Density map of the SMC northwestern periphery, derived by adopting MSTO stars corresponding to intermediate-age (7 ≤ t ≤ 9 Gyr, left panel) and old (t ≥ 10 Gyr, right panel) stellar populations. Specifically, we selected stars within colour and magnitude ranges of 0.0 ≤ g − i ≤ 0.5 mag and 21.8 ≤ g ≤ 22.3 mag for the left panel, and 0.1 ≤ g − i ≤ 0.6 mag and 22.3 ≤ g ≤ 22.8 mag for the right panel, respectively. Each pixel has size of 3′×3′ and we applied a Gaussian Kernel Density Estimator with bandwidth = 0.1° for smoothing the plot.