Sensitivity map of the Hα imaging. Brighter colors correspond to a lower RMS and a higher exposure time. The inner disk within 5′ of the galaxy center is masked out. The black contour represents the 5 × 10¹⁹ cm⁻² H I column density level. The black dashed circle shows the GALEX FoV. The green star indicates the location of the fifth magnitude star HR 5128. The variation in background uncertainty is caused by the different exposure times in different areas due to the dithering pattern.