tokens: as well, e.g. CALIFA, MaNGA, and SAMI (Croom et al. 2012 ); but the ∼10 times higher spatial resolution of the MAD data boosts the ability to disentangle the different components, in addition to providing information on scales that are still largely unexplored in terms of a systematic study as a function of the location on the SFMS. 4.1 Resolved BPT diagrams We use the well-known [O iii ]/H β versus [N ii ]/H α Baldwin, Phillips Terlevich (hereafter BPT; Baldwin, Phillips Terlevich 1981 ) diagram to identify regions within the galaxies that are ionized by UV radiation from newly born stars (regions of star formation – hereafter, the SF gas) and regions that are ionized by AGN-emitted radiation, shocks, or AGB stars. In these diagrams (e.g. Fig. 1 ), the upper, solid line is the photoionization model of Kewley et al. ( 2001 ), which defines the upper envelope of the region of parameter space occupied by extreme starbursts; this line is a conservative boundary between SF gas and AGN/shocks. The lower, dashed line shows an equivalent but empirical demarcation derived by Kauffmann et al. ( 2003 ). The area of BPT parameter space that lies between these two lines is regarded as identifying regions of gaseous emission with an intermediate ionization spectrum. Figure 1. BPT diagram of all the spaxels from all the galaxies in the sample. The colour scheme has been selected as a continuous variation from purple/blue (SF) to red (AGN/shock dominated), using the η parameter. To explain how η is defined, we compute the minimum distances ( d 1 , d 2 , and d 3 ) of three general points (P 1 , P 2 , and P 3 , respectively, each one in a different region of the BPT diagram) to the two lines that define the three BPT regions. The spaxels with EW(H α)6 Å lie inside the dash–dot area (see the text). It is also well known that the EW is an extra proxy to constrain the possible ionization source of the ionized gas, restricting the SF regions to those with EW(H α) > 6 Å (e.g. Cid Fernandes et al. 2011 ; Sánchez et al. 2014 ; Barrera-Ballesteros et al. 2016 ; Belfiore et al. 2017 ). The EW(H α) is measured by dividing the H α intensity by the flux density of the underlying continuum of the emission line-free spectra, computed as the mean flux density of two windows of 30 Å wide and centred at ±60 Å from the observed H α wavelength. The spaxels with EW(H α) 6 Å are presented in Fig. 1 as those inside the dash–dotted area. The ratio between all the spaxels with EW(H α) 6 Å and all the spaxels under the empirical SF demarcation of the BPT is 4 per cent. Although this ratio is lower than 2 per cent for 24 out of 38 galaxies, it is significant for some galaxies such as NGC 3521 (23 per cent), IC5273 (11 per cent), or NGC 4941 (8 per cent). To obtain a single-valued continuous parameter that conveys the location of each spaxel on its galaxy’s BPT diagram, we define the variable η as either ( i ) the inward-pointing orthogonal distance from the dashed line, identifying SF
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