NAOJ Future
Planning Symposium2021/11/09(Near) Future of Star
Formation Studies
Kengo Tomida

Astronomical InstituteTohoku University

Global Flow like
Merger, Spiral Arms,
Supernovae, etc.
Turbulence, Chemistry,
Magnetic Fields,
Irradiation, Pressure, etc.

Star/Disk Scale

Core Scale

Cloud Scale

Cosmological / Galactic Scale

Multi-Scale, Multi-Physics nature of Star Formation

Mass, Accretion,
Magnetic Fields,
Turbulence, Rotation...

Feedback:
Radiation,
Outflow / Jet,
Chemistry,
Supernovae, etc.

Outflow
Circumstellar-disk

ProtoStar
Planets

（Chabrier 2005)

Ultimate Goals ofStar Formation Studies
1. Stellar Initial Mass Function
Stellar mass determines stellar evolution.
Chemical and Dynamical feedback frommassive stars control the universe.
→ Mass distribution of stars is crucial.
⇒What is the origin of the IMF?

２. Origin of the Sun, Earth,other planets, and ourselves
Formation of our solar system isstill unclear, and now more than
4,500 exoplanets are reported.
⇒ Formation scenario of star, disk
and planets = stellar system(From Wikipedia)

Galaxy to Cloud Scale(M51, left: NASA, right: PAWS project)(MC in LMC, ALMA, Sawada et al. 2018)

Status: We are seeing internal structures and environments of star forming
regions in other galaxies with ALMA (e.g. PHANGS), JVLA, NOEMA.
Key Questions:• Where and how molecular clouds form, and how they disappear?
• What is the relation between MCs and environment (e.g. the KS law)?
• What are the conditions required for dense cluster formation / star burst?
What we need:• Complete statistics of down to small molecular clouds• Detailed kinematic and chemical information in forming MCs and ISM

Cloud to Core Scale
Status: Herschel and ALMA observations provided
detailed information about star formation in MCs.
Key questions:• What determines the structure and properties ofmolecular clouds such as turbulence, magnetic
fields, filaments (e.g. 0.1pc width), etc.?
• What controls the star formation efficiency?
• How cloud structures such as filaments
and cores relate to star formation?
What we need:• High resolution (both spatial and spectral)
information of the turbulence and magnetic
fields, as well as feedback from YSOs.
• Core and stellar initial mass functions
down to the low-mass end• Chemical diagnosis → Nomura-san(Andre et al. 2010, Herschel)Future: Galaxy-Cloud Scale• LST can play a crucial role to map molecular clouds in other galaxies aswell as structures within nearby molecular clouds including magnetic fields.
It also can enable high resolution chemical diagnosis.
(LST is complementary to interferometers like ALMA, and can cover somesciences of cancelled SPICA. Also ATT10 and Far-IR Probe in ASTRO2020?)• ALMA-2 and ngVLA will allow us to resolve detailed structures in HI andmolecular clouds in other galaxies, and provide detailed view in nearby MCs.
• Roman and PFS on Subaru can probe the low-mass end of IMF, and LST
can probe CMF.
Note: understanding the galactic
ISM (e.g. dust polarization) isvery important in the context ofcosmological foreground, too.
→ K. Tanaka et al. in prep.
Synthetic observation of gas
and B-fields in a forming MC.

(LST, Kawabe et al. 2016)

Disk Scale

L1521-F (Tokuda+)←Young

L1448 IRS3B (Tobin+)

Elias 2-27 (Perez+)

HL Tau (ALMA SV)

Evolved→

Status: ALMA, NOEMA, JVLA, particularly systematic surveys like DSHARP(Class-II) and eDisk (Class-0/I, on going), drastically changed our view.
• Disks are initially small, but massive in the early phase, and grow by accretion.
• Massive disks can fragment by gravity → binary (possibly planet) formation.
• Rich substructures like ring, gaps and spirals → signatures of planets (?)• Disk winds are rotating, carrying angular momentum away from disks.
• Polarization pattern can infer grain growth, though it is not very simple.

Disk Scale(Tobin et al. 2020,
Disk mass distribution)(Kataoka et al. 2016,
Key questions:
Polarization pattern)• What physics controls the disk structure and evolution?
• How are binaries formed, disk fragmentation vs turbulent fragmentation?
• How, where and when small grains grow into planetesimals and planets?
• What is the role of substructures in disk evolution and planet formation?
• The origin of life - how and where complex chemical species are formed?

Toward Solar System Scale
While ALMA and Subaru revealed detailed structures inprotoplanetary disks, those are way larger than the scaleof our solar system.
To approach this scale TMT, ALMA-2 and ngVLA are
crucial, and will bring us new insights on planet formation.
• Direct imaging of inner disks of ~ a few AU scales• Detection of snow lines of various species(Muto et al. 2012, HiCIAO)• Inner disks of transitional disks - how disks disappear?
Note: the innermost regions of accreting YSOs can be
optically thick to mm dust continuum.
→ ngVLA and low-frequency bands of ALMA-2.
(NB: dust opacity is highly uncertain in low frequency.)
Also, we need to find good molecular tracers to observe
kinematics in such warm/hot disks.
→ refractory species (SiO, NaCl etc.) and H2O canbe used as good tracers (Tanaka et al. 2020 →)Future: Disk-Planet Scale
ALMA-2, ngVLA as well as TMT will open
new windows to a new world.
• Systematic observations of young disks,
outflows and jets (including FHSC).
• Resolving interaction between planets and Imaging simulations of planet-disk
interaction, 100 GHz with ngVLA,
protoplanetary disks.
• Spatially resolving the solar system scale. (Ricci et al. 2018)• Broad spectral range and polarization will
provide rich information of dust properties.
• ngVLA as well as ALMA Band-1 and 2
will provide various chemical diagnosis.

Spectral index maps can trace grain
growth (Ohashi et al. ngVLA memo)(← ngVLA Project Book)

Toward the Scale of Stars
With the resolution of ngVLA, we canapproach even smaller scale of the star.
In that scale, the dynamical time scale
becomes months or even shorter.
• Photospheres of inflated massive stars→ direct comparison w/ stellar evolution• Orbital motion of tight binaries• Inner structure of the accretion flow
→ How stars gain their mass, angularmomentum and magnetic fields?
• Launching points of jets and outflows→ constraining the driving mechanism• What regulate masses of stars (starformation efficiency)? Magnetic orradiation feedback?

(K. Tanaka, ngVLA memo series)(Commerçon et al. 2021, RMHD simulation ofSF, comparing magnetic vs radiation forces)

(Machida et al. 2008,
disk fragmentation)

Binary Formation
As many stars form in binaries/multiples, binary
formation is important in various contexts but still
remains as a big mystery:• Determining IMF• Redistributing angular momentum• Stellar evolution• Planet formation

Two major processes:• Disk fragmentation by gravitational instability• Core fragmentation by turbulence
We can distinguish them using ngVLA and ALMA.
They produce different orbital separation, mass
ratio, alignment, and eccentricity distributions.
(Note: probably these are not mutually exclusive- both can work but at different scales.)(Krumholz et al. 2012,
turbulent fragmentation)

Origin of GW Sources?

(Abbot et al. 2016)

Abbot+ 2016, GW150914
Allowed Region

Note: Since they are rare, they may form in special environments
like the center of dense clusters, and we do not need to explainthem from star formation. But it is an interesting, new challenge.

>1000AU

GW150914: 36M☉+29M☉ Binary BHs(Progenitor mass is > 40M☉, favors low-metal)
The initial binary must be very tight: < ~ 1AU(c.f. RHD simulation → 40 + 30 M☉ but wide)⇒ GW + ALMA-2 / ngVLA + simulations

Krumholz et al. 2009

SF in Different Environments
IMF is considered to be universal in various
environments - but why?
There are many environmental parameters:• Metallicity (chemical composition)• Irradiation / temperature• Magnetic fields• Turbulence• Density and pressure
We are already seeing diversity/universality:
With ALMA-2, ngVLA and TMT, we will beable to observe disks and outflows in otherenvironments (which typically are far away):• low metal: LMC/SMC, outer Galaxy• high metal, dense, warm: inner Galaxy→ Constrain how environments affect SF.

(Yasui et al. 2010, disks disperse
faster in low-metal SF regions)(Tanaka et al. in prep., outflows
are universal, at least in LMC)

“High-Energy” Phenomena in SF
SNR?

Green: excess

OB association?

(Baghmanyan et al. 2020, Fermi)

Recently, potential CR excess in some star forming regions is reported.
Also, from the depletion timescale of CO, the ionization rate of 𝜁 ≳ 10−16 s −1
(c.f. the fiducial ISM value 10−17 s −1 ) is favored (e.g. Zhang et al. 2020).
→ Star formation activity itself may be producing cosmic rays?
(Note: other ionization sources like stellar UV and X-ray are also important.)

Why Is This Interesting?

(Küffmeier et al. 2020)• In the first place, we thought that starformation is “low-energy” and did not
expect that it can produce CRs.
• The ionization degree affects the disk
structure via non-ideal MHD effects →• The ionization rate in protoplanetarydisks is set by itself, not by environment.
• The ionization rate in disks can behighly variable both in space and time.
• CRs can trigger complex chemical
reactions in star forming clouds.
Flares (reconnection), jets and shocks
accelerate CRs. (Padovani et al. 2020).
Note: reconnection can be also important
to determine the stellar magnetic flux.

(Takasao et al. 2019, visualization:
T. Takeda @ VASA Entertainment)

How Can We Confirm?

© JAXAXRISM/ATHENA/FORCE etc.
- X-ray flares

ALMA-2 - chemistry triggered by
CR/X-ray (c.f. Cleeves+ 2017)
Takasao et al. 2019

© SKA Organisation

CTA - time-dependent gamma-ray
observations → CRs from bursts

ngVLA (or SKA) - synchrotron,
free-free, small-scale kinematics⇒ Multi-messenger time-domain astronomy in star formation

Star/Disk Scale

Structures in MCs with LST
Complete IMF/CMF with
Roman / PFS / LST
MCs in other Galaxies with
ALMA-2 and ngVLA

Core Scale

Cloud Scale

Cosmological / Galactic Scale

Multi-Scale, Multi-Physics nature of Star Formation

Directly resolving thecore to disks, outflows
and jets with TMT,
ALMA-2 and ngVLA

Outflow
Circumstellar-disk

ProtoStar

Chemical diagnosis
at various scales with
ALMA-2, ngVLA
and GREX-PLUS

Emerging topic:
Multi-messenger
time-domain SF
with CTA, XRISM,
ALMA and ngVLA
Origin of
GW Sources

A Few Words on
HPC in Astrophysics
HPC: High-Performance Computing

Diversifying Needs© NAOJ, ATERUI II

Today, large computing power is necessary in every field →High performance computing is essential research infrastructure.

And computing needs are getting diverse:• Hydrodynamics & radiation - high precision, memory intensive• N-body simulations - computation intensive• Data science - require less precision, IO intensive• Data archive - database / storage technology→ various software and hardware techniques are required.
Therefore, it is of crucial importance for NAOJ to maintain its own
computing center, and flexibly cover various needs, in terms ofboth hardware and software.
(Although, it is also important to collaborate with other centers.)

Just a Few Examples...
Numerical simulations with realistic physics
are now being carried out:
• Cluster formation simulations with feedback
resolving each star: e.g. SIRIUS project →• Non-ideal MHD simulations of star and disk
formation including dust grains ↓• High resolution 3D global disk simulations
directly resolving MRI turbulence(Tsukamoto et al. 2021, star/disk formation
simulation including dust grains)(Hirai et al. 2021, SIRIUS star-by-star
simulations of cluster formation)(Iwasaki et al. in prep., global 3D non-ideal
MHD simulation of a disk resolving MRI)

Toward the Future of HPC
Computing is diversifying but also inflating (c.f. Fugaku: >7x106 cores)

It is not easy to fully utilize large supercomputers.
In the near future, the situation will be actually worse:• “General-purpose” CPUs are not very energy efficient.
• Memory/network per computing resource will shrink.
• GPUs/accelerators require special programming technique.
Also, the code development cost is inflating:• Increasing demand for realistic simulations with more physics• Complicated (often architecture-specific) parallelization/optimization
Buying a larger machine does not mean we can do better research any
more - we need strategic research and development, for both
software and hardware. It is like developing a telescope.
→ NAOJ’s supercomputer is very important to facilitate such initiatives.

NAOJ’s Role (MY Expectation)
It is difficult for university groups to lead such big and long-term projects.
As the center of astronomy in Japan, I want NAOJ to play a leading role.
• Science-driven, mission-oriented, long-term projects• Lead world-wide collaborations• Coordinate large grant programs （e.g. 学術変革 / 特別推進 / 富岳成果創出）• Bridge observations and theories• Database and analysis• Code development• Planning future directions• Outreach and press release• Fostering young generations
Here I am thinking of large projects like
Illustris (MPI) and Enzo (UCSD), andalso DSHARP and eDisk (ALMA LP).
Such initiatives do not necessarily needmuch money - just will and right strategy.

(Illustris, Vogelsberger+)Personal Thoughts on
Future of Our Community
Japanese Version of the Decadal Survey?

Decision Making
The current decision making process in Japan (i.e. Master Plan
led by Science Council of Japan) may not work well any more.
• Categorized by wavelengths and ground vs space- Today’s cutting-edge research is intrinsically multi-messenger- Budgetary limitations - new instruments are expensive→ We have to give up “one telescope per field” at some point• Unclear decision making process- Co-optation (not election) of the SCJ members- The report does not explain why/how each project is selected- Young generations are not actively involved⇒ How can we improve this process?

ASTRO2020 ReleasedMaster Plan vs Decadal Survey
Master Plan

Decadal Survey

Frequency

Every 3 years

Every ~10 years

Organization

SCJ members
Proposals fromeach community(based on wavelengths)

Selected by NAS (sponsored by
NSF, NASA, DOE)
Panels: 6 Science + 5 Program +1 State of the profession>100 (including young) members

TargetOnly big projects

Projects and Policies

Input

34 (physics)

573 +294 whitepapers

Report~ 50 pages, mostly admin.

> 600 pages

OutcomeJust selection results

Detailed recommendation
including budget assessments
e.g. 6m space telescope =(HabEX + LUVOIR) / 2

My Personal Thoughts• We probably cannot afford the cost of the decadal survey→ start from something tractable, including some key essences• What are the key essences?
- Fair and transparent decision making process- Scientific assessments beyond wavelengths (→ science panels)- Detailed assessments including budget and feasibility (“TRACE”)- The selection process and results are respected and trusted.
⇒ Assemble a new committee under the Astronomical Society- The members should be selected by election.
- The members should include young generation.
- Combination of scientific-oriented review and project-oriented review.
- Detailed report should be published.
- The committee members’ effort must be respected and trusted.
- The outcome should be used by the SCJ and other policy makers.

Thank you!