Surface density radial profiles of the atomic gas (left), the molecular gas (centre), and the total gas (right) from the literature compared to the profile adopted in this work (black points). The factor 1.36 for the helium correction is included. Left panel: BG78 = Burton & Gordon (1978), Wo90 = Wouterloot et al. (1990), DL90 = Dickey & Lockman (1990), BM98 = Binney & Merrifield (1998), NS03 = Nakanishi & Sofue (2003), Le06 = Levine et al. (2006), KD08 = Kalberla & Dedes (2008), and M17 = Marasco et al. (2017). Centre panel: Sa84 = Sanders et al. (1984), Da87 = Dame et al. (1987), Gr87 = Grabelsky et al. (1987), Br88 = Bronfman et al. (1988), Cl88 = Clemens et al. (1988), Di91 = Digel (1991), Lu00 = Luna et al. (2006), NS06 = Nakanishi & Sofue (2006).