第1783回 天文学教室談話会

2024年4月23日(火) 16:15-17:15

Title: Circumgalactic medium around Lyman alpha emitters probed with deep narrowband images
Speaker: Satoshi Kikuta 菊田智史 (Department of Astronomy 天文学教室)
Language: Japanese

The circumgalactic medium (CGM) is a source for a galaxy’s star-forming fuel, the venue for galactic feedback and recycling, and thought to play an important role in galaxy evolution. To characterize the CGM around forming galaxies, we conducted deep imaging observations of Lyα emitters (LAEs), low-mass star-forming galaxies, with the Hyper Suprime-Cam on the Subaru Telescope to detect diffuse Lyα emission from their CGM, or Lyα halos (LAHs) using a narrowband filter which can capture Lyα emission from z = 2.84. The depth of our data, together with the wide-field coverage including a protocluster, enable us to study the dependence of the shape of LAHs on various properties, including Mpc scale environments. UV and Lyα images of 3490 LAEs are extracted, and stacking the images yields surface brightness sensitivity of ~1e-20 erg/s/cm^2/arcsec^2 in Lyα. Dividing the sample according to their photometric properties, we find that LAEs in the central regions of protoclusters appear to have very large LAHs. This could be caused by combined effects of source overlapping and diffuse Lyα emission from cool intergalactic gas permeating the forming protocluster core irradiated by active members. For the first time, we identify “UV halos” around bright LAEs that are probably due to a few lower-mass satellite galaxies. Through comparison with recent numerical simulations, we conclude that, while scattered Lyα photons from the host galaxies are dominant origin for LAHs, star formation in satellites evidently contributes to LAHs, and that fluorescent Lyα emission may be boosted within protocluster cores at cosmic noon and/or near bright QSOs. We would also like to report on Lyα surface brightness profiles of LAEs during the pre- and post-reionization epochs (at z=5.7 and 6.6) using a catalog of LAEs obtained from narrowband data of the recently conducted HSC-SSP survey.

今後の予定

• 2024年4月30日(火) 16:15-17:15 — Frantisek Dinnbier (天文学教室)
• 2024年5月14日(火) 16:15-17:15 — 澤田涼(東大宇宙線研究所)
• 2024年5月21日(火) 16:15-17:15 — 原田ななせ(国立天文台)
• 2024年5月28日(火) 16:15-17:15 — 霜田治朗(東大宇宙線研究所)
• 2024年6月11日(火) 16:15-17:15 — 市川幸平(早稲田大学)

今年度終了済みの談話会

  第1781回 天文学教室談話会

2024年4月9日(火) 15:00-16:00

Title: Search for phosphine in prestellar cores
Speaker: Kenji Furuya 古家健次 (Department of Astronomy 天文学教室)
Language: English
Understanding in which chemical forms phosphorous exists in star- and planet-forming regions and how phosphorus is delivered to planets are of great interest in terms of the origin of life on Earth. Phosphine (PH3) is considered an important species for understanding phosphorus chemistry, but has never been detected in star- and planet-forming regions.
In this talk, I will present our recent observational and theoretical studies on PH3 in prestellar cores. We performed sensitive observations of PH3 toward low-mass prestellar core L1544 with the ACA stand-alone mode of ALMA. While the line was not detected, the non-detection provides the upper limit to the gas-phase PH3 abundance in L1544. Based on our gas-ice astrochemical modeling, we find the scaling relationship between the gas-phase PH3 abundance and the volatile (gas and ice with larger volatility than water) P elemental abundance for given physical conditions. This characteristic and well-constrained physical properties of L1544 allow us to constrain the upper limit to the volatile P elemental abundance, which is a factor of 60 lower than the overall P abundance in the ISM. Then the majority of P should exist in refractory forms. The volatile P elemental abundance of L1544 is smaller than that in the coma of comet 67P/C-G, implying that the conversion of refractory phosphorous to volatile phosphorous could have occurred along the trail from the presolar core to the protosolar disk through e.g., sputtering by accretion/outflow shocks.

  第1782回 天文学教室談話会

2024年4月16日(火) 16:15-17:15

Title: Dust Dynamics and Growth during Star and Disk Formation Using Non-ideal MHD Simulation with Lagrangian Particles
Speaker: Naoto Harada 原田直人 (Department of Astronomy 天文学教室)
Language: Japanese

The first step in planet formation is the collisional growth of dust grains in circumstellar disks. Recent observations suggest the existence of grown dust in protostellar systems during the early stages of star formation. Therefore, it is necessary to understand the star, disk, and planet formation processes in a unified way. For this purpose, we have developed a new numerical simulation code to simultaneously calculate the gas dynamics, the dust dynamics, and the dust growth process. A two-dimensional axisymmetric non-ideal magnetohydrodynamic simulation is performed to compute the process of protostar and disk formation from the gravitational collapse of a molecular cloud core. We also compute the evolution of the dust grains using a Lagrangian formulation, which allows us to track the trajectory and size history of individual dust particles. In this study, we calculated the gas and dust evolution from the formation of the protostar to 1 × 10^4 yr later. While particles in the envelope grew less, particles in the disk grew rapidly to centimeter sizes within the limits of our calculations. Individual particles followed a similar size history after falling into the disk; the small dust grew exponentially, and the growth curve of the large grains became quadratic. The protostellar system is filled with grown dust in the early stage and may have been prepared for planet formation. In addition, in this calculation, large grains were not lifted by the outflow and transported into the envelope, because the launching point of the outflow is slightly away from the disk. This may lead to the diversity of the dust opacity spectral index observed in the envelopes of Class 0/I sources.

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