Blurring thestar cluster - galaxy divide
Anna Lisa Varri
UKRI Future Leaders Fellow | Univ. of Edinburgh ⇄ Univ. of Tokyoin collaboration withPhil Breen, Jorge Peñarrubia (Edinburgh),
Douglas Heggie (Edinburgh), Kate Daniel (Bryn Mawr)
Annette Ferguson, Pete Kuzma, Ruben Sanchez-Janssen (Edinburgh)Michiko Fujii, Naoki Yoshida (UTokyo),
Yuya Sakurai (Georgia Tech), Yutaka Hirai (RIKEN Kobe)

A new observational landscape
Local Universe (Gaia, HST)

Early Universe (waiting for JWST, ELTs ...)

Synergy between Gaia and HST proper motions,plus high-quality spectroscopy (e.g., Gaia-ESO,WEAVE, MOONS, 4MOST ...) will unlock for the first time
the full phase space of several nearby globular clusters.

Star-forming sources in Hubble Frontier Field
as precursor of globular clusters?
Bouwens+ 2017a,b ApJ, Elmegreen^2 2017 ApJL,
Vanzella+ 2017a,b ApJ, 2019a,b MNRAS,Renzini+ 2017, Pozzetti+2019

See talks on Day 3

A new computational landscape
Gravitational million-body problem ‘solved’Towards GC formation in a cosmological context

DRAGON N-body simulations | Wang+ 2016 ApJN-body model of M4 | Heggie 2014 MNRAS

Evolution of GCs in CosmoGrid | Rieder+2013, Ishiyama+ 2013 MNRAS,Renaud+ 2017 MNRAS; Carlberg 2017 ApJ; Li, Gnedin^2 2017 ApJ …
… also, role during reionization? Ricotti 2004, Boylan-Kolchin 2017a,b ...

See Naoto Yoshinari’s talkWhen (a dynamicist’s) life was simple
Ellipticals and bulges
R_eff ~ 5 kpc; M ~ -22Star clusters(Galactic and extragalactic)
R_eff ~5 pc; M ~ -7

When (a dynamicist’s) life is a nightmare
Ultra-faint ‘satellites’ [lots of DM?]r_eff > 20 pc; M < -3.5
Hydra II, Laevens 2, Pegasus III, Ret II, Eridanus II, Tucana II,
Horologium I, Pictoris I, Phoenix II, Draco II, Sagittarius II,
Horologium II, Grus II, Tucana III, Columba I, Tucana IV,
Reticulum III, Tucana V, Crater 2, Acquarius 2, Pictoris II,
Segue 1

Extended clusters, ‘faint fuzzies’ [no DM?]
10 pc < r_eff < 20 pc
Discovered in outskirts of MW, M31, M33, many Local dwarfs ...

Ultra-faint star clusters [no DM?]r_eff < 20 pc; M < -3.5
Segue 3, Munoz 1, Balbinot 1, Laevens 1/Crater,Laevens 3, Kim 1, Kim 2, Eridanus III, DES 1, Kim 3

Ultra-compact dwarfs [DM? central BH?]
massive globulars or stripped dwarfs?

Misgeld & Hilker 2011 MNRAS, see also AIMSS project (Norris et al. 2014)

Some recent oddities in globulars
Growing number of (very) extended,spherical, tenuous halo of stars
surrounding globulars

Growing number of clusters
with untruncated, flattened
velocity dispersion profiles

Kuzma et al. 2017,2018 MNRAS, first noted by Olszewski et al. 2009(see also M2, NGC 5694, M92 … by Correnti et al. 2011,Piatti et al. 2017, 2018, Sollima et al. 2018). More with Gaia!
Marino et al. 2014 MNRAS (see also M15, ω Cen, M92, NGC 5694 …
by Drukier et al. 1997,1998, Da Costa 2012, Bellazzini et al. 2015)

Existence of high velocity stars(“Cannonballs” in 47 Tuc, Meylan et al. 1990 A&A)

On the bright side‘ potential escapers’
energetically unbound stars which are confinedwithin the critical Jacobi equipotential surface

Kuepper, Kroupa, Baumgardt, Heggie 2010 MNRAS
see also Claydon, Gieles, Zocchi 2017 MNRAS

On the bright side
First (approximate) analytic model of a star clusterthat includes potential escapers

Inspired by Hénon’s family “ f ” (periodic orbits, among solutions of the circular Hill’s problem)
High-inclination orbits behave as Lidov-Kozai theory (in quadrupole approximation)

On the bright side
First (approximate) analytic model of a star clusterthat includes potential escapers
Kepler energy, averaged over Kepler motions

z-component of angular momentum, averaged over Kepler
and orbital motions

Three integral of motion used to identify ‘potential escapers’in phase space (via discrimination criterion)

Daniel, Heggie, Varri 2017 MNRAS
see also Claydon, Gieles, Varri et al. 2019 MNRASADS title search for “dark matter” AND “globular clusters”
5Dark matter in globular clusters

3.75
Dark matter and theorigin of galaxies andglobular star clusters

2.5

1.25

01984 1989 1992 1995 1998 2001 2004 2007 2010 2013 201650 entries

On the dark side
Stellar envelopes of globular clusters
embedded in dark matter mini-halos

Peñarrubia,Varri, Breen et al. 2017 MNRAS Lett

On the dark side
Stellar envelopes of globular clusters
embedded in dark matter mini-halos
Peñarrubia,Varri, Breen et al. 2017 MNRAS Lett.

Ellipticals as end-products of violent relaxation, see also Bertin & Stiavelli 1984, Jaffe 1987, Makino 1990, Aguilar 2008Collisional dynamics with dark matter
A possible dynamical framework to interpret the uncharted territory between ‘star clusters’ and ‘galaxies’

N-body simulations with‘live’ dark matter halocurrently in progress(with Michiko Fujii’s Bridge)
Non-trivial role of tides
still to be addressed

Breen, Varri, Peñarrubia et al. to be submitted

Caveat!

Parting thoughts
The presence of a dark halo changes dramaticallythe dynamical evolution of collisional stellar systems.
Refreshingly new take on the classical paradigm.
The moment of core collapse gets delayed, the size of the core changes,
the core-halo gravothermodynamics is different … so much to explore!

We might gain a new framework to explore the uncharted territory
between collisional and collisionless dynamical systems.
Some zoo-keeping at the low-end of the galaxy mass function is very much needed.

The star cluster - galaxy divide is the small-scale frontier ofgalaxy formation and a central challenge for ‘near-field’
cosmology in the era of Gaia, JWST, ELTs.
Deep implications for fundamental physics - dark matter clustering scale and beyond.

I am based at UTokyo (in Fujii’s Group) until Nov. 2019 - let’s talk about low-mass stellar systems!
Hongo, Science Bldg.1, 11F

annalisa.varri@gmail.com@parallasseh