blue galaxies, in which the grayscale two-dimensional histogram demonstrates the number density (crowdedness) of spaxels and the white contours cover the $85\%$ of our final sample spaxels. The solid and dashed lines are the demarcations between star-forming galaxies (SFGs) and AGNs defined by [@Kauffmann2003] and [@Kewley2001], respectively.

Determinations of Metallicity and Other Physical Properties {#subsec:metallicity}
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The electron temperature ($T_e$) method is generally deemed as the most reliable approach for deriving metallicity, which is based on the ratios of faint auroral-to-nebular emission lines [@Lin2017], such as ${\hbox{[O\,{\sc iii}]}}\lambda4363/{\hbox{[O\,{\sc iii}]}}\lambda5007$. However, only a handful of spaxels show pronounced ${\hbox{[O\,{\sc iii}]}}\lambda4363$ lines. Besides, variety of calibrators can also be used to estimate the metallicity [@Kewley2008]. Based on the photoionization models for ${\hbox{H\,{\sc ii}}}$ regions, these emission line ratios, like $({\hbox{[O\,{\sc ii}]}}\lambda3727+{\hbox{[O\,{\sc iii}]}}\lambda\lambda4959,5007)/{\hbox{H$\beta$}}$ [R23, @Kobulnicky04], ${\hbox{[N\,{\sc ii}]}}\lambda6583/{\hbox{[O\,{\sc ii}]}}\lambda3727$ [N2O2, @Kewley2002], can be used as the calibrators to reproduce the metallicity. Some other diagnostics, like $({\hbox{[O\,{\sc iii}]}}\lambda5007/{\hbox{H$\beta$}})/({\hbox{[N\,{\sc ii}]}}\lambda6583/{\hbox{H$\alpha$}})$ and ${\hbox{[N\,{\sc ii}]}}\lambda6583/{\hbox{H$\alpha$}}$ [O3N2, N2, @Pettini2004], are calibrated by empirical fitting to the electronic temperature ($T_e$) method with strong-line ratios for ${\hbox{H\,{\sc ii}}}$ regions and galaxies. However, there is a large discrepancy between the metallicities derived by different calibrators [@Kehrig2013; @Morisset2016]. For example, compared with the 