3rd Blog Post: Interpreting CLOUDY Simulation Data

The third week of the internship was a slow week for the CLOUDY project, but nonetheless progress has been made. Improving on last weeks efforts to forecast the physical conditions in CR7, work has been done to further constrain the sample of CLOUDY models that best represent CR7 .

Looking at the plot of the CLOUDY BPASS models that compares the UV emission line ratios (CIII/HeII and CIV/HeII), we find an interesting distribution that has a butterfly shape. If we look at the intensity of HeII emitted, we find that lower intensities occupy the left part of graph, while higher intensities occupy the right, as shown below.

A plot showing the UV line ratio tests for the CLOUDY BPASS models, including the HeII intensity of the sources. Red indicates higher intensities while blue indicates lower intensities. The population of sources seems to be separated by their intensities, with high intensity sources occupying the right area of the graph.

In real observations, many of the fainter (blue-green) sources would not be detected by telescopes. Hence, we can discard sources that have intensities lower than two orders of magnitude of the source with maximum intensity. In doing so, we eliminate all of the sources that appear on the left side of graph. It is also interesting to look at the metallicity of the gas clouds surrounding the remaining sources, shown below.

A plot showing the remaining models that would actually be observable. The colour scale on the right shows metallicity of gas clouds surrounding the models, in units of Solar Metallicity. It can be seen that as we move up the graph, metallicity increases, and depends strongly on the CIII/HeII ratio.

Now that we have further constraints on the BPASS models, we can combine them with the CR7 constraints. This brings down the total fraction of models that best represent CR7 to 9% of the original population. We can visualize these constraints on the BPT diagram, illustrated below.

A BPT diagram, showing the new constraints applied to the BPASS models, showing the demarcation curve for discriminating AGNs (above the curve) from SFGs (below the curve) proposed by Kauffmann and Kewley.

The BPT diagram indicates that the ionizing sources in CR7 are not powered by AGNs, instead suggesting star formation as the main source of ionization. However, the BPT diagram looks at the optical line ratios. UV line ratio tests seem to disagree with this result, instead placing the CR7 models in regions that are populated by AGNs, suggesting that AGNs are the ionizing sources in CR7. The reason for this is not yet known, and is thought to be a result of the computer modelling.

This project will be put on hold as more effort will be allocated to the HST Grism project.

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