formation regions
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Observations and data reduction
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The sample of galaxies is based on our photometric survey of 26 galaxies [@gusev2015]. We selected nine of them (NGC 266, NGC 628, NGC 2336, NGC 3184, NGC 3726, NGC 5585, NGC 6217, NGC 6946, and NGC 7331) with observed star formation regions and available H$\alpha$ spectrophotometric data.

Our own photometric $UBVRI$ and H$\alpha$ (H$\alpha$+\[N[ii]{}\]) observations were described and published earlier [see @gusev2018 and references therein].

We did not observe NGC 3184 from our sample in $U$ filter. Therefore we used an $U$ image of NGC 3184 obtained by @larsen1999b and available in the NED[^1] database. The absolute calibration of the $U$ image of the galaxy was carried out using parameters of descriptors from original FITS files (images) and their explanations in @larsen1999b. Additionally, we checked the calibration using the aperture photometry data for the galaxies from the LEDA[^2] database [@paturel2003]. We also compared our $BVRI$ images of NGC 3184 with those from @larsen1999b. Pixel-to-pixel deviations are within the stated accuracy of measurements and they did not show any systematic errors.

We also used H$\alpha$+\[N[ii]{}\] FITS images of NGC 3726 and NGC 5585 obtained by @knapen2004 and @dale2009. Parameters for absolute calibration 