We measured the emission lines in the spaxel spectra of MaNGA ( Mapping Nearby Galaxies at Apache Point Observatory ) galaxies in order to determine the abundance distributions therein .
It has been suggested that the strength of the low-ionization lines , R _ { 2 } , N _ { 2 } , and S _ { 2 , } may be increased ( relative to Balmer lines ) in ( some ) spaxel spectra of the MaNGA survey due to a contribution of the radiation of the diffuse ionized gas .
Consequently , the abundances derived from the spaxel spectra through strong-line methods may suffer from large errors .
We examined this expectation by comparing the behaviour of the line intensities and the abundances estimated through different calibrations for slit spectra of H ii regions in nearby galaxies , for fibre spectra from the Sloan Digital Sky Survey ( SDSS ) , and for spaxel spectra of the MaNGA survey .
We found that the S _ { 2 } strength is increased significantly in the fibre and spaxel spectra .
The mean enhancement changes with metallicity and can be as large as a factor of \sim 2 .
The mean distortion of R _ { 2 } and N _ { 2 } is less than a factor of \sim 1.3 .
This suggests that Kaufmann et al. ’ s demarcation line between active galactic nuclei ( AGNs ) and H ii regions in the Baldwin , Phillips , & Terlevich ( BPT ) diagram is a useful criterion to reject spectra with significantly distorted strengths of the N _ { 2 } and R _ { 2 } lines .
We find that the three-dimensional R calibration , which uses the N _ { 2 } and R _ { 2 } lines , produces reliable abundances in the MaNGA galaxies .
The one-dimensional N2 calibration produces either reliable or wrong abundances depending on whether excitation and N/O abundance ratio in the target region ( spaxel ) are close to or differ from those parameters in the calibrating points located close to the calibration relation .
We then determined abundance distributions within the optical radii in the discs of 47 MaNGA galaxies .
The optical radii of the galaxies were estimated from the surface brightness profiles constructed based on the MaNGA observations .