California HI Width
By Elijah Bernstein-Cooper, August 18, 2015, 0 comments.

## HI Spectra

Up until now, I have been showing incorrect median spectra for each cloud. I was including only a portion of the pixels I should have included to calculate the median spectra. Both the HI and CO spectra were calculated incorrectly. However the correction does not affect the HI range selected. Below are the corrected spectra.

Perseus

Taurus

California

#### Figure 1

Median HI spectra with model fit in purple, and the HI velocity range used as the gray shaded region. The velocity widths are consistent with what was done in Imara et al. (2012). Also reassuring that we are selecting a reasonable width, is the that HI range derived from the Gaussian fitting is consistent with what we would derive from using the HI standard deviation spectrum. There are two CO components in California, so we would expect to find two peaks in the HI standard deviation, $\sigma_{\rm HI}$, spectrum – we do. We would then use an HI range between the edges of the two $\sigma_{\rm HI}$ components. This would be between about -4 km/s and 15 km/s. This HI width still omits a huge amount of HI omitted from the N(HI), leading to a large DGR.

## Reproducing Lee+12 IRIS $A_V$

In yesterday’s post I compared the MLE fit to the median $A_V$ values of the entire Lee+12 IRIS $A_V$ dataset. Below is another test of allowing an intercept in the polynomial fit to the median values of the $A_V$.

#### Figure 2

Top: scatter plot of the pixels used for the MLE, i.e. the unmasked pixels from the residual masking. Bottom: contour plot of all pixels in the map. Each plot shows three fits: 1) the MLE fit (MLE fit), fit only to the points in the masked, first plot, 2) the least squares fit to all the data in the plot, (poly scatter fit) 3) the least squares fit to the median data points in the plot (poly median fit). The MLE DGR agrees well with the median polynomial fit. However both of these relationships disagree with the Lee et al. (2012) derived DGR of 0.11 $\times 10^{20}$ cm$^{2}$ mag and intercept of 0 mag.