Nucleosynthesis Contribution of Neutrino-dominated Accretion Flows to the Chemical Evolution of Active Galactic Nuclei

Abstract

Recent observations of quasars show high line-flux ratios in their broad emission lines and the ratios appear to be independent of redshift up to z ≳ 6, which indicates that the broad-line regions of these early quasars are surprisingly metal-rich. Here, we revisit the chemical evolution of high-redshift quasars by adding a new ingredient, i.e., the neutrino-dominated accretion flows (NDAFs) with outflows, on top of the conventional core-collapse supernovae (CCSNe). In the presence of the chemical contribution from NDAFs with outflows, the total metal mass (i.e., the summation of the conventional CCSN and NDAFs with outflows) per CCSN depends weakly upon the mass of the progenitor star if the mass is in the range of ∼25–55 M ⊙. We model the chemical evolution by adopting a improved open-box model with three typical initial mass functions (IMFs). We find that, with the additional chemical contribution from NDAFs with outflows, the quasar metallicity can be enriched more rapidly in the very early universe (z ∼ 10) and reaches a higher saturation than the no-NDAF case at z ∼ 8, after which they evolve slowly with redshift. The quasar metallicity can reach ∼20 Z ⊙ (Z ⊙ denotes the metallicity of the Sun, ∼20% of which is produced by NDAF outflows) at z ∼ 8 for the “top-heavy” IMF model in Toyouchi et al., which readily explains the quasar observations on the supersolar metal abundance and redshift-independent evolution.

In Situ Star Formation in Accretion Disks and Explanation of Correlation between the Black Hole Mass and Metallicity in Active Galactic Nuclei

“…We found that a standard IMF with Γ = 2.35 predicts a much shallower M BH −Z BLR correlation, which cannot explain the observed correlation (e.g., the green dashed line in the bottom panel of Figure 3). Our results imply a "topheavy" stellar mass distribution; that is, Γ < 1 is needed to reproduce the average M BH −Z BLR relation, which is roughly consistent with the results of Toyouchi et al (2022) and Qi et al (2022). The direct observational constraints on the stellar mass distribution in the galaxy center are difficult due to the limited telescope resolutions.…”

Star Formation in Self-gravitating Disks in Active Galactic Nuclei. III. Efficient Production of Iron and Infrared Spectral Energy Distributions

“…Many thanks are given to RM campaigns (Kaspi et al 2000;Peterson et al 2004;Du et al 2014;Shen et al 2015;U et al 2022;Shen et al 2023), showing that the typical radii of AGN BLRs are of the order of 10 3 ∼ 10 5 R g (where R g is the gravitational radius of the central SMBH; see Figure 6 in Du et al 2016), which is in good agreement with the selfgravitating regions (Goodman 2003;Sirko & Goodman 2003). The idea of star formation is extended to connect with the BLR metallicity by Wang et al (2010Wang et al ( , 2011Wang et al ( , 2012 for properties of metallicity with SMBH masses, accretion rates, and luminosity (see also Qi et al 2022;Fan & Wu 2023). This is also supported by evidence from the correlation between accretion rates and star formation rates (Chen et al 2009;Zhuang & Ho 2020).…”

Contribution of Neutrino-dominated Accretion Flows to the Cosmic MeV Neutrino Background

“…Numerous metalfree and very metal-poor massive stars are formed in the highredshift universe, and the frequency of solar metallicity stars in galaxies would be low in the early universe. The metal-rich stars might form in the central supermassive BH accretion disk and their evolution should contribute to the metallicity of active galactic nuclei (e.g., Qi et al 2022a). In the low-redshift universe, the metallicity of galaxies would be relatively high, but galaxies whose metallicities are about 1 order of magnitude lower than the solar value reside within the redshift z < 1 (Peeples & Somerville 2013).…”