BRIEF RESEARCH REPORT article
Front. Astron. Space Sci.
Sec. Extragalactic Astronomy
Volume 12 - 2025 | doi: 10.3389/fspas.2025.1540522
This article is part of the Research TopicBroad-Band Spectral Energy Distributions in AGNs - Advances and the FutureView all 5 articles
Ratios of Forbidden [OIII]λλ4959,5007 and [NII]λλ6548,6583 Lines in Nearby Narrow Emission Line Galaxies
Provisionally accepted
- 1Astronomical Observatory, Belgrade, Serbia
- 2Osservatorio Astronomico di Padova (INAF), Padua, Veneto, Italy
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Galaxies with narrow emission lines play a crucial role in testing the theoretical values of transition probabilities, especially for lines that need conditions that are hard to produce in laboratory plasma, and hence the theoretical values could not be checked in experimental measurements. In this paper, we explore the [O III]λλ4959, 5007 and the [N II]λλ6548,6583 doublets and their line ratios in a volume limited samples (0.01 ⩽ z ⩽ 0.05) of Sy2, LINERs, composite objects and star-forming galaxies, that zooms in the central region of these objects. Our results confirm that the theoretical line ratios R([OIII]) = 2.98 and R([N II]) = 3.05 as predicted by Storey & Zeippen (2000) are consistent with observations of HII regions, for both line ratios. This agreement occurs under conditions minimally affected by reddening, corresponding to total-to-selective extinction ratios (RV) between 3.1 and 4.1. In contrast, Seyfert 2, LINER, and composite galaxies confirm the same theoretical prediction of the [OIII] line ratios in the case of stronger reddening (2.1 ≤ RV ≤ 3.1), while [NII] ratios stays slightly lower than predicted by Storey & Zeippen (2000), aligning more closer to the values reported by Galavis et al. (1997), or indicating a presence of environmental conditions that affects these line ratios. This discrepancy in [NII] ratios suggests that, beyond reddening effects, the physical conditions in the [NII]-emitting regions of active galaxies differ from those in HII regions. Shocks, variations in electron density, ionization mechanisms, and gas or dust composition may contribute to these differences.
Keywords: Galaxies, Emission line galaxies, Seyfert - galaxies, Star forming galaxies, Liners, Active gala×ies, emission lines ratio
Received: 05 Dec 2024; Accepted: 23 Apr 2025.
Copyright: © 2025 Bon, Bon, Marziani and Popovic. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Natasa Bon, Astronomical Observatory, Belgrade, Serbia
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