Profile: Maryam Dehganian Pursues Degree Using Cloudy

By Julie Wrinn

Maryam Dehganian earned her undergraduate degree in physics from the University of Kashan, one of the top universities in Iran and ranked first in the country in research productivity. When it came time to pursue graduate work, however, she was attracted to the University of Kentucky for the chance to work with Cloudy, one of the world’s most-cited astrophysical computer programs.

Cloudy is the creation of UK professor Gary Ferland, who began work on it during postdoctoral research at Cambridge University in 1978 and continued developing it after joining UK as an assistant professor in 1980. The program has been open source since 1982 and is updated every other year.

“Since I was interested in computational astrophysics,” Dehghanian said, “joining the Cloudy team was a great opportunity for me.”

Dehganian is also the recipient of the MacAdam Graduate Excellence Fellowship in Physics, established by longtime UK professor Keith B. MacAdam and his wife, Phyllis A. MacAdam.

“This fellowship gave me the chance to be dedicated full time to my research,” Dehghanian said, “and therefore I was able to accomplish milestones that could not be reached otherwise. I have already published two papers, and the third one will be submitted soon. I am also at final stages of preparing a fourth paper. One of the published papers is actually a journal letter. A letter is like a paper, only it is more prestigious.”

Dehghanian uses the Cloudy code to conduct photoionization modeling for the disk-wind in active galactic nuclei (AGN) with the aim of studying its effects on the AGN feedback, broad line region (BLR) and absorbing components. The target case is NGC 5548, a type I Seyfert galaxy (z = 0.01717) that is one of the first AGNs to be extensively monitored. It is also one of the first AGN in which the variation of the  broad emission line flux was observed. It is approximately 245 million light years away, and the mass of its central black hole can be estimated based on the properties of the emission lines in the core region. It is some 65 million times the mass of the sun. Among astronomers, the accepted explanation for the active nucleus in NGC 5548 is the accretion of matter onto a supermassive black hole at the core.

This object was in an unusual state during the observations (2013 and 2014) and showed anomalous behavior that had never been seen before.

Dehghanian described her work as follows:

"In collaboration with scientists at Space Telescope Science Institute, we work on understanding the abnormal behavior of NGC5548, in which the soft X-ray continuum was heavily obscured by an obscurer. This obscurer made the emission and absorption lines go on a 'holiday' and no longer behave such as they were expected to behave. This phenomenon accounts for a paradox that the standard models cannot explain this phenomenon. NASA committed time on six space-based observatories--XMM-Newton, Swift, NuSTAR, INTEGRAL, Chandra and HST--to conduct an unprecedented observing campaign on NGC 5548. There are also six ground-based observatories that had been used to gather data from this object. The result of dedicating 12 observatories to track NGC5548 is a huge pan-spectral (IR through X-ray) data set.

"To find an explanation for what had happened, we need to predict the behavior of the black hole and the obscurer considering a lot of possible scenarios. We mainly use the data taken by Hubble Space Telescope and simulate the holiday that happened in the lines. To be able to model and predict this phenomenon, we need a tool to do numerical calculations. Cloudy is the tool that we use. We produce models of the emission and absorption lines and the obscuration and adapt Cloudy to fully model what we observed, improving the code. As a Cloudy developer, I will incorporate these improvements into next releases of the code. This will benefit other researchers in the field and future space missions as well.

"Cloudy is, in fact, a spectral synthesis code designed to simulate spectra from interstellar matter possibly exposed to an external source of radiation under a broad range of conditions. Cloudy simulates gas ranging from fully ionized to molecular. This makes it possible to predict many observed quantities by specifying only the properties of the cloud and the radiation field striking it. The code is being developed here in Lexington and is publicly available under an open source license, which has a two-year release cycle."

The MacAdam Fellowship, like other forms of graduate student support, provides crucial resources that accelerate the timeline for Dehghanian’s degree. After earning her Ph.D., she intends to continue her research as a postdoctoral scholar with the goal of obtaining a faculty position in physics. Meanwhile, her contributions to the Cloudy code will have a lasting impact.

“The developments from my research will be implemented into future releases of Cloudy,” she said.

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