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#author("2026-04-15T01:30:19+00:00","default:wwwadm","wwwadm") #author("2026-04-15T01:42:57+00:00","default:wwwadm","wwwadm") [[IoA_Seminar]] #contents * 講演リスト [#w4d60d77] ** No. 441 : May. 28, 2026 (Thu) 15:30-16:30 [#dad05fe7] *** Place: Lecture room, Institute of Astronomy, University of Tokyo /Zoom (hybrid) [#va7fc746] *** Speaker: James Jackson (NRAO, USA) [#d2a6b465] *** Title: [C II] and [O I] Absorption and Self-Absorption from the “Skins” of Clouds [#kf065e92] Language: 英語 (English) Abstract: At high spectral resolution, the [C II] 158 mm and [O I] 63 mm lines exhibit ubiquitous absorption and self-absorption features that are difficult to reconcile with emission arising solely from photodissociation regions associated with OB star clusters. We instead propose that these features originate in the photodissociated “skins” of molecular clouds externally illuminated by the ambient interstellar radiation field (ISRF). Meudon PDR models show that a standard Habing field produces surface layers with moderate optical depths in [C II] (τ ~ 0.5) and larger optical depths in [O I] (τ ~ 2–5), along with subthermal excitation temperatures (Tₑₓ ~ 10–20 K). Under these conditions, the surface layers naturally produce absorption against bright continuum sources and self-absorption against bright line emission. Detailed modeling of the Nessie A cloud reproduces the observed line profiles well. An examination of the HYGAL SOFIA survey toward 25 bright continuum sources shows that these features are common, including absorption or self-absorption at the systemic velocity of the star-forming cloud, multiple absorption components from foreground clouds at distinct velocities, and systematically stronger absorption in [O I] than in [C II]. Because all clouds are exposed to the ISRF, this mechanism is likely widespread. In extragalactic observations, coarse spectral resolution can wash out these absorption features, leading to a significant underestimate of the intrinsic [C II] and [O I] line emission. ** No. 440 : Apr. 16, 2026 (Thu) 15:00-16:00 [#dad05fe7] *** Place: Room 1109, Department of Astronomy, University of Tokyo /Zoom (hybrid) [#va7fc746] *** Speaker: Joss Bland-Hawthorn (Director, Sydney Institute for Astronomy, U Sydney) [#d2a6b465] *** Title: The long-term evolution of turbulent discs in high-redshift galaxies [#kf065e92] Language: 英語 (English) Abstract: Most disc galaxies go through an early epoch of being "gas rich," an era that is being actively explored today through ALMA and JWST observations. This high gas-fraction phase got going much sooner (z > 3) than anticipated by cosmological N-body simulations. A new class of controlled (Nexus) simulations of these early times reveals that these turbulent discs have extraordinary properties. Unexpectedly, m=2,3 spiral arms, stellar and gaseous bars, even X-shaped/peanut bulges, all form under these conditions. The high gas content accelerates stellar migration and stabilizes the disc against buckling. Moreover, baryon sloshing driven by strong feedback gives rise to thick stellar discs, a likely origin of alpha-enriched thick stellar discs observed today. The sloshing gives rise to specific signatures that may already be observable in ALMA data. We discuss the implications of the new work on galaxy studies. ** No. 439 : Apr. 14, 2026 (Tue) 16:15-17:15 [#dad05fe7] *** Place: Room 1109, Department of Astronomy, University of Tokyo /Zoom (hybrid) [#va7fc746] *** Speaker: Donald Figer (Rochester Institute of Technology, USA) [#d2a6b465] *** Title: Photon Counting CMOS Imaging Detectors for Optical and UV Astrophysics [#kf065e92] Language: 英語 (English) Abstract: NASA’s Habitable World Observatory (HWO) will observe faint sources in ultralow (photon-per-hour) backgrounds. In this talk, we present NASA-funded research to advance single-photon counting and radiation-tolerant CMOS detectors for NASA missions, in particular, those requiring optical/UV photon counting detectors. In the project, we will measure the performance of Fairchild Imaging large-format single photon counting and photon number resolving CMOS imaging detectors (HWK4123) before and after radiation that simulates the environment at L2. These detectors have very low capacitance sense nodes to produce a large voltage response to a single photon. In a predecessor project, we found that performance for a similar detector (QIS, Gigajot Technologies) is little-changed after exposure to 50 krad(Si). The dark current can be set to beginning-of-life levels with modest additional cooling, 4–6 K for an 11-year mission. The project seeks to minimize the transient and long-term effects of radiation in NASA missions and also to design a single photon counting and photon number resolving NIR detector with similar architecture.
