Sdss-Iv Manga: Modeling The Spectral Line-Spread Function To Subpercent Accuracy

The Sloan Digital Sky Survey IV Mapping Nearby Galaxies at APO (MaNGA) program has been operating from 2014 to 2020, and has now observed a sample of 9269 galaxies in the low redshift universe (z similar to 0.05) with integral-field spectroscopy. With rest-optical (lambda lambda 0.36-1.0 mu m) spectral resolution R similar to 2000 the instrumental spectral line-spread function (LSF) typically has 1 sigma width of about 70 km s(-1), which poses a challenge for the study of the typically 20-30 km s(-1) velocity dispersion of the ionized gas in present-day disk galaxies. In this contribution, we present a major revision of the MaNGA data pipeline architecture, focusing particularly on a variety of factors impacting the effective LSF (e.g., under-sampling, spectral rectification, and data cube construction). Through comparison with external assessments of the MaNGA data provided by substantially higher-resolution R similar to 10,000 instruments, we demonstrate that the revised MPL-10 pipeline measures the instrumental LSF sufficiently accurately (<= 0.6% systematic, 2% random around the wavelength of H alpha) that it enables reliable measurements of astrophysical velocity dispersions sigma(H alpha) similar to 20 km s(-1) for spaxels with emission lines detected at signal-to-noise ratio > 50. Velocity dispersions derived from [O II], H beta, [O III], [N II], and [S II] are consistent with those derived from H alpha to within about 2% at sigma(H alpha) > 30 km s(-1). Although the impact of these changes to the estimated LSF will be minimal at velocity dispersions greater than about 100 km s(-1), scientific results from previous data releases that are based on dispersions far below the instrumental resolution should be reevaluated.