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Nitrogen emitters are an emerging population of galaxies whose nebular spectra show surprisingly strong emission lines from ionized nitrogen, which requires dramatically elevated gas-phase nitrogen abundance than in typical ISM of comparable metallicity. The emission is almost always associated with highly pressurized ionized gas and extremely young stellar populations, and in many examples exhibit spatial stratification of nitrogen enhancement. While the phenomenon is thought to indicate pollution by massive star ejecta, the detailed astrophysics is considered mysterious since the abundance anomaly reminds one of multiple stellar populations in globular clusters, and it has been proposed that extremely massive stellar objects forming in massive compact star clusters may be needed to explain this signature. One or two nitrogen emitters were known in the local universe, while in recent years more examples are discovered from Cosmic Noon to Cosmic Dawn with or without lensing. I will present photo-ionization modeling and infrared observations of two highly magnified nitrogen emitting systems localized to the proximity of nascent super star clusters at Cosmic Noon. Additionally, I will present extreme examples of nitrogen-loud nuclear starbursts found in the local Universe, from which photo-ionization modeling uncovers heavily CNO-processed and helium-enhanced nebulae, which may require self-enrichment by Very Massive Stars or Supermassive Stars. Combined with numerical simulation of star cluster formation, we favor an interpretation of the nitrogen emitters in terms of rapid self-enrichment by Very Massive Star winds inside the gravitational potential of massive star clusters.

BIO

Dr. Liang Dai is newly appointed a Professor of Physics at Fudan University and the Fudan Center for Astronomy and Astrophysics. He was an Assistant Professor in the Physics Department at University of California from 2020 to 2026. Before that, he was a Postdoctoral Member at the Institute for Advanced Study in Princeton. He received his PhD degree in physics at Johns Hopkins University in 2015. Dr. Dai was awarded an Alfred P. Sloan Research Fellowship in 2021 and an NASA Einstein Fellowship in 2015. Dr. Dai is primarily a theoretical astrophysicist, with a variety of research focus including strong gravitational lensing, dark matter phenomenology, extragalactic galaxy astronomy, astrophysical gravitational waves, and cosmological probes of new physics.

Host: Wei Zhu