Top panel: datapoints represent the position of our sample of galaxies in the V_h,max – V_rot,HI plane. The y-axis position corresponds to the rotational velocity derived from the inclination-corrected HI linewidth, V_rot,HI. The vertical errorbars represent typical y-axis errors for galaxies with V_rot,HI = 15 km s^-1 and 35 km s^-1. The x-axis position of each galaxy corresponds instead to the upper limit on the V_h,max of its host halo, inferred from the galactic kinematics measured at the outermost HI radius and assuming an NFW density profile (refer to Sect. 2.2.2). The color-coding represents the radius of the outermost velocity measurement, R_out,HI. The blue and red shaded regions represent the AM relations between V_h,max and V_rot,HI that reproduce the galactic velocity function measured in the ALFALFA survey (this work) and within the Local Volume (Klypin et al. 2015). Bottom panel: same as in the top panel, but galaxies are placed on the x-axis assuming their host halos follow the DC14 density profile. Please refer to Sect. 3 for the scientific interpretation of this figure.