投稿者: writer

August 28 Wed 14:30-15:30
ALMA-J Seminar
hybrid; Room 102 in ALMA Building and Zoom

詳細は下記からご覧ください。

=============== August 28 Wed===============

Seminar: ALMA-J Seminar
Date and time: August 28th, 2024 (Wed.), 14:30-15:30 JST
Place: ALMA Building Room 102 / Zoom (hybrid)

Speaker : BORIS S. KALITA (Joint-Kavli Astrophysics Fellow – Kavli-IPMU, Japan | KIAA, China)
Title : The formation and influence of star-forming clumps in high redshift galaxies

Clumps have been found to dominate star formation in gas-rich (z > 1) galaxies,
thereby driving their overall evolution. I will discuss recent results from a
collection of works on this topic, that utilize public data from the James Webb
Space Telescope (JWST) and the Atacama Large Millimeter Array (ALMA) to understand
the role of clumps in galaxy evolution during the latter phase of the Cosmic
Noon (z = 1 – 2).

1. Clumps can now be detected and studied across rest-frame UV to near-IR wavelengths.
   Therefore, we conduct a stellar-mass tracing morphological analysis of the host galaxies.
2. We observe a clear evolution of galaxies from being clumpy to bulge-dominated,
   revealing how galaxy morphologies and their substructures evolve over cosmic time.
3. We estimate a clump mass-size relation along with a stellar mass function,
   finding them to match the theoretical expectations for clumps forming due to
   instability-driven coherent collapse. Thus, we observationally verify the disk
   instability formation scenario even for the most massive of these structures.
4. Our measurements (and predictions) are consistent with the properties of clumps
   in z > 1 lensed systems, bridging the long-standing gap between lensed and unlensed
   studies. Thus, we build a coherent picture of clump formation across various
   observational scales.
5. We establish the clear coexistence of spiral arms and star-forming clumps,
   which is important for understanding the dynamical stability of the gaseous and
   stellar components of galaxies.

Organizers : Kshitiz Mallick, Yuichi Matsuda

August 21 Wed 14:30-15:30
ALMA-J Seminar
hybrid; Room 102 in ALMA Building and Zoom

詳細は下記からご覧ください。

=============== August 21 Wed===============

Seminar: ALMA-J Seminar
Date and time: August 21st, 2024 (Wed.), 14:30-15:30 JST
Place: ALMA Building Room 102 / Zoom (hybrid)

Speaker: Satoko Takahashi (NAOJ ALMA Project / SOKENDAI)
Title: An extremely Young Protostellar Core, MMS1/OMC-3: Episodic mass ejection history traced by the micro SiO jet.

High-angular resolution and high sensitivity achieved with ALMA enabled us to detect candidates of extremely young protostellar sources, which are not detected even at 70um while exhibit very compact / young molecular jet (~1000 au / ~100 yr). They are considered to be in a phase right after the protostar formation and show the first mass ejection history. In this talk, I present ~0.2 arcsec resolution observations of the CO (2–1) and SiO (5–4) lines made with the ALMA toward an extremely young intermediate-mass protostellar source, MMS 1 located in the Orion Molecular Cloud-3 region. We have successfully imaged a very compact CO molecular outflow (~2000 au) and a collimated SiO jet (< 1000 au). The maximum jet speed is estimated to be as high as 93 km/s. The SiO jet wiggles and displays a chain of knots. These are the first direct evidences that MMS 1 already hosts a protostar. The position-velocity (PV) diagram shows two distinct structures: (i) bow-shocks associated with the tips of the outflow, and (ii) a collimated jet, showing the jet velocities linearly increasing with the distance from the driving source. Comparisons between the observations and numerical simulations quantitatively share similarities such as multiple-mass ejection events within the jet and Hubble-like flow associated with each mass ejection event. Finally, our ALMA jet study was compared with a submillimeter flux variability study performed with JCMT/SCUBA2. While there is a weak flux decline seen in the 850um light curve obtained with JCMT/SCUBA2 toward MMS1, no dramatic flux change events are detected. This suggests that there has not been a clear burst event associated with the mass accretion onto the protostar within the last 8 years.

Organizers : Kshitiz Mallick, Yuichi Matsuda

August 7 Wed 14:30-15:30
ALMA-J Seminar
hybrid; Room 102 in ALMA Building and Zoom

詳細は下記からご覧ください。

=============== August 7 Wed===============

Seminar: ALMA-J Seminar
Date and time: August 7th, 2024 (Wed.), 14:30-15:30 JST
Place: ALMA Building Room 102 / Zoom (hybrid)

Speaker: Qi-Ning Hsu
Affiliation: National Tsing Hua University
Title: Submillimeter Extragalactic Background Light and Galaxy Number Counts

Abstract:
The extragalactic background light (EBL) is the cumulative radiation from beyond
our Milky Way galaxy and is essential for understanding cosmic history. However,
the origin of the EBL at submillimeter wavelengths, particularly near the peak
of the cosmic infrared background, remains uncertain. To investigate this, we
conducted galaxy number counts to determine the origin of the 450 micron EBL
using SCUBA-2 observations in 10 massive galaxy cluster fields. The strong
gravitational lensing provided by these clusters allows us to construct
ultra-deep number counts, over ten times deeper than those obtained from blank
fields. By carefully accounting for possible systematics, we achieved significant
counts down to ~0.1 mJy. Comparing our measurements to those made by the COBE
satellite, we found that at the sub-mJy level, the 450 micron EBL is entirely
resolved. Thus, we present the first evidence that discrete sources, likely of
extragalactic origin, fully contribute to the 450 micron EBL, with about half
of it originating from sources with sub-mJy flux densities. In this talk, I will
introduce the submillimeter EBL, describe how we conduct galaxy number counts in
the submillimeter regime, and present my recent works.

Organizers : Kshitiz Mallick, Yuichi Matsuda