bimodal regime in young massive clusters leading to ... · introduction motivation: cooling winds...

Bimodal regime in young massive clusters leadingto formation of subsequent stellar generations

Richard WünschJ. Palouš, G. Tenorio-Tagle, C. Muñoz-Tuñón, S. Ehlerová

Astronomical institute, Czech Academy of Sciences

14th August 2015

Wünsch (AsU CAS) 2G with bimodal regime 14.8.2015 1 / 1

Introduction

Motivation: Cooling winds→ multiple populations

young massive clusters have windsstellar winds, SNe→ collisions→ hot shocked wind→ outflow

the wind may become thermally unstable inside the clusterif the cluster is massive and compact enough

dense warm/cold clumps are formeddepends whether they can self-shield against ionising stellar radiation

new stars form either in-situ or after clumps sink into the centre2nd generation (2G) stars enriched by products of massive stars chemical evolution

similarities with FRMS scenario (desressin+07)

- even fast winds can be captured

predicts formation of 2G stars in the centre (may help with mass budget problem)

Introduction

The cluster wind

Star cluster wind: semi-analytical model

by Chevalier & Clegg (1985, Nat., 317, 44)Ekin of stellar winds and SN ejectathermalized, hot gas fills the clustersources (stars) distributed according totop-hat profilesolution of 1D spherically sym. HDequations, cooling neglectedsonic point at the cluster bordertested by Cantó+00, Raga+01 and othersfor stellar windsinteraction of the wind with the parentalcloud not covered here(harper-clark&murray09, krause+12,14, rogers&pittard13,

rosen+14, herrera+, . . . )

The cluster wind

Catastrophic cooling of the windfor massive clusters, cooling has to betaken into accountradiative solution by silich+03→ T drops at a certain radiuspredicts different observed X-ray flux(silich+04) - good agreement withobserved X-ray fluxes(NGC4303 nuclear SSC; jiménez-bailón+03)

above certain mass limit, no stationary wind solution exists→catastrophic cooling (silich+03):

energy deposition ∝ MSC

cooling ∝ ρ2wind ∝ M2

}⇒ inevitable

tenorio-tagle+05 suggests extreme positive feedback (high SFE)

The cluster wind

Catastrophic cooling of the windfor massive clusters, cooling has to betaken into accountradiative solution by silich+03→ T drops at a certain radiuspredicts different observed X-ray flux(silich+04) - good agreement withobserved X-ray fluxes(NGC4303 nuclear SSC; jiménez-bailón+03)

above certain mass limit, no stationary wind solution exists→catastrophic cooling (silich+03):

energy deposition ∝ MSC

cooling ∝ ρ2wind ∝ M2

}⇒ inevitable

tenorio-tagle+05 suggests extreme positive feedback (high SFE)

Bimodal regime

Three wind regimes

quasi-adiabatic regimeidentical with CC85, cooling has no effectmechanical luminosity (cluster mass) substantially below Lcrit

3 parameters: LSC , MSC︸︷︷︸given by MSC

density

Quasi− v < c

vA,∞ =√

2ηLSC

thermalization

−adiabatic

sound speed

temperature

velocity

Bimodal regime

Three wind regimes

radiative regimemechanical luminosity (cluster mass) slightly below Lcritwind cools down at certain distance out of the cluster

Radiative density

velocity

temperature

Bimodal regime

Three wind regimes

bimodal regime (tenorio-tagle+07; wünsch+08), cluster split by Rstouter: wind, stationary solution existsinner: thermal instabilities, mass accumulation - secondary SF

Bimodalvelocity

temperature

density

stagnationradius

Bimodal regime

Heating efficiency and mass loading

hot gas inside cluster seems to be colder than energy / massdeposited by stars→ two new parameters:

ηML: mass loading - additional (pristine) gas added to the hot phaseηHE: heating efficiency - some thermal energy is lost from the hotphase (on the top of standard cooling)

mass loading - evidence for mixing with pristine gas ∼ 1 : 1(e.g. prantzos+07)

obs. evidence for low heating efficiencymissing energy from X-ray luminosities(rosen+14)recombination line profiles of SSCs inAntennae have moderately supersonicwidths (gilbert&graham07)

Bimodal regime

Heating efficiency 2

HII region coinciding with SSCs in M82 are very compact(silich+09)

evidence for high heating efficiency in M82defined globally: ηHE = 30− 100 %, strickland&heckman09)

Bimodal regime

Heating efficiency 2

HII region coinciding with SSCs in M82 are very compact(silich+09)

evidence for high heating efficiency in M82defined globally: ηHE = 30− 100 %, strickland&heckman09)

Bimodal regime

Evolution of Massive Compact Clusters (wünsch+11)

evolution of the critical luminosity (Lcrit) for 107 M� cluster withRSC = 3 pcStarburst99 with Geneva evolutionary tracks (HighMass winds)

0 5 10 15 20 25 30 35 40

crit [e

t [Myr]

Lcrit: ηhe=1, ηml=0

Lcrit: ηhe=0.05, ηml=1

Bimodal regime

Influence of ionising radiation

Analytical estimate (palouš+14)dense warm gas sinks into centre: stream + centralclumpself-shielding mass of the central clumpmself = NUV,SC

µmHα?

kTionPhot

can streams of falling mass cool before they fall intocentre?tSS = 1

4πq2UV R5

SCR−2st (1 + ηml)

−1M−1SCµmHα

−2∗

(kTPhot

central clump

ionisedP

HealPix ray/cone

target cell

tree node

RHD simulations:radiation treated by TreeRay: tree + reverseray-tracing; wünsch+(in prep.)

Bimodal regime

µmHα?

kTionPhot

4πq2UV R5

−1M−1SCµmHα

−2∗

(kTPhot

central clump

ionisedP

HealPix ray/cone

target cell

tree node

Bimodal regime

µmHα?

kTionPhot

4πq2UV R5

−1M−1SCµmHα

−2∗

(kTPhot

central clump

ionisedP

HealPix ray/cone

target cell

tree node

Bimodal regime Simulations

RHD simulation

AMR code Flash

1283 grid

M&E src: Schusterdistribution

optically thincooling:raymond+76

fixed stellar gravity

self-gravity: treecode (wünsch+15)

heating by ionisingradiation: TreeRay

Evolution of accumulated mass

0 0.5 1 1.5 2 2.5 3 3.5 4 2

ass [M

time [Myr]

Msc = 107 MSun, β = 1.5, Rh = 2.38 pc, ηHE = 0.05, ηML = 1.0

firstsupernova

total mass insertedsinks+gas

sinksgas

windcal

Evolution of accumulated mass

0 0.5 1 1.5 2 2.5 3 3.5 4 2

ass [M

time [Myr]

Msc = 107 MSun, β = 1.5, Rh = 2.38 pc, ηHE = 0.05, ηML = 1.0

firstsupernova

total mass insertedsinks+gas

sinksgas

windcal

Mass budget at 3.5 Myr:1G stellar mass: 107 M�inserted by winds: 4× 105 M�mass loaded: 4× 105 M�2G stellar mass: 7× 105 M�→ very compact, in the centre→ should stay in the cluster during1G tidal removal (khalaj&baumgardt15)

remains in dense phase: 14000 M�→ rapidly removed by SNe

Parameter space study

0.001 0.01 0.1 1

bimodal butno self-shielding

not bimodal

extended 2G

Summary & conclusions

Summary

wind cooling leading to bimodal regime is inevitable for high andcompact enough clusterdense gas formed by thermal instability stays in the cluster andself-shields against ionising radiation→ secondary SFheating efficiency⇒ compact/extended 2G

low heating efficiency→ SF in the central clump: 2G concentratedin the cluster centre;high heating efficiency→ SF in streams: 2G dispersed throughoutthe cluster

much more difficult to capture SN ejecta; rapidly removeremaining accumulated gas

Summary

Thank you!

bimodal regime in young massive clusters leading to ... · introduction motivation: cooling winds...

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