SDSS-IV MaNGA: Modeling the spectral line-spread function to subpercent accuracy

Abstract

<p>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 (<em>z</em> ∼ 0.05) with integral-field spectroscopy. With rest-optical (<em>λλ</em>0.36–1.0 <em>μ</em>m) spectral resolution <em>R</em> ∼ 2000 the instrumental spectral line-spread function (LSF) typically has 1<em>σ</em> width of about 70 km s<sup>−1</sup>, which poses a challenge for the study of the typically 20–30 km s<sup>−1</sup> 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 <em>R</em> ∼ 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<em>α</em>) that it enables reliable measurements of astrophysical velocity dispersions <em>σ</em><sub>H<em>α</em></sub> ∼ 20 km s<sup>−1</sup> for spaxels with emission lines detected at signal-to-noise ratio > 50. Velocity dispersions derived from [O II], H<em>β</em>, [O III], [N II], and [S II] are consistent with those derived from H<em>α</em> to within about 2% at <em>σ</em><sub>H<em>α</em></sub> > 30 km s<sup>−1</sup>. Although the impact of these changes to the estimated LSF will be minimal at velocity dispersions greater than about 100 km s<sup>−1</sup>, scientific results from previous data releases that are based on dispersions far below the instrumental resolution should be reevaluated.</p>

Topics & Concepts