Gas Temperatures
By Elijah Bernstein-Cooper, November 1, 2015, 0 comments.

Table of Contents

Comparing Predicted Core Temperatures

Comparing Krumholz Temperatures

Since K+09 assumes that the dust associated with the CNM is the dominant shielding component for dust, the predicted gas density from the K+09 model is of the CNM. The most direct comparison of the predicted CNM temperature may be the spin temperatures, $T_s$, of individual components along LOS within the region.

Comparing Sternberg Temperatures

As described in section 5 of Bialy+15, K+09 assumed the HI shielding envelops are dominated by the CNM, and estimated assuming . The S+14 model includes an extra term in their $\alpha G$ parameter which accounts for the -associated dust. This extra term will lead to a lower predicted gas number density.

The number density, $n$, predicted by the S+14 model includes both atomic and molecular gas, since dust is assumed to be associated with all phases of hydrogen gas in the model. Thus the average predicted temperature, $T_H$, should include contributions from all hydrogen phases.

The best we may be able to do is compare $T_H$ with the distribution of the average LOS of sight spin temperature of sightlines within the region. Using $T_s$ as a probe of the temperatures for each component along the line of sight will bias the temperature distribution towards CNM temperatures due to the sensitivity limits.

Comparing Both Models to Observations

Figure 1 shows the cumulative distributions of the observed temperatures of all sightlines from Stanimirovic+14 within the Taurus-California-Perseus region.

We see that the spin temperatures of individual components agree well with the CNM temperature predicted by the K+09 model. However, the average spin temperature disagrees with the predicted gas temperature from the S+14 model by about a factor of 2 or 3, when we adopt our initial guess of $\phi_g = 2$.

An adjustment to the dust parameters could solve this discrepancy between observed and predicted S+14 average gas temperatures. In the S+14 model

where $T_H$ is the hydrogen temperature, $n$ is the hydrogen volume density, $phi_g$ is the dimensionless dust absorption factor, and $Z$ is the gas-phase metallicity.

would have to be reduced from 1 by a factor of 50 to reduce the $T_H$ by a factor of 2. However $\phi_g$ would only have to be reduced by a factor of 2 from 2 to show agreement between the average LOS spin temperature and the predicted average hydrogen temperature from the S+14 model.

Determining $\phi_g$ may be an integral step to comparing the predicted vs observed temperatures. Until now I have assumed = 2, the reasons outlined in this post.

Figure 1

Cumulative distributions of temperatures predicted and observed within the Taurus-California-Perseus region. Left: $\phi_g = 2$ in the S+14 model, right: $\phi_g$ = 1. The CDF of the spin temperature shows spin temperatures for individual components along the line of sight. These individual-component spin temperatures correspond to the temperatures of the CNM components, thus should be comparable with the predicted K+09 predicted $T_{CNM}$. Next is the observed average spin temperature along the line of sight. should be comparable with S+14 given that S+14 predicts the average temperature of the neutral gas along the line of sight (). The various CDFs plotted for and correspond to different simulated CDFs in a Monte Carlo simulation considering varying pressures in the neutral gas.