The epoch o acc e ion o Milky Way
dwa s om Gaia DR3
IAU H1 – The Local uni e se Semina - 25 No embe 2025
P esen ed by F ançois Hamme
LIRA
F om Gaia DR2 o DR3
Li, Hamme , Babusiaux e al. (2021):
Ba aglia, Taibi, Thomas e al. (2022):
46 dwa galaxies
ull accoun o Gaia sys ema ics
66 dwa galaxies wi h eliable measu emen s
Bayesian me hod
Two pape s on dwa o bi s based on Gaia DR3:
•The numbe o s a s ha ha e combined adial eloci ies & p ope mo ions (3D):
inc eases om 7 224 631 o 33 812 183
•P ope mo ion unce ain y is di ided by ~ 2
•Pa allax unce ain y is di ided by ~ 1.3
è Binding ene gy and angula momen um o dwa o bi s wi h e y good accu acy
Con en
1- In all ime e sus binding ene gy: he MW acc e ion his o y
2- Gaia p edic s a ecen in all (< 3 Gy ago) o mos MW dSph galaxies: i
is con i med by he p esence o young s a s
3- Consequences on dSph o ma ion and on hei da k ma e con en
4- Conclusions
F ançois Hamme
1- In all ime e sus binding ene gy:
he acc e ion his o y o he MW
F ançois Hamme
The halo acc e ion his o y
Rocha e al. 2012
P edic ion o he hie a chical scena io :
•Galaxy mass g ows wi h ime, sa elli es
a i ed he i s a e he mos bound, while
he newcome s a e he leas bound (Go ,
1975, “onion model”)
•P o en by all cosmological simula ions,
e.g., Rocha e al. 2012, Boylan-Kolchin e
al. 2013
Consis en wi h he p edic ion o he
hie a chical scena io :
•Galaxy mass g ows wi h ime, sa elli es
a i ed he i s a e he mos bound, while
he newcome s a e he leas bound (Go ,
1975, “onion model”)
•P o en by cosmological simula ions, e.g.,
Rocha e al. 2012, Boylan-Kolchin e al.
2013, also because he Milky Way has a
ela i ely quie me ge his o y (when
compa ed o e.g., M31, Cen A).
Ebinding = - Eo bi al= -(K + F)
4000 2000 0 -2000 -4000
Lz(km s-1 kpc)
0.5
1.5
1.0
2.0
2.5
Binding Ene gy (105km2s-2)
GSE
Disk
Sg
Bulge
The Milky way halo acc e ion his o y
Adap ed om Callingham e al. (2022) and Deason & Beloku o (2025)
12.5 Gy
9 Gy
6 Gy
4000 2000 0 -2000 -4000
Lz(km s-1 kpc)
0.5
1.5
1.0
2.0
2.5
Binding Ene gy (105km2s-2)
GSE
Disk
Sg
Bulge
The Milky way halo acc e ion his o y
Poin s om s a s
E o ba s om associa ed GCs
12.5 Gy
9 Gy
6 Gy
Ruiz-La a e al. 2022
4000 2000 0 -2000 -4000
Lz(km s-1 kpc)
0.5
1.5
1.0
2.0
2.5
Binding Ene gy (105km2s-2)
GSE
Disk
Sg
Bulge
Mos dSph galaxies a e newcome s in o he MW halo
Poin s om s a s
E o ba s om associa ed GCs
12.5 Gy
9 Gy
6 Gy
< 3 Gy
Binding ene gy based om accu a e
3D eloci ies p o ided by Gaia DR3
Hamme e al. 2021, 2023
Can we use he ela ion be ween in all ime and
binding ene gy o p edic dwa in all epoch?
D’Souza & Bell (2022) s udied he ELVIS simula ion sui e ( om 1 o 3 1012 Msun ). They con i m he
s ong ela ionship be ween Ebinding and Tacc o 45 o he 48 s udied main halo his o ies.
iDouglas
Recen s a o ma ion in all MW dSphs
Y. Yang , E.Caffau, P. Boni acio, F. Hamme , H. Wang, G. Mamon 2024, A&A 691, 363
A e PM- il e
Be o e P ope -Mo ion - il e ing
All Gaia sou ces in < 1.1 deg ee o Sculp o
A e P ope -Mo ion - il e ing Model: 86% o > 10 Gy s a s + 14% a < 2 Gy
Fo nax
2.1 deg ees
✔
UMi D aco Sex ans Ca inaSculp o
✔✔✔✔
✔
Gaia s a
Coun s
Images
S a o ma ion < 2 Gy ago in all dSphs!
3- DSph la e a i als: consequences on hei
( ans) o ma ion and on hei da k ma e con en
F ançois Hamme
•Simula ion pe o med wi h GIZMO (Hopkins 2014), am
p essu e is due o he same Galac ic co onae ha i well
he Magellanic s eam o ma ion (see Wang e al. 2019);
Ram p essu e helps o cap u e he Sculp o p ogeni o .
•Gas ully los nea pe icen e passage: his shaking p ocess
leads o la ge eloci y dispe sions (Wang e al. 2024).
As newcome s in o he halo, dSph gas- ich p ogeni o s
a e loosing hei gas and become ou o equilib ium
Dwa mo ion
Wang e al. 2024
He e, la ge slos alues a e
caused by u bulence,
shocks, ides and gas
losses: he Sculp o
p ogeni o is ans o med
in less han a single o bi !
da k ma e ee Sculp o
Dwa gas (cyan do s) is comp essed by he Galac ic co ona inducing s a
o ma ion and supe no as, which explosions expell he gas o dwa ou ski s
Galac ic co ona densi y inc eases du ing he all o he dwa , and i becomes e y
e ec i e o emo e p og essi ely he dwa gas and o ee he s a s (o ange do s)
Dwa mo ion
o he Galaxy
•I o a ionally suppo ed dSph p ogeni o s we e da k ma e domina ed, his would
p e en hem o be ans o med in o dispe sion suppo ed sys ems;
•This is because da k ma e shields s ella con en and p ese e hei ini ial dynamics.
As newcome s in o he halo, i da k ma e domina ed,
dSph gas- ich p ogeni o s a e also loosing hei gas
Wang e al. 2024
He e, la ge slos alues a e
caused by u bulence,
shocks, ides and gas
losses: he Sculp o
p ogeni o is ans o med
in less han a single o bi !
Sculp o domina ed by da k ma e
Conclusions
F ançois Hamme
•Dwa a e age binding ene gy is 5 (3) imes smalle han ha o GSE (Sg ), espec i ely, sugges ing hei
in all ≤ 3 Gy ago, du ing which hey pe o m less han a single o bi ;
•Thei p ogeni o s a e gas- ich, o a ion-suppo ed: o ans o m hem in sho imes in o dispe sion
domina ed dSph equi es hem o be ou o equilib ium, and his could explain hei high slos alues;
•This howe e equi es a small da k ma e con en in he p ogeni o s (e.g., WLM ype, Kolhe e al. 2026,
A&A submi ed) because massi e DM halo would p e en such a as ans o ma ion.
Conclusions
F ançois Hamme
•Dwa a e age binding ene gy is 5 (3) imes smalle han ha o GSE (Sg ), espec i ely, sugges ing hei
in all ≤ 3 Gy ago, du ing which hey pe o m less han a single o bi ;
•Thei p ogeni o s a e gas- ich, o a ion-suppo ed: o ans o m hem in sho imes in o dispe sion
domina ed dSph equi es hem o be ou o equilib ium, and his could explain hei high slos alues;
•This howe e equi es a small da k ma e con en in he p ogeni o s (e.g., WLM ype, Kolhe e al. 2026,
A&A submi ed) because massi e DM halo would p e en such a as ans o ma ion.
•Recen a i al o dSphs con i med by he disco e y o young (CHEB) s a s by Yang e al. 2024;
•Expansion o he s ella con en a e gas exhaus ion well explain he p esence o s a s e y a om he
dwa cen e s (Ses i o+2023, Walle +2023, Tau+2024, see also wo ks o Ani ud h Chi i, Jaclyn Jensen)
Conclusions
F ançois Hamme
•Dwa a e age binding ene gy is 5 (3) imes smalle han ha o GSE (Sg ), espec i ely, sugges ing hei
in all ≤ 3 Gy ago, i.e., hey can’ p oceed e en a single o bi ;
•Thei p ogeni o s a e gas- ich, o a ion-suppo ed: o ans o m hem in sho imes in o dispe sion
domina ed dSph equi es hem o be ou o equilib ium, and his could explain hei high slos alues;
•This howe e equi es a small da k ma e con en in he p ogeni o s (e.g., WLM ype, Kolhe e al. 2026,
A&A submi ed) because massi e DM halo would p e en such a as ans o ma ion.
•Recen a i al o dSphs con i med by he disco e y o young (CHEB) s a s by Yang e al. 2024;
•Expansion o he s ella con en a e gas exhaus ion well explain he p esence o s a s e y a om he
dwa cen e s (Ses i o+2023, Walle +2023, Tau+2024, see also wo ks o Ani ud h Chi i, Jaclyn Jensen)
•Consequen ly, dwa o bi s canno be used o es ima e he Milky Way mass;
•Keep pos ed o a ull hyd odynamical model o he Milky Way o med om GSE me ge (Akib e al. in
p epa a ion). I also demons a es ha globula clus e s keep hei ene gy om hei p ogeni o s!
F ançois Hamme
Akib e al. in p epa a ion
An explana ion o he in e nal kinema ics o dwa galaxies
wi hou p ominen da k ma e sub-halos
Hamme , Li, Mamon, Pawlowski, Boni acio, Jiao, Wang, Wang & Yang, 2023, MNRAS 519, 5059
The ecen in all o dwa sphe oidal galaxies and hei p ogeni o s o be gas- ich dwa i egula
Hamme , Wang, Mamon, Pawlowski, Yang, Jiao, Li, Boni acio, Ca au & Wang, 2024, MNRAS 527, 2718
Mechanisms o o m dwa s sphe oidal om dwa i egula : he ole o am-p essu e and idal shocks
Wang, Hamme , Mamon, Pawloswki, Yang & Wang, 2024, MNRAS 527, 7144
Hyd odynamical simula ions o ans o m dwa i egula in o dwa sphe oidal
Yang, Ca au, Boni acio, Hamme , Wang, Mamon, 2024, A&A 691, 363
An addi ional p oo o a ecen in all: de ec ion o young s a s in all dwa sphe oidal galaxies
Hamme , Jiao, Mamon, e al. 2024, A&A, 692, 1
The Milky Way acc e ion his o y compa ed o cosmological simula ions: om bulge o ma ion o dwa galaxy in all
