American Fulbright Student, David Vizgan, who received a Fulbright grant to study at the Technical University of Denmark, just had his first article accepted for publication in The Astrophysical Journal.

David has spent the past 7 months with the Cosmic Dawn Center at the Technical University of Denmark on investigating molecular gas tracers across the Epoch of Reionization. During his stay, he has worked on a special project which he elaborated on when we talked to him. Here is what he had to say:

“The crux of my research here at the Cosmic Dawn Center (DAWN) in Copenhagen attempts to answer questions related to the youngest, most distant galaxies in the universe. Thanks to tools like the James Webb Space Telescope, humanity will soon observe galaxies that are both farther and, hence, younger than anything we’ve ever seen in history. These galaxies lie at what we call “cosmic dawn” because they are some of the first emitters of light in the universe after its “dark ages”. Sadly, because of the vast light travel times (> 12 billion lightyears) between us and these galaxies, the only property we can really measure is the light emitted from them, and so my research investigates how to derive physical quantities — specifically the mass of hydrogen gas — from the luminosity of these galaxies.”

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David is spending 10 months at DAWN at DTU after his graduation from Wesleyan University.

“We conducted this investigation in a suite of over 11,000 simulated galaxies at a redshift of 6, which corresponds to galaxies whose light has travelled across about 12.7 billion light-years. The benefit of using simulations is that you can obtain a very large sample of galaxies across a wide range of masses and luminosities which is unobtainable through observational data alone, simply because we haven’t observed nearly as many galaxies (yet!) at such faraway distances. Our simulated galaxies are in strong agreement, in terms of their physical properties, with normal star-forming galaxies within the high-redshift universe. We find that in these galaxies, we can use the fine structure line of ionized carbon ([CII] 158 um) to obtain the molecular hydrogen mass of these far-away galaxies. Our results are in very strong agreement with recent, similar work conducted on samples of observed high-redshift galaxies. This is extremely important because molecular hydrogen is basically invisible to telescopes, but serves as the fuel for star formation; for future observations of galaxies at a redshift of 6 or more — which are easily achievable with the James Webb Space Telescope — our work demonstrates that [CII] line emission can be used to estimate these galaxies’ molecular gas budget. This work could eventually help astrophysicists answer greater questions about the star formation timescale of the universe as a whole, or play a role in completing our understanding of the history of galaxy evolution from the Big Bang until today.

I began this research in June 2019, as an inaugural member of the NSF DAWN-IRES Scholar Program in Copenhagen, which means that I’ve worked on this project with Professor Thomas Greve for almost three years. When I started this project, I had almost no research experience in astrophysics. It was this project that compelled me to attempt a return to Copenhagen, which is why I decided to apply for a Fulbright grant in the first place. In addition to being a fantastic advisor, Thomas has mentored me to develop my research skills and scientific independence, and I’m confident that I will be collaborating on research with Thomas for many years to come.”

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To the left is a plot from the paper.

The paper will be published in The Astrophysical Journal later this year.

“Since June 2019, I’ve worked on this project in bits and pieces; however, because of schoolwork, other research opportunities, and my lack of research experience, it was often difficult to find time for this research project. Therefore, I spent the first two months of my time in Denmark focusing entirely on wrapping this project up. We submitted this project in October, and last week it was accepted for publication in The Astrophysical Journal.

It really helped that many of this project’s coauthors are working in the same building as me, or attend the same meetings as me. August and September were especially useful for this research, since I had some highly productive conversations with the other coauthors in Denmark about the scope and utility of my research. These conversations eventually helped me start another project with the same dataset, which will try to trace atomic hydrogen (HI) gas with [CII] instead of molecular hydrogen. I’m also hoping to complete and submit this research to a journal before I leave Denmark in June. I believe that my research projects which I’m starting and finishing via my Fulbright grant will be the first of many in collaboration with DAWN, and I’m especially excited for the future of astrophysics in Denmark!”

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