Multiple populations in GCs: constraints on formation scenarios from kinematics & dynamics Vincent Hénault-Brunet Mark Gieles Oscar Agertz Justin Read Alice Zocchi IAU 316: Formation, evolution, and survival of massive star clusters
Chemistry (hydro) Dynamics [Na/Fe] What is the source of pollution? ~70% anomalous () ~% normal () [O/Fe] How to get this polluting material into a large fraction of GC stars? - Multiple generations of star formation? e.g. D Ercole+ 08 - Accretion onto low-mass PMS stars? Bastian+ 13 - Something completely different?? ICs long-term dynamical evolution
GCs are collisional systems Mixing Mass segregation energy mean radius low-mass stars high-mass stars BHs angular momentum e.g. Hénault-Brunet+ 15; Vesperini+ 13 Decressin+ 08 time Aarseth 12
Spatial distribution & kinematics of subpopulations Nature vs Nurture 2 3/2 hv i trl / hmi - longer relaxation time - less mixing - imprints of formation? - shorter relaxation time - more mixing - mass segregation?
Spatial and kinematic mixing of subpopulations Complete spatial mixing when 60-70% of mass lost due to two-body relaxation Rh() / Rh() 60% mass lost Lagrangian radii [pc] 10 2 10 1 10 0 10 1 10 2 MGEN1-nosev 60% mass lost 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 M / M0 M(t)/M 0 M / M0 Vesperini+ 13 Hénault-Brunet+ 15
Spatial and kinematic mixing of subpopulations Complete spatial mixing when 60-70% of mass lost due to two-body relaxation Same applies to kinematic differences between populations Peak rotation max hvfi [nbody] 0.8 0.7 0.6 0.5 0.4 0.3 0.2 global pristine polluted 60% mass all lost MGEN1-nosev 0.1 0.0 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 M(t)/M 0 M / M0 Hénault-Brunet+ 15; see also Decressin+ 08
Spatial and kinematic mixing of subpopulations Some memory of ICs should be preserved in outer parts of many GCs 10 7 10 6 47 Tuc expansion dominated M M [M ] ] 10 5 10 4 NGC 6362 10 3 evaporation dominated 10 2 10 1 10 0 10 1 10 2 10 3 R G RG [kpc] see Gieles, Heggie, Zhao 11 data from Harris catalogue
Observations: spatial distribution and kinematics Enriched population -> more centrally concentrated e.g. Lardo+ 11 Enriched population -> lower velocity dispersion (when kinematic differences are found) e.g. Bellazzini+ 12, Kucinskas+ 14
Observations: spatial distribution and kinematics 47 Tuc - HST proper motions near R ~2 rh Enriched stars -> more radially anisotropic velocity distribution Richer+ 13 PM dispersion [mas/yr] color group
Observations: spatial distribution and kinematics NGC 2808 - HST proper motions Bellini+ 15 Enriched stars -> more radially anisotropic velocity distribution beyond R ~ rh rh 1.5 rh 2 rh rh 1.5 rh 2 rh tan/ rad 1
On the uniqueness of the observed signatures N-body simulations scaled to 47 Tuc Disc embedded in spherical cluster Spherical subsystem within spherical cluster Hénault-Brunet+ 15; see also Mastrobuono-Battisti & Perets 13
Clues from differential rotation of subpopulations? Formation of 2nd generation -> flattened and rotating pop. (Bekki 10, 11) Removing >90% of 1st generation removes large fraction of its angular momentum Enriched stars on preferentially radial orbits -> less rotation Marginal evidence in clusters from Bellazzini+ 12 Rotation curve hvfi [km/s] 2.0 10 0 10 1 10 0 10 1 r [pc] 10 1 10 0 10 1 r [pc] t = 0 t = 0 Hénault-Brunet+ 15
Clues from differential rotation of subpopulations? hvfi [km/s] Formation of 2nd generation -> flattened and rotating pop. 10 MGEN1 t=0 Myr (Bekki 10, 11) Removing >90% of 1st generation removes large fraction of its angular momentum pristine polluted Enriched stars on preferentially radial orbits -> less rotation Marginal evidence in clusters from Bellazzini+ 12 ACC1 t=0 Myr pristine polluted Rotation curve hvfi [km/s] hvfi [km/s] [km/s] 0 2.0 10 10 0 MGEN1 t=346 Myr 10 1 10 0 10 1 MGEN1 t=1386 Myr r [pc] ACC1 t=346 Myr 10 1 10 0 10 1 r [pc] t = 0.3 t = Gyr 0 t = 0.3 t = Gyr 0 ACC1 t=1386 Myr Hénault-Brunet+ 15
Clues from differential rotation of subpopulations? hvfi [km/s] hvfi [km/s] 10 MGEN1 t=0 Myr Formation of 2nd generation -> flattened and rotating pop. 10 MGEN1 t=346 Myr pristine polluted (Bekki 10, 11) Removing 0 >90% of 1st generation removes large fraction of its angular momentum ACC1 t=0 Myr pristine polluted Enriched stars on preferentially radial orbits -> less rotation Marginal evidence in clusters from Bellazzini+ 12 ACC1 t=346 Myr Rotation curve hvfi [km/s] hvfi [km/s] [km/s] 0 2.0 10 10 0 0 MGEN1 t=1386 Myr 10 1 10 0 10 1 MGEN1 t=10745 Myr r [pc] ACC1 t=1386 Myr 10 1 10 0 10 1 r [pc] t = 1 t Gyr = 0 t = 1 t Gyr = 0 ACC1 t=10745 Myr Hénault-Brunet+ 15
hvfi [k 10 Clues from differential rotation of subpopulations? 0 hvfi [km/s] hvfi [km/s] Formation MGEN1 of 2nd generation t=346 Myr -> flattened and rotating pop. 10 10 MGEN1 t=1386 Myr (Bekki 10, 11) Removing >90% of 1st generation 0 removes large fraction of its angular momentum Enriched stars on preferentially radial orbits -> less rotation ACC1 t=346 Myr Marginal evidence in clusters from Bellazzini+ 12 ACC1 t=1386 Myr Rotation curve hvfi [km/s] hvfi [km/s] 0 2.0 10 0 MGEN1 t=10745 Myr 10 1 10 0 10 1 r [pc] r [pc] ACC1 t=10745 Myr 10 1 10 0 10 1 r [pc] r [pc] t = 11 t Gyr = 0 t = 11 t Gyr = 0 10 1 10 0 10 1 Hénault-Brunet+ 15
Spatial distribution of subpopulations: central regions of M15 Primordial population more centrally concentrated than population! Larsen+ 15
Spatial distribution of subpopulations: central regions of M15 Mass segregation? -> need Δm ~ 0.25 M -> If due to helium spread -> ΔY = 0.15 (inconsistent with CMD) Normalized surface density M15 log(r) [pc] Larsen+ 15
Spatial distribution in central regions: additional considerations - What about binaries? larger binary fraction for stars (12% vs 1%; D Orazi+ 10) larger core binary fraction? core binary fraction global binary fraction Hurley+ 07 Larsen+ 15
Spatial distribution in central regions: additional considerations - What about binaries? larger binary fraction for stars (12% vs 1%; D Orazi+ 10) larger core binary fraction? - Other clusters? NGC 2808: no significant difference in spatial distribution of evolved stars D Alessandro+ 11; Iannicola+ 09 NGC 2419: giants with blue u-v colors more centrally concentrated Beccari+ 13; see also Larsen+ 15 * effect of mass segregation sensitive to cluster concentration
Multi-mass model using limepy (Gieles & Zocchi 15) M 15 NGC 2808 surface brightness l.o.s. velocity dispersion
Multi-mass model using limepy (Gieles & Zocchi 15) Effect of mass segregation maximal in densest clusters like M15. M 15 NGC 2808
Multi-mass model using limepy (Gieles & Zocchi 15) Effect of mass segregation maximal in densest clusters like M15. M 15 NGC 2808 + 0.25 M + 0.25 M
Spatial distribution in central regions: additional considerations - What about binaries? larger binary fraction for stars (12% vs 1%; D Orazi+ 10) larger core binary fraction? - Other clusters? NGC 2808: no significant difference in spatial distribution of evolved stars D Alessandro+ 11; Iannicola+ 09 NGC 2419: giants with blue u-v colors more centrally concentrated Beccari+ 13; see also Larsen+ 15 * effect of mass segregation sensitive to cluster concentration - Initial conditions matter
Conclusions - Spatial/kinematic imprints of the formation of multiple populations can survive to the present day - All observations consistent with an population forming more centrally concentrated - None of the observed signatures unique to a given formation scenario. Differential rotation may provide useful constraints. - Explaining the more centrally concentrated population in the inner regions of M15 in terms of mass segregation remains challenging - Could binaries play a role??