the actual photometry aperture is slightly larger than the optical aperture listed in Table \[tab:flux\]). We subtract nearby sources within the aperture but not associated with our target galaxy. We manually identify the deconvolution model components of these sources, subtract models from the visibility data, remake the radio image and measure the aperture flux density. This minimizes the neighbour contamination to our flux density measurement.

![image](fig/cont_snr.pdf){width="8cm"}

The aperture flux density uncertainty is estimated as $\sigma = \sigma_\mathrm{bkg} \sqrt{2A_\mathrm{aper} / A_\mathrm{beam}}$. Here $\sigma_\mathrm{bkg}$ is the rms value of the background, as described above. $A_\mathrm{aper}$ is the size of the aperture in unit of pixels. $A_\mathrm{beam}$ is the size of the synthesis beam in unit of pixels[^3]. Figure \[fig:aper\_snr\] shows the measured signal-to-noise ratio as a function of measured aperture flux density. As aperture flux density is an integration of all pixel values within the aperture, it is expected to get negative ones simply due to statistical fluctuation for weak sources. The objects with negative flux densities are shown as red symbols with their absolute values. Negative flux densities are all well below 3-$\sigma$. Therefore we use a minimum signal-to-noise ratio of 3 to define a detection.

### Comparison

![image](fig/cont_sfind_aper.pdf){width="8cm"}

In Figure 