SDSS-IV MaNGA: Modeling the Spectral Line-spread Function to Subpercent Accuracy
David R. Law, Kyle B. Westfall, Matthew A. Bershady, Michele Cappellari, Renbin Yan, Francesco Belfiore, Dmitry Bizyaev, Joel R. Brownstein, Yanping Chen, Brian Cherinka, Niv Drory, Daniel Lazarz, Shravan Shetty
Abstract
Abstract 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 ∼ 0.05) with integral-field spectroscopy. With rest-optical ( λλ 0.36–1.0 μ m) spectral resolution R ∼ 2000 the instrumental spectral line-spread function (LSF) typically has 1 σ 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 ∼ 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 α ) that it enables reliable measurements of astrophysical velocity dispersions σ H α ∼ 20 km s −1 for spaxels with emission lines detected at signal-to-noise ratio > 50. Velocity dispersions derived from [O II ], H β , [O III ], [N II ], and [S II ] are consistent with those derived from H α to within about 2% at σ H α > 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.