Fig. 11. Numerical results for the phototactic response.

(a) The reorientation trajectories of three wavy swimmers are shown for µs₀ = 0.5 (corresponding to s₀ ≈ 0.3 lux). They are initially swimming away from the light source and then turn around after the light is switched on from the left when colonies are at the origin (yellow star). (b) Evolution of ϕ as a function of time for the same swimmers. Light is turned on at t = 0. The thin black dashed, dash-dotted, and dotted lines are the respective fits using Eq. (16), with τ = 4.5 ± 0.1 s, τ = 4.0 ± 0.1 s, and τ = 3.9 ± 0.1 s. Curves are also adjusted with the amplitude parameter π/ 2 − ζ to account for the noise in the swimming direction, respectively 0.99, 0.93, and 0.83 for ξ = 0.05, 0.2, and 0.5.