for detections. It works fine for point source or barely resolved source. For extended radio source that is detected as multiple objects by <span style="font-variant:small-caps;">sfind</span>, we add up the flux densities of individual components as total flux density. We combine the background uncertainty and the Gaussian fitting uncertainty calculated by <span style="font-variant:small-caps;">sfind</span>.

### Aperture flux density

As a large fraction of our galaxies are extended sources, it is possible that <span style="font-variant:small-caps;">sfind</span> misses some flux density. For comparison, we measure the total flux density within a given aperture, if available, to better account for the extended emission. The aperture is based on the B band 25 $\mathrm{mag/arcsec}^2$ isophotal ellipse, taken from the surface photometry catalogue of the ESO-Uppsala galaxies [@1989spce.book.....L]. If the B band aperture is not available, we use WISE 3.4[$\,\mathrm{\mu m}$]{} 1-$\sigma$ isophotal ellipse [see @2017MNRAS.472.3029W]. There are 62 LVHIS galaxies with available B band aperture, and 17 with a WISE aperture (see Table \[tab:flux\]). As the synthesis beam size varies dramatically from galaxy to galaxy, we convolve the ellipse with the beam shape (2 times the major and minor axes, respectively) in order to enlarge the aperture to make sure we do not miss radio flux (therefore, 