλ1397 + Oiv]λ1402 and their blue excess. Results. By comparing the observed flux ratios of these components with the same ratios predicted by the photoionization code CLOUDY, we found that the virialized gas (broad components) presents a metallicity (Z) higher than 10Z . For nonvirialized clouds, we derived a lower limit to the metallicity around ∼ 5Z under the assumption of chemical composition proportional to the solar one, confirming the previous results. We especially relied on the ratios between metal lines and Heiiλ1640. This allowed us to confirm systematic differences in the solar-scaled metallicity derived from the lines of Aluminum and Silicon, and of Carbon, with the first being a factor ≈ 2 higher. Conclusions. For luminous quasars accreting at high rates, high Z values are likely, but Z-scaled values are affected by the possible pollution due to highly-enriched gas associated with the circumnuclear star formation. The high-Z values suggest a complex process involving nuclear and circumnuclear star formation and an interaction between nuclear compact objects and an accretion disk, possibly with the formation of accretion-modified stars.

Metal Content in Relativistically Jetted and Radio-Quiet Quasars in the Main Sequence Context

“…there is an important difference in properties at the extremes of the E1 MS: here, we focused only on the low-R FeII extreme deriving subsolar metallicity. However, highly supersolar Z estimates were derived at the other end of the MS, with R FeII 1 [33,34].…”

“…The lines emitted from ionic species of silicon and aluminum deserve special attention-they are two elements greatly enhanced in supernova ejecta [32]. This approach has yielded tight constraints, especially for sources radiating at high Eddington ratio [29,33,34], where physical properties are consequently well constrained because they converge toward an extreme.…”

“…Each value in this table has been normalized by the corresponding component of Hβ. Error analysis has been performed empirically or on the basis of previous analyses (Hβ and FeII: [19,41]; CIV: [42]; blend at 1900 Å: [34,41]; NV: [33]). The undetected HeII BC was considered in the models to be HeII/Hβ 0.1.…”

Oxygen abundances in the narrow line regions of Seyfert galaxies and the metallicity-luminosity relation

“…Nagao et al 2006;Dors et al 2019), hence 𝑍 BLR estimates at all redshifts are higher by a factor of 2-15 times 𝑍 NLR (e.g. Hamann & Ferland 1993;Baldwin et al 2003b;Bentz et al 2004;Tang et al 2019;Garnica et al 2022), which indicates that the 𝑍 BLR is not representative of the metallicity of the host galaxy, which is better traced by the 𝑍 NLR . Although the BLRs are located in objects with high mass, where high metallicity values are expected (e.g.…”

The Influence of Disk Composition on the Evolution of Stars in the Disks of Active Galactic Nuclei

“…Stars may also enrich AGN disks with metals, at least when those stars are able to reach later stages of nuclear burning, especially if those stars end their lives as supernovae (e.g., Artymowicz et al 1993;Dittmann et al 2021). Spectroscopic measurements suggest that quasar broad-line regions have metallicities at least a few times the solar value with negligible evolution over cosmic time (e.g., Juarez et al 2009;Xu et al 2018;Onoue et al 2020;Garnica et al 2022;Lai et al 2022;Wang et al 2022). Additionally, studies have found that AGN broad-line region metallicity correlates with supermassive black hole (SMBH) mass, suggesting that chemical enrichment is tied to SMBH growth (e.g., Matsuoka et al 2009;Xu et al 2018;Wang et al 2022).…”