Vertical density distribution of stars vs. z at four different radii, R = 6 and 8.5 kpc in the inner Galaxy (panels a, b) and at R = 18 and 22 kpc in the outer Galaxy (panels c, d). The three curves represent the density distribution of stars in the gravitational field of stars-alone, stars plus dark matter halo, and stars plus dark matter halo plus gas cases. The addition of other gravitating components (gas and halo) increases the mid-plane stellar density value that causes the scale height to become smaller and the curve to become steeper. The constraining effect is mainly due to gas in the inner Galaxy (panels a, b); while in the outer Galaxy (panels c, d), the dark matter halo has the dominant constraining effect.