2025AJ....169...95W

Using data from the Large Area Multi-Object fiber Spectroscopic Telescope Medium-Resolution Spectroscopic Survey of Nebulae, we create a sample of 17,821 diffuse ionized gas spectra in the anticenter region of the Milky Way by excluding fibers in the directions of H II regions and supernova remnants. We then analyze the radial and vertical distributions of three line ratios ([N II]/Hα, [S II]/Hα, and [S II]/[N II]), as well as the oxygen abundance. [N II]/Hα and [S II]/Hα do not exhibit a consistent, monotonic decrease with increasing Galactocentric distance (R_gal). Instead, they show enhancement within the interarm region, positioned between the Local Arm and the Perseus Arm. [S II]/[N II] has a radial gradient of 0.1415 ± 0.0646 kpc^–1 for the inner disk (8.34 < R_gal < 9.65 kpc) and remains nearly flat for the outer disk (R_gal > 9.65 kpc). In the vertical direction, [N II]/Hα, [S II]/Hα, and [S II]/[N II] increase with increasing Galactic disk height (∣z∣) in both southern and northern disks. Based on the N2S2Hα method, which combines [S II]/[N II] and [N II]/Hα, we estimate the oxygen abundance. The oxygen abundance exhibits a consistent radial gradient with R_gal, featuring a slope of -0.0559 ± 0.0209 dex kpc^–1 for the inner disk and a similar slope of -0.0429 ± 0.0599 dex kpc^–1 for the outer disk. A single linear fitting to the entire disk yields a slope of -0.0317 ± 0.0124 dex kpc^–1. In the vertical direction, the oxygen abundance decreases with increasing ∣z∣ in both southern and northern disks.