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CHAOS VII — Strong Line Abundances: Improving Empirical Gas-Phase Abundance Diagnostics with Expanded Parameter Space Calibrations

Presentation #153.03 in the session “Molecular Clouds, HII Regions, Interstellar Medium”.

Published onJan 11, 2021
CHAOS VII — Strong Line Abundances: Improving Empirical Gas-Phase Abundance Diagnostics with Expanded Parameter Space Calibrations

Chemical abundances of HII regions have historically been calculated using either the Te-based direct method, or the strong-line method, which relies on calibrating strong emission-line ratios to theoretical or empirical abundance determinations. These strong-line calibrations allow abundance trends to be measured in galaxy populations where the direct method is too weak. In regions where abundances can be found with both methods, calculated values often do not agree. As strong-line calibrations serve as the best tool to infer the chemical evolution of the distant universe, reducing this discrepancy and understanding the underlying biases introduced by different methods is crucial. We present an analysis of 11 strong-line calibrations and find the calibrations by Pettini & Pagel (2004) and the sulfur-based calibration by Pilyugin & Grebel (2016) to correlate closest with direct method abundances from 202 HII regions in the CHAOS Survey. Secondary trends observed in N/O as well as S/O abundance suggest normalization based on these parameters may further reduce discrepancy.


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