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Title: Milliarcsecond Imaging of the Highest Redshift Quasars

Speaker: Dr. Emmanuel Momjian (NRAO)

Date&Time: 2024-04-05, 11:00 AM

Location: Science Hall B101

Talk to be delivered in English
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Abstract: In recent years, various optical surveys revealed large samples of quasars out to z >7. Studies have shown that at such high redshifts we are effectively within the Epoch of Reionization, when the first stars and massive black holes were formed. High redshift quasars provide both interesting constraints on the growth of the first supermassive black holes, and light sources with which to probe the ionization history of the Universe. While observations at radio wavelengths show that only a few of these high-z quasars are radio-loud, (sub)mm studies reveal a significant fraction (20-30%) of these most distant sources to be copious emitters of far-IR radiation with FIR luminosities > 10^12 Lsun. Very Long Baseline Interferometry, with its unprecedented resolving power, can be utilized to study the highest redshift quasars to 1) look at their physical structures at milliarcsecond resolution, 2) test for strong gravitational lensing to address the high mass values of their supermassive black holes, and 3) test, by direct imaging, whether the dominant power source at radio frequencies is an AGN or starburst, particularly in those sources that are strong FIR emitters. In this talk, I will give an overview of the Very Long Baseline Array (VLBA) and the High Sensitivity Array (HSA), and present observational results obtained on various radio-loud and radio-quiet quasars at redshifts z > 4 with the VLBA and the HSA. I will conclude the presentation by showcasing recent results on two particular objects: the most extended radio source imaged with VLBI at z~6, and the highest redshift radio-loud source known to date.