IR Background
By Elijah Bernstein-Cooper, June 24, 2015, 0 comments.

I am continuing the discussion on using $A_V$ 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 ($\rho$ Ophiucus, Perseus, Orion B, Orion A, Polaris, Pipe, California and Taurus) show truncation between $A_k \sim 0.07$ mag to $0.14$ mag. These values are similar to those found for the $HI-H_2$ transition found by theory, $A_k \sim 0.04$ to $0.1$ mag (Sternberg et al. 2014).

Some discussion points from Planck et al. (2011).

• Uncertainty in their $N(HI)$ accounts only for the measurement uncertainty, not in their uncertainty of the $HI$ window used. The errors on on order of 10%. See Table 1. They assumed optically thin $HI$.

• They use infrared to submm data at $3000$ and $5000$ GHz ($100$ and $60 \mu$m, respectively) from IRAS (IRIS, Miville- Deschênes & Lagache 2005) and at $353, 545,$ and $857$GHz ($850, 550,$ and $350 \mu$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$^\prime$, then interpolated from surrounding pixels to fill in the mask. See appendix D.