2nd Blog Post: Interpreting CLOUDY Simulation Data

The second week of the internship went a lot smoother than the first, after becoming accustomed to using new software and getting to know the team better. After reading a few papers on emission line ratio studies of galaxies, things in the CLOUDY project don’t seem so cloudy anymore.

Using data from the 2015 CR7 discovery paper by David Sobral and his team, we apply constraints on the simulation data to determine the physical properties of CR7. This is done by looking at two emission line ratios: HeII/OIII and HeII/CIII. From the CLOUDY simulation data, we obtain a range of values for the physical conditions of CR7 including temperature, density and metallicity of the gas clouds relative to the solar metallicity.

Results from the Blackbody Model. Temperature is shown in Kelvin, along with other parameters. Parameters worth noting are temperature, and the metal line ratios; carbon-oxygen (C/O) and oxygen-hydrogen (O/H). SD stands for standard deviation.

Halfway through the week, a more complete CLOUDY simulation using the BPASS model was completed by Lara Alegre, another student studying the CLOUDY models in detail. We create a BPT diagram (devised by Baldwin, Phillips & Terlevich to discern different types of ionization sources) for the new simulated data.

BPT diagram for the new CLOUDY simulation data. The two curves shown are the criteria proposed by Kauffmann (dotted line) and Kewley (solid line) to discern between star-forming galaxies (SFGs) and active galactic nuclei (AGN). AGN sources would sit in the region above the curves. The red dots represent sources that have HeII/OIII and HeII/CIII ratios which fit the constraints set in the CR7 discovery paper.

From the BPT diagram, all sources simulated by CLOUDY lie in the region below the BPT demarcation curve, indicating none of them are AGN-like sources. All CR7-like sources are well below the curve, suggesting that CR7 is not powered by AGNs. Using the new data, we can also find further constraints on the physical conditions within CR7.

Results from the Blackbody model, using the new BPASS model data to further constrain CR7 parameters.

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