The stacked H I 21 cm emission signal from the 8122 star-forming galaxies in COSMOS at z = 0.875−1.50. [A] The velocity-integrated H I 21 cm moment-0 image, where the integral is over the central velocity range [ −200, +200] km s⁻¹ of the stacked H I cube. The inset on the bottom left corner shows the FWHM of the beam of 90 kpc to which the individual galaxy subcubes were convolved before stacking. The contours are at (3, 4) × σ significance; note that there are no contours at the −3σ level. [B] The stacked H I 21 cm spectrum at a velocity resolution of 90 km s⁻¹, extracted from the location of the peak in the H I 21 cm moment-0 image in [A]. The dashed black curves show the ±1σ rms noise per 90 km s⁻¹ velocity channel.