Letters of Intent received in 2021

LoI 2023-2146
Cosmic Masers: Proper Motion toward the Next-Generation Large Projects

Topics

1) The Cosmic Distance Scale and the Hubble Constant
a) Megamasers
b) Rotational parallaxes
c) Local group cosmology

2) Black Hole Masses and the M-sigma Relation
a) Resolved kinematics within BH sphere of influence
b) Synergy with EHT

3) The Structure of the Milky Way
a) Structure determination from parallaxes and proper motions
b) Synergy with GAIA DR2 and EDR3

4) The Dynamics of Formation of Massive Stars
a) Dynamics of gas within 100 au of a YSO
b) Mass accretion bursts and maser flares

5) Pulsation and Outflows in Evolved Stars
a) Mass loss processes at 10s of stellar radius scale
b) Long-term evolution of evolved stars

6) Theory of Masers and Maser Sources

7) New Projects and Future Telescopes
a) Large-scale survey and monitoring programs
(JVLA, ALMA, ASKAP, MeerKAT, VLBA, EVN, EAVN, single-dishes, etc.)
b) Future projects (SKA, ng-VLA, global VLBI, regional projects)
c) Synergy with multi-frequency observations (JWST, ELT, GMT, TMT, etc.)

Rationale

Cosmic masers have been recognized since the discoveries of the first interstellar molecules of OH and H2O in 1960's. Masers are known to be widely associated with various objects, such as young stellar objects (YSO), evolved stars, in particular asymptotic giant branch stars (AGB), and active galactic nuclei (AGN). Most masers emit high brightness narrow spectral features, often over a wide velocity range from compact regions that, in the Galaxy, have sizes of order 1 au and line widths of 0.1 km/s, respectively. Thus, masers can be imaged with high spatial/spectral resolutions with radio interferometers and very long baseline interferometry (VLBI).
By utilizing these characteristics, 3-dimensional (3D) velocity fields of YSOs and AGB stars have been determined through proper motion measurements of various maser lines with VLBI. Radio astrometry has succeeded in measuring annual parallaxes of Galactic masers at distances of up to 20 kpc from the Sun. These results can be compared with the GAIA DR2 and EDR3 database to explore the Milky Way's 3D Galactic structure. An epoch-making discovery of the 22 GHz H2O maser from an AGN in 1995 provided the first definite evidence of a super-massive black hole (SMBH). It enabled to measure SMBH masses and their distances only from the geometries of the maser features. Surveys of extra-galactic mega-masers are establishing 3D structure of the local Universe and sources far enough to partake in the Hubble flow can be used to determine the Hubble Constant with an accuracy of better than 3%.
Based on the rich science addressed by maser observations and their interpretation, over the past decades, there have been IAU meetings focusing on cosmic masers spaced by roughly 5 years, and the last of these meetings was held in 2017 in Sardinia, Italy. During that meeting, more than 30 of attendees from 10 countries recognized the importance of sudden, strong brightening of masers (flare or burst), and an international collaboration network, the Maser Monitoring Organization (M2O) was organized, which has grown to 100 members by now. This new systematic pursuit of time-domain maser science has become a powerful means to investigate episodic mass accretion and ejection in YSOs, since masers are sensitive to rapid variations of physical conditions.
Following these past activities, we propose to organize the next maser symposium in Kagoshima located at the south-western part of Japan. It is the ideal place for this symposium as there is an active astronomers' group including maser sciences. In addition, Kagoshima hosts a VLBI station of VERA (VLBI Exploration of Radio Astrometry), which has been conducting maser astrometry for 20 years. Past IAU symposia on masers were hosted in the USA (1992), Brazil (2001), Australia (2007), South Africa (2012), and Italy (2017). This means that organizing the next IAUS on masers in Asia will close a gap and such symposia will have taken place in all of the world's major regions. We plan to invite researchers in relatively new communities who just have started to become engaged in observing masers with their own telescopes. They will include newly developed single-dish telescopes located in Thailand, Ghana, and other countries in Asia and Africa. Some results or plans from the newly established East Asian VLBI Network (EAVN), African VLBI Network (AVN), and global VLBI network are expected.
The year of 2023 is timely given the interval of 6 years after the last maser conference. During this period, the Atacama Large Millimeter/submillimeter Array (ALMA) has been improving its capabilities. ALMA opened new windows to observe new maser lines. More importantly, now ALMA at the highest resolution of few 10s of milli-arcseconds allows us to directly compare spatial structures of target sources with an angular resolution comparable to that of VLBI. Several large new projects will also appear within a few years. Square Kilometre Array (SKA) has just started construction this year, and pilot surveys are ongoing with its precursors such as MeerKAT and ASKAP. The next generation Very Large Array (ng-VLA) will become complementary to SKA and ALMA. Masers are proposed in these projects' white papers as important science areas. As for infrared and optical wavelengths, the James Webb Space Telescope (JWST) will be launched soon and other ground-based instruments such as Extremely Large Telescope (ELT), Giant Magellan Telescope (GMT), and Thirty Meter Telescope (TMT) are also under development. Discussion on their possible science cases and synergies will be covered in the meeting. We note that there will be APRIM meeting in August 2023 in Japan. In order to attract as many participants as possible, we will coordinate the schedule of our meeting with the LOC of the APRIM.
While the main focus of the Symposium is on cosmic masers, we intend to invite speakers from outside of the maser science and radio astronomy communities in order to broaden the impact of the Symposium through synergies with other research fields. Theoretical reviews of forefront questions of cosmic maser science are planned. Clearly, the proposed meeting will offer the opportunity to discuss advances in observation and theory and to plan challenging programs in maser research that will tackle fundamental scientific questions of the next decade in global collaboration.