Projects |

Metallicity Calibrations in AGNs: N₂O₂ and N₂S₂ Diagnostics

Mon, 20 Apr 2026 00:00:00 +0000

Standard strong-line diagnostics are often heavily biased by the intense radiation fields of AGNs. This ongoing project focuses on deriving new metallicity calibrations—specifically utilizing the N₂O₂ and N₂S₂ emission line ratios—that remain unaffected by structural nebular variations. By parameterizing models explicitly by intrinsic 2-10 keV X-ray luminosity, these tools lay the groundwork for analyzing high-resolution spectra from next-generation observatories.

Interactive Calibrations

N₂O₂ Simulator Demonstrating the robustness of the [N ii]/[O ii] ratio against X-ray luminosity variations compared to traditional diagnostics.

N₂S₂ Simulator Illustrating the volume-canceling properties of the [N ii]/[S ii] ratio and its independence from electron density fluctuations.

Identifying AGNs from X-ray Detections: Primary Parameter Calibrations

Tue, 24 Mar 2026 00:00:00 +0000

Traditional strong-line diagnostics often struggle in Active Galactic Nuclei due to complex radiation fields. In this foundational first paper of our series on identifying AGNs from X-ray detections, we developed new metallicity calibrations (such as $\rm N_2$ and $\rm O_3N_2$) that directly account for these structural nebular variations.

By explicitly parameterizing our models using the intrinsic 2-10 keV X-ray luminosity, we successfully decoupled true gas-phase chemical abundances from the intense AGN radiation field, allowing for highly accurate measurements without relying on temperature-dependent optical limitations.

Spatially Resolved Gas-Phase Metallicity

Tue, 01 Oct 2024 00:00:00 +0000

Moving beyond integrated single-fiber spectra, this project utilizes optical Integral Field Unit (IFU) observations from the Gemini Multi-Object Spectrograph (GMOS) and the Multi Unit Spectroscopic Explorer (MUSE) to map the 2D chemical composition of 15 nearby Seyfert galaxies (comprising 9 GMOS and 6 MUSE datasets). By probing the inner few hundred parsecs, this spatially resolved approach reveals exactly how gas-phase metallicity fluctuates within the active nucleus. Specifically, we demonstrate that these local Seyferts exhibit positive (inverted) metallicity radial profiles over extended periods due to seamless gas accretion histories. Furthermore, our spatially resolved data establishes a clear anti-correlation between the central gas-phase metallicity and the AGN’s Eddington ratio.

Interactive IFU Radial Profile Simulator

Compare the steep negative gradient of a normal star-forming control galaxy to the flattened and inverted gradients caused by AGN gas mixing.

Oxygen Abundances & The Metallicity-Luminosity Relation

Fri, 20 Jan 2023 00:00:00 +0000

By systematically analyzing the narrow line regions (NLRs) of Seyfert galaxies, this project explores how actively accreting supermassive black holes influence the gas-phase oxygen abundances in their host environments. Using state-of-the-art photoionization models, we established refined metallicity-luminosity relations crucial for understanding galaxy evolution, specifically noting the anti-correlation driven by AGN feedback.

Interactive M-Z-L Relation Simulator

Simulate the shifts in the Luminosity-Metallicity anti-correlation across varying degrees of AGN feedback strength.

Direct Abundance Determination of Neon

Thu, 16 Sep 2021 00:00:00 +0000

This research bridges the gap between optical and infrared observational datasets. By leveraging multi-wavelength emission lines, this project bypasses traditional temperature-dependent optical limitations, allowing for a more robust and direct measurement of Neon abundances within the complex environments of Seyfert 2 AGNs.

Interactive Neon Abundance Simulator

Explore the temperature dependence of optical derivations versus infrared derivations.

Interactive Figure 5: Nebular Structure Profiles

The interactive plot below reproduces the cloudy photoionization models from our 2021 publication. It compares the internal gas structure of a cloud ionized by an AGN (red solid line, hard X-ray power-law) versus a star-forming H ii region (blue dashed line, stellar SED) across a normalized radius ($R/R_{\rm e}$).

Because the axes are normalized to the total radius of the cloud ($R_{\rm e}$), the physical differences between a Strömgren sphere (H ii) and an extended Partially Ionized Zone (AGN) become starkly apparent. By plotting the fractional abundances and electron temperature, this figure demonstrates exactly why traditional H ii region assumptions fail when applied to AGNs:

Bottom Panel (Electron Temperature, $T_{\rm e}$): The AGN model exhibits a very distinct temperature distribution compared to the H ii region, showing a stronger decrease with the radius. The AGN temperature curve doesn’t just rise at the inner radius. The AGN temperature actually starts from a peak of nearly $1.4 \times 10^4$ K at the inner radius, dips down in the middle zone and intersects the H ii region temperature model curve at $\sim$$0.88 \times 10^4$ K, and finally drops to $\sim$$0.4 \times 10^4$ K where it intersects once again with the H ii region temperature model curve at the outer region. In stark contrast, the H ii temperature remains a completely flat $\sim$$0.85 \times 10^4$ K.
Middle & Top Panels (O²⁺/O and Ne²⁺/Ne): In the H ii region model, both ionic ratios show similar distributions along the radius, confirming the standard assumption that $T_{\rm e}$(O iii) $\approx$ $T_{\rm e}$(Ne iii). In the AGN model, however, the Ne²⁺/Ne ionic abundance extends significantly further into the outer nebular radius (where the temperature is lower) in comparison to the O²⁺/O abundance. While O²⁺ drops off rapidly, Ne²⁺ persists throughout the cooler regions of the cloud.
The Critical AGN Deviation: In the AGN model, the Ne²⁺/Ne ionic abundance extends to an outer nebular radius (where the temperature is lower) in comparison to the O²⁺/O abundance. Because Ne²⁺ exists in a distinct, cooler outer region compared to O²⁺, the assumption that $T_{\rm e}$(O iii) $\approx$ $T_{\rm e}$(Ne iii) is strictly invalid for AGNs. Furthermore, this structural difference clearly indicates that the standard assumption used in H ii regions, (Ne²⁺/O²⁺) = (Ne/O), cannot be applied to AGNs.