Correlation between log B and log n_H in ρ Oph-A. Small circles represent B strength estimated with the DCF method at band D. Small circles in blue further represent data within the region where Stokes-I ≥ 0.4 Jy/arcsec², corresponding to the densities log n_H ≥ 5.2. The bigger circles in green represent median values of B binned in each interval of log n_H of ~0.08 (see texts). Mean values of B estimated with ADF (red triangles), DMA (blue diamonds), and ST (orange squares) methods toward subregion (a) and (e) are overplotted. The solid green line represents the median value log B ≈ 2.81 at low densities. The solid blue line shows the power-law fit toward the binned data of B using the DCF method toward more denser region (covered by the orange shaded box), resulting k = 0.47 ± 0.18. The black dash-dotted line indicates the critical power-law $B\propto n_{\mathrm{H}}^{0.5}$ for strong B-fields, predicted from the theoretical models (Mouschovias & Ciolek 1999). The black dashed line indicates the relation found by Crutcher et al. (2010) using the Zeeman observational data.