This page lists the Seminars that were given virtually on zoom in 2023. The EAO staff would like to thank all guest speakers and encourage new astronomers/instrument specialists to give virtual talks.
December 6th, 15:00 (HST)
Speaker: Ryo Ariyama
X-ray binary system comprised with a supergiant star and compact
object, which is possibly a stellar-mass black hole. It is located at
the center of the supernova remnant W50 at the distance of 5.5 kpc. A
pair of highly-collimated jets is ejected from SS433 with a speed of
0.26c, precessing with an open angle of 20° in a period of 162.5 days.
Recently, a point-like GeV gamma-ray source (Fermi J1913+0515) was
discovered at the northern radio edge of W50, at 0.4 deg (40 pc) away
from SS433. The position of Fermi J1913+0515 in the plane of the sky
does not overlap with the jet termination lobes and is well outside of
the precessing cone of the jets. Most surprisingly, a clear ~162 days
periodicity was detected in the GeV gamma-ray flux of Fermi
J1913+0515, indicating that SS433 at the center of W50 may be
responsible for the gamma-ray emission from it. An enhancement of HI
21 line emission toward Fermi J1913+0515 suggests baryonic origin of
GeV gamma rays.
To unveil the gamma-ray emission mechanism of Fermi J1913+0515, we
performed mapping observations in millimeter and submillimeter-wave
molecular lines with the Nobeyama Radio Observatory 45 m telescope and
James Clerk Maxwell Telescope. We detected an isolated molecular
cloud (CO+40.05–2.40) in the error circle of Fermi J1913+0515. The
size, velocity width, and mass of this cloud are, 3.5 pc, 4 km/s, and
6×10^3 Msun, respectively. The average CO J=3-2/J=1-0 ratio is 0.4,
average H_2 density is ~100 cm^(-3), and typical excitation
temperature is 4 K. These parameters are typical for dark clouds in
the Galactic disk, showing no signature of either heating or
compression. Based on these results, we will discuss possible
gamma-ray emission mechanism from Fermi J1913+0515/CO+40.05–2.40
November 22nd, 15:00 (HST)
Speaker: Changseok Kim
Title: No instantaneous AGN feedback: Star formation rates determined by SED analysis with JCMT/SCUBA-2 data
Abstract: Observationally it is still elusive how active galactic nucleus (AGN) feedback regulates star formation in massive galaxies despite its importance in galaxy evolution. One of the limitations is that a majority of star formation rate (SFR) indicators are contaminated by AGN radiation. To verify AGN feedback scenarios with reliable SFRs, we adopted Far-Infrared (FIR) emission by dust in the interstellar medium (ISM) as a primary SFR indicator since FIR emission from AGN is negligible. We performed multiwavelength spectral energy distribution (SED) analysis with the assistance of sub-mm data observed by SCUBA-2 camera at James Clerk Maxwell Telescope (JCMT). By dust FIR luminosity obtained from SED analysis, we determined SFRs of 52 local AGN host galaxies at z < 0.2, which were sampled by a broad range of outflow kinematics. We found that SFR based on Dn4000 break shows a significant offset compared to dust luminosity based SFR, while artificial neural network (ANN) based SFR (Ellison et al. 2016) are relatively comparable. We also found that SED analysis without AGN hot dusty torus component overestimates dust luminosity, especially by a factor of two when both FIR and sub-mm data are unavailable. Finally, specific SFR (sSFR) shows a positive correlation with AGN activity (outflow strength and Eddington ratio), suggesting that there is a lack of instantaneous quenching of star formation due to AGN feedback. This may indicate that AGN outflow requires a certain time scale to quench star formation in its host galaxy, which is called a delayed AGN feedback scenario.
November 15th, 16:00 (HST)
Speaker: CHEN, Chian-Chou (TC) Academia Sinica Institute of Astronomy and Astrophysics (ASIAA)
Title : AMUSE2 – a systematic submillimeter survey around quasars hosting Lyman-alpha nebulae at z=2-4
Abstract : Studies of protoclusters and their associated members during cosmic noon provide an excellent opportunity to understand how present day massive galaxy clusters formed and in particular how the predominantly dense environment plays a role in the formation processes. However, research on protoclusters has been hindered by small sample sizes and the use of heterogeneous data sets. To address these issues, we have been conducting a submillimeter survey around a statistical sample of ~20 bright quasars at z=2-4 that host Lyman-alpha nebulae, providing insights into the coevolution between dusty star-forming galaxies (DSFGs) and the host quasars in dense protocluster environments. In this talk, I will share the main results of this survey, in particular how prevalent the DSFGs are in these dense environments and how they trace the Mpc-scale filamentary structures. I will also present preliminary results from our ALMA follow-up observations, which allow us to confirm the membership of these DSFG candidates, as well as to study the environmental impact on their physical properties.
November 1st, 14:00 (HST)
Title: S2TDF: SCUBA-2 survey in JWST-Time Domain Field for the discovery of SMGs to reveal the hidden star formation of the universe
Speaker: Minhee Hyun (Korea Astronomy and Space Science Institute)
Abstract: Tracing the star formation history over the cosmic time is very important to understand the evolution of the universe and the galaxies. It is especially necessary to unveil the hidden star formation history of the dusty star-forming galaxies near the cosmic noon or more to draw the complete picture of the star formation scenario of the universe. For this, sub-mm galaxies (SMGs), a population of dusty and intensively star-forming populations at high-z, can be potent objects. One of the big questions about the SMGs is which physical mechanism causes their high star-forming rates. One of the potential answers is galaxy merging, but limitations in low resolution and depth make it hard to directly detect the merging features in the previous optical/NIR images of SMGs. In this study, we performed a survey for discovering sub-mm galaxies with JCMT SCUBA-2 in the JWST Time Domain Field(JWST-TDF) and for studying their physical properties with other multi-wavelength data, including JWST. JWST TDF field is ~14’ sky area in the continuous viewing zone of the JWST and is one of the deepest extragalactic surveys of the JWST Guaranteed Observation (GTO 1176, PI: R. Windhorst). The survey depth will reach the depth down to ~ 29 AB, which is enough to study the properties of SMGs in the optical/NIR regime. In this talk, we will introduce the results of the S2TDF survey with JCMT SCUBA-2 and the preliminary results from the JWST data.
October 25th, 10:00 am (HST)
Title: Interstellar Magnetic Fields: From Star Formation to Galaxy Evolution
Speaker: Kate Pattle, UCL, GB
Abstract: Recent advances in submillimetre dust emission polarimetry are revolutionizing our understanding of the magnetic fields which thread the interstellar media of the Milky Way and other galaxies. In this talk I will discuss the insights which we are gaining into the energy balance, dynamics and evolution of the magnetized interstellar medium, on size scales ranging from nearby star-forming regions to the disc and superwind of the starburst galaxy M82, from recent observations made with the POL-2 polarimeter on the JCMT. I will particularly discuss how we can infer the dynamic importance of magnetic fields from observations of magnetic field geometries in the dense interstellar medium, and the emerging evidence for how the interaction between magnetic fields, outflows and feedback may influence star formation efficiency on both small and large scales.
July 14th, 11:00 am (HST)
Title: Magnetic fields in molecular clouds and star formation
Speaker: Junhao Liu, EAO, USA
Abstract: The star formation process plays a fundamental role in the formation and evolution of galaxies, as well as in the life cycle of interstellar media. While significant progress has been made in understanding star formation, the role of magnetic fields in this process remains a topic of debate. Dust polarization observations, which capture linearly polarized emission from dust grains, provide valuable insights into the plane-of-sky magnetic field structure in both diffuse interstellar medium and dense molecular clouds. In this talk, I will provide a review of the magnetic field properties in molecular clouds and star formation, drawing from polarization observations analyzed using several widely-used statistical methods such as DCF, HRO, and KTH. Based on these observational studies, it has been found that molecular clouds typically exist in a trans-to-sub-Alfvénic and magnetically sub-critical state, with magnetic fields stronger than gravity and turbulence. Furthermore, as the density within molecular clouds increases, the gravitational force gradually dominates over magnetic fields, leading to the formation of magnetically trans-to-super-critical clumps and cores. Additionally, the star formation activities triggered by gravity can amplify non-thermal motions, resulting in some clumps and cores becoming super-Alfvénic, where magnetic fields are weaker than turbulence.
March 21st, 10:00 am (HST)
Title: Infall motion with rotation of the cluster forming clump GGD12-15
Speaker: Tomomi Shimoikura, Otsuma Women’s University, Japan
Abstract: We present results of mapping observations with various molecular lines made toward GGD12-15 using the NRO 45 m telescope and JCMT. GGD12-15 is an active star-forming site embedded in the Mon R2 molecular cloud. Previous studies revealed a molecular clump with a mass of ~1000 Mo in this region. We investigated the molecular gas kinematics in the clump. The distribution of the C18O (J=3-2) emission is similar to that of a star cluster forming therein, with an elliptical shape of ~1 pc in size. There is a massive core with a radius of 0.3 pc and a mass of 530 Mo in the center of the clump. The velocity structure of the C18O (J=3-2) emission line shows two velocity components around the core, which are prominent in a position-velocity (PV) diagram along the extended structure of the clump. A velocity gradient is also observed in a PV diagram along the direction perpendicular to the axis of the extended structure of the clump. We made a simple model of a gravitationally collapsing clump and compared it with the observed data. The results suggest that the clump is collapsing with rotation.
January 18th, 10:00 am (HST)
Title: The Commensal Radio Astronomy FAST Survey (CRAFTS) – Refreshing the View of the Milky Way
Speaker: Di Li, NAOC/CAS/FAST, China
Abstract: Inspired by the Arecibo telescope, the FAST telescope has been in operation for three years as the world’s largest single-dish antenna. In GHz bands, HI and pulsars have been two primary science targets. No major telescope, including Arecibo, Parkes, GBT, etc., has realized large-scale simultaneous survey of HI and pulsars, until FAST. Facilitated by our proprietary high-cadence-CAL technique, the CRAFTS survey records pulsars, Galactic HI, HI galaxies, and transients data streams, simultaneously. CRAFTS has covered 18% of the Northern sky, achieving 1% accuracy in HI flux calibration, discovering thousands of HI galaxies, discovering 160 new pulsars including a double-neutron-star, and 6 new FRBs. I will report here a few science highlights from CRAFTS as well as related PI programs, such as the first HI-narrow-self-absorption (HINSA) Zeeman measurement (Ching et al. 2022, Nature cover), a unified picture of the frequency evolution of FRB’s polarization (Feng et al. 2022 Science), the largest extended HI structure (Xu et al. Nature 2022), etc. I will also briefly report the current status of related JCMT programs.