I am continuing the discussion on using intercepts.
Some discussion points from Lombardi et al. 2015
“…unrelated foreground or background material can contribute to the observed PDF. One way to correct for this is to look at the lowest extinction value in a large area around the cloud and to remove this amount from the extinction map (see also Schneider et al. 2015). Of course, this is a crude approximation since the subtracted column density is taken to be constant within the field. As a result, we expect “corrected” column densities to be affected by an additional noise equal to the average scatter of the superimposed material. This quantity, however, can be estimated (although approximately) by check- ing the off-field column density scatter and by applying a set of offsets that spans the same range in extinction.”
Foreground and background likely dominate the extinction below mag, or about mag.
- The PDFs for the clouds in their sample ( Ophiucus, Perseus, Orion B, Orion A, Polaris, Pipe, California and Taurus) show truncation between mag to mag. These values are similar to those found for the transition found by theory, to mag (Sternberg et al. 2014).
Some discussion points from Planck et al. (2011).
Uncertainty in their accounts only for the measurement uncertainty, not in their uncertainty of the window used. The errors on on order of 10%. See Table 1. They assumed optically thin .
They use infrared to submm data at and GHz ( and m, respectively) from IRAS (IRIS, Miville- Deschênes & Lagache 2005) and at and GHz ( and m, respectively) from Planck (DR2 release; Planck HFI Core Team 2011b)
The IR maps have removed point sources identified from IRAS IR sources and WMAP radio sources. They masked point source pixels within 15, then interpolated from surrounding pixels to fill in the mask. See appendix D.