The MAGPI Survey: Emission Line Products Data Release and the Role of Spectroscopic Aperture Covering Fraction on the Balmer Decrement-Stellar Mass Relation

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Abstract The Middle Ages Galaxy Properties with Integral field spectroscopy (MAGPI) survey is a Large Program on the European Southern Observatory Very Large Telescope using the MUSE instrument. This paper presents the data release for the MAGPI emission line products and includes emission line maps for 836 galaxies at 0.05 ≤ zspec ≤ 0.424 (Hα-window) and aperture-based emission line measurements for 2,607 galaxies at 0.05 ≤ zspec ≤ 1.50 (upper bound is [OII] cut-off), both based on the GIST software, for all 56 MAGPI fields. We use these data to examine dust attenuation, which represents a major source of uncertainty in the derived properties of galaxies that are critical to constrain models of galaxy evolution. We examine the role that the spectroscopic aperture covering fraction (fc) has on the relationship between the Balmer decrement (BD = F(Hα)/F(Hβ); a common proxy for dust attenuation) and the total stellar mass (M⋆). Several studies have suggested that the BD-M⋆ relation may be redshift invariant; however, the compared surveys often have different fc due to their differing fibre or slit sizes that can cause systematic offsets. Our results indicate that fc has a significant impact on this relationship, due to galaxies having negative BD radial gradients, which are more negative for more massive galaxies at z ≲ 0.4. Comparing spectroscopic surveys with ≳0.5, we find that the BD-M⋆ relation shows a preference for redshift evolution and is roughly consistent with the behaviour of UV stellar continuum attenuation redshift evolution (AFUV-z), with the average dust attenuation in galaxies peaking at z ~ 1.2 and decreasing at lower and higher redshifts.

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