In:
The Astrophysical Journal, American Astronomical Society, Vol. 926, No. 1 ( 2022-02-01), p. 55-
Abstract:
We present new and archival SOFIA FIFI-LS far-IR spectroscopic observations of the [O iii ] 52 μ m and/or the [N iii ] 57 μ m lines of 25 local galaxies. Including 31 other galaxies from Herschel-PACS, we discuss a local sample of 47 galaxies, including the H ii galaxies, luminous IR galaxies, low-metallicity dwarfs, and Seyfert nuclei. Analyzing the mid- to far-IR fine-structure lines of this sample, we assess the metallicity and compare it with the optical spectroscopy estimates. Using the IR, we find an O/H–N/O relation similar to that known in the optical. Conversely, we find systematically lower N/O IR abundances when compared to the optical determinations, especially at high values of N/O ( log ( N / O ) 〉 −0.8). We explore various hypotheses to account for this difference: (i) difference in ionization structure traced by optical (O + , N + regions) versus IR lines (O 2+ , N 2+ regions), (ii) contamination of diffuse ionized gas affecting the optical lines used to compute the N/O abundance, and (iii) dust obscuration affecting the optical-based determinations. However, we have not found any correlation of Δ ( N / O ) = ( N / O ) OPT − ( N / O ) IR with ionization, or electron density, or optical extinction. We speculatively suggest that the accretion of metal-poor gas from the circumgalactic medium could provide an explanation for this difference because the rapid decrease of total abundances during infall is followed by a N/O ratio decrease due to the primary production of young—possibly embedded—massive stars, which are preferentially traced by the IR diagnostics, while optical diagnostics would better trace the secondary production, when both N/O and O/H abundance ratios increase.
Type of Medium:
Online Resource
ISSN:
0004-637X
,
1538-4357
DOI:
10.3847/1538-4357/ac37b7
Language:
Unknown
Publisher:
American Astronomical Society
Publication Date:
2022
detail.hit.zdb_id:
2207648-7
detail.hit.zdb_id:
1473835-1
SSG:
16,12
