Spatial Variation in Strong Line Ratios and Physical Conditions in Two
  Strongly-Lensed Galaxies at z~1.4
  For studies of galaxy formation and evolution, one of the major benefits of
the James Webb Space Telescope is that space-based IFUs like those on its
NIRSpec and MIRI instruments will enable spatially resolved spectroscopy of
distant galaxies, including spectroscopy at the scale of individual
star-forming regions in galaxies that have been gravitationally lensed. In the
meantime, there is only a very small subset of lensed sources where work like
this is possible even with the Hubble Space Telescope's Wide Field Camera 3
infrared channel grisms. We examine two of these sources, SDSS J1723+3411 and
SDSS J2340+2947, using HST WFC3/IR grism data and supporting
spatially-unresolved spectroscopy from several ground-based instruments to
explore the size of spatial variations in observed strong emission line ratios
like O32, R23, which are sensitive to ionization parameter and metallicity, and
the Balmer decrement as an indicator of reddening. We find significant spatial
variation in the reddening and the reddening-corrected O32 and R23 values which
correspond to spreads of a few tenths of a dex in ionization parameter and
metallicity. We also find clear evidence of a negative radial gradient in star
formation in SDSS J2340+2947 and tentative evidence of one in SDSS J1723+3411,
though its star formation is quite asymmetric. Finally, we find that reddening
can vary enough spatially to make spatially-resolved reddening corrections
necessary in order to characterize gradients in line ratios and the physical
conditions inferred from them, necessitating the use of space-based IFUs for
future work on larger, more statistically robust samples.
