Work

SDSS-IV MaNGA: Data-model discrepancy in temperature-sensitive line ratios for star-forming galaxies

Year: 2025

Type: article

Abstract: Aims . Gas-phase metallicity is a fundamental parameter that helps constrain the star-forming history and chemical evolution of a galaxy. Measuring the electron temperature through auroral-to-strong line ratios is a direct approach to deriving metallicity. However, there is a longstanding discrepancy between metallicity measured through the direct method and that based on the photoionization models. This paper aims to verify and understand the discrepancies. Methods . We binned ~1.5 million spaxels from SDSS-IV MaNGA according to metallicity and ionization parameters derived from theoretical strong-line calibrations. We stacked the spectra of spaxels within each bin and measured the flux of strong lines and faint auroral lines. Auroral lines for [O II ], [S II ], [O III ], and [S III ] were detected in the stacked spectra of most bins, and the [N II ] auroral line was detected in fewer bins. We applied an empirical method to correct dust attenuation, which makes more realistic corrections for low ionization lines. Results . We derived electron temperatures for these five ionic species and measured the oxygen and sulfur abundances using the direct method. We present the resulting abundance measurements and compare them with those model-calibrated strong-line abundances. The chemical abundances measured with the direct method are lower than those derived from the photoionization model, with a median of 0.09 dex. This discrepancy is smaller compared to the results based on other theoretical metallicity calibrations previously reported. However, we notice that the direct method could not account for the variation in ionization parameters, indicating that the precise calibration of metallicity using the direct method has yet to be fully realized. We report significant discrepancies between data and the photoionization model, which illustrates that the 1D photoionization model is incapable of representing the complexity of real situations, and cannot predict the increase in the auroral-to-strong line ratio of [O II ] at high metallicity.

Source: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/202556301

Authors: Ziming Peng, Renbin Yan, Xihan Ji, Zesen Lin, Man-Yin Leo Lee

Institutions: Chinese University of Hong Kong, University of Cambridge, University of California San Diego

Language: English

Topic: Galaxies: Formation, Evolution, Phenomena

Subfield: Astronomy and Astrophysics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $1,865

Funders: National Natural Science Foundation of China, Innovation and Technology Commission - Hong Kong, Science and Technology Facilities Council