Title: Molecular spectroscopy in local and high-redshift galaxies: What do “dense gas tracers” mean?
Speaker: 西村優里（天文学教室）／Yuri Nishimura (Department of Astronomy, The University of Tokyo)
Thanks to the technical advancement of (sub)millimeter observing facilities, a great number of molecular lines are now routinely observed with high sensitivity and high angular resolution. These molecular lines and line ratios are useful tools for studying physical, kinematic, and chemical properties of extragalactic systems. To fully exploit line diagnostics, it is important to relate different size scale observations: detailed understanding of nearby systems by spatially-resolved observations is essential to better interpretation of more distant objects which cannot be observed at the same physical resolution.
In this talk, I will present (1) 10 pc-scale multiline mapping toward a Galactic star-forming region W3(OH); (2) spatially- and spectrally-resolved HCN and HCO+ observations of local (ultra)luminous infrared galaxies from the CONquest sample (for more detail on CONquest, see Falstad+2021); and (3) ALMA Band 3 (rest-frame ~350 GHz) line survey toward the Cloverleaf, a gravitationally-lensed quasar at z=2.56. I will first discuss which molecular emission arises from which part of the molecular cloud, and then focus on how galactic-scale dynamics, such as outflows, can alter line ratios.
Title: Evaluation of magnitudes of the Starlink satellites by simultaneous multicolor observations
Speaker: 堀内貴史（天文センター）／ Takashi Horiuchi（Institute of Astronomy, The University of Tokyo)
The U.S. company, SpaceX plans to launch 42,000 Starlink satellites by the mid-2020s. However, these satellites orbit at relatively low altitudes (e.g. 550 km), and there are concerns that the light pollution from sunlight reflection likely affects observations. In January 2020, SpaceX launched a test satellite, Darksat with a black coating on its surface to reduce the reflection flux. In order to verify the effect of its black coating, we observed Darksat and unpainted Starlink satellites by simultaneous multicolor observations (g’: green, Rc: red, and Ic:near-infrared) with the 105 cm Murikabushi telescope/MITSuME. While the magnitude of Darksat is about 7, being difficult to see with the naked eyes, this brightness is sufficient to affect any observations. In June 2020, SpaceX launched Visorsat, which is a satellite with a sun visor to reduce the reflected sunlight. At the present stage, there is no sufficient verification on whether the sun visor is effective at various wavelengths. In this study, we are therefore conducting the simultaneous multicolor observations of Visorsat and the ordinary Starlink satellites through the OISTER campaign. The preliminary observations of Visorsat with the Murikabushi telescope have already shown that the apparent magnitude of Visorsat is not fainter than that of Darksat, ranging from 6.5 mag (g’ band) to 5.7 mag (Ic band). Since most of the satellites to be launched by SpaceX in the future will be visor satellites, it is very important to investigate the effects of the Starlink satellites as soon as possible to reduce the light pollution in astronomical observations.
Title: Cosmic-ray Acceleration & Escape from Intermediate-Aged Supernova Remnant Kes 79
Speaker: Paul K. H. Yeung（Department of Physics, The University of Tokyo)
Hadronic γ-ray sources of supernova remnant — molecular cloud (SNR–MC) interactions can serve as stopwatches for the escape of cosmic rays (CRs) from SNRs, which gradually develops from highest-energy particles to lowest-energy particles with time. Recent multiwavelength studies confirmed the interaction of the intermediate-aged SNR Kes 79 with molecular clouds. In this work, we analyze the 11.5 yr Fermi-LAT data to investigate the γ-ray feature in/around the Kes 79 region. With ≥5 GeV data, we detect two extended sources: Src-N (the brighter one; radius ≈0.31°) concentrated at the north of the SNR while enclosing a powerful pulsar — PSR J1853+0056, and Src-S (radius ≈0.58°) concentrated at the south of the SNR. Their spectra have distinct peak energies (≈1.0 GeV for Src-N and ≲0.5 GeV for Src-S), suggesting different origins for them. In our hadronic model that includes the leaked cosmic rays (CRs) from the shock-cloud collision, even with extreme values of parameters, SNR Kes 79 can by no means provide enough CRs reaching clouds at Src-N to explain the
local GeV spectrum. We propose that the Src-N emission could be predominantly reproduced by a putative pulsar wind nebula powered by PSR J1853+0056. On the other hand, our same hadronic model can reproduce a majority of the GeV emission at Src-S with typical values of parameters. Also, SNR Kes 79’s relatively softer γ-ray spectrum peaked at a relatively lower energy is in agreement with its intermediate age, based on the modelled evolution of cosmic-ray escape from an SNR.
Title: Environment and AGN activity of distant quiescent galaxies revealed by multi-wavelength surveys in the COSMOS field
Speaker: 伊藤 慧 (天文学専攻) /Kei Ito（Department of Astronomy, The University of Tokyo)
Recent multi-band observations have found that galaxies with suppressed star formation activity exist even in the high redshift universe. The state-of-art spectrograph has now confirmed them up to z~4. On the other hand, it is not well understood why they get quenched at such a high redshift, even though the cold streams are expected to supply gas. One of the preferable quenching mechanisms is the feedback from active galactic nuclei (AGNs). In addition, it has been challenging to see how quenching is connected to their living environment inside the large-scale structure of the distant universe. The cosmic evolution survey (COSMOS) is one of the preferable datasets to reveal these points since it has both a large survey area and deep multi-band photometry. In this talk, I will introduce our recent two papers on quiescent galaxies at high redshift. The first explores the spatial distribution differences among massive quiescent galaxies, mass star-forming galaxies, and Lyα emitters at 2<z<4.5. The second conducts a stacking analysis of X-ray and radio images for massive quiescent galaxies up to z~5 to explore the contribution of AGNs to quenching.
Title: NASA Astrophysics: From the past to the future
Speaker: Dr. Paul Hertz (NASA Astrophysics Division Director)
Venue: 東京大学本郷キャンパス 理学部化学本館５階講堂
Dr. Paul Hertz, the director of the Astrophysics Division in the Science Mission Directorate at NASA is visiting Japan. A special seminar by Dr. Paul Hertz is scheduled on this Thursday 7 July from 3:00pm at Hongo campus of University of Tokyo. We are now just in front of the entrance of the new world explored by the James Web Space Telescope, whose first light image is going to be public on 12 July. Dr. Paul Hertz gives us a talk on NASA’s astronomy and astrophysics researches including the future perspective of science missions. We would welcome participation of students and young scientists in wide research areas including not just astronomy, physics, earth and planetary science but also other science fields
Title: Imaging of the Supermassive Black Hole in Our Galaxy, Sgr A* with the Event Horizon Telescope
Speaker: 小藤由太郎 (天文学専攻) /Yutaro Kofuji（Department of Astronomy, The University of Tokyo)
The first event horizon scale image of the supermassive black hole in our Galaxy, Sgr A* was captured by the Event Horizon Telescope(EHT) Collaboration. EHT is the Very Long Baseline Interferometry (VLBI) that links radio dishes around the world to create an Earth-sized telescope virtually. High-resolution observations of EHT enable us to see the vicinity of the black hole. We analyzed the reconstructed images and concluded that it is highly likely that Sgr A* has ~50 uas ring structure and this is consistent with the shadow of the Kerr black hole which weighs ~4 million solar masses. In this seminar, I would like to summarize the major results, then explain the details of our imaging process and briefly introduce the theoretical interpretations of our images.
Title: Resolving Polar Dust in AGN with JWST: Going Beyond the PSF
Speaker: Mason Leist (University of Texas San Antonio)
The launch of the James Webb Space Telescope (JWST) promises to revolutionize infrared astronomy and our understanding of inflows and outflows in active galactic nuclei (AGN). David Rosario (Newcastle University, U.K.) has been awarded JWST science time to explore and characterize diffuse polar dust emission found in AGN using JWST Mid-infrared Instrument (MIRI) imaging. The Galactic Activity, Torus and Outflow Survey (GATOS2) collaboration will have access to these data, of which I am a member. Thanks to JWST’s exquisite low surface brightness sensitivity in the mid-infrared (MIR; 5-25 μm) observations of the diffuse polar dust emission found in AGN will be enabled unprecedented sensitivity. Relying on JWST’s stable PSF, we plan to use deconvolution to establish the structure of this diffuse emission below the resolution of the telescope. We will explore five different deconvolution techniques and select the best method based on comparisons of the flux conservation, FWHM, and Strehl ratios of the deconvolved images with an input model. To explore each technique, we have used the MIRI simulation software (MIRISim) to simulate JWST’s complex PSF convolved with a toy model of an AGN consisting of a resolved bicone and an unresolved AGN point source. Here I discuss the preliminary results on our assessment of the optimum deconvolution strategy.
Title: High-mass star formation in the early universe and their analogous observational signatures in the present-day universe
Speaker: 細川隆史（京都大学）/ Takashi Hosokawa (Kyoto University)
Title: Chemical abundances of time-series spectra of Classical Cepheids with WINERED
Speaker: Scarlet Elgueta（Department of Astronomy, The University of Tokyo)
Classical Cepheids have been proved to be multipurpose, their use is not only limited to precise distance determinations, they are indeed excellent chemical tracers, as their spectra exhibit a large number of absorption lines of various kinds of elements. Moreover, the analysis of the spectra collected with the high-resolution near-infrared spectrograph WINERED in the YJ bands has revealed the presence of a robust number of newly identified absorption lines corresponding to Fe-peak, alpha-enhanced, heavy metallic, and biogenic elements.
In this talk, I plan to review the method applied in my doctoral thesis that led to precise and accurate estimates of fundamental stellar parameters of our sample of Cepheids, which, in tandem, led to abundance estimates that are in perfect agreement with the results of long history optical studies. In this way, we prove the capabilities of the unexplored YJ bands to unveil exotic regions within our galaxy, and therefore, pave the way to provide more insights into galactic archaeology through the study of different phenomena, such as the metallicity gradient of our galaxy, as well as the abundance estimates of n-capture elements. And I’d also like to take the chance to discuss future plans related to WINERED observations in Chile.