ESPRESSO transmission spectrum of WASP-172 b for the wavelength range of the H-α line in the planetary rest frame. Upper panel: transmission spectrum in full resolution (in grey) and the same data binned by ×20 (in black). The data have been corrected for tellurics, cosmics, and the RM+CLV effect. The rest frame transition wavelength is marked with a dashed blue line. A Gaussian fit is shown in red. Lower panel: residuals of the Gaussian fit.