Searching for young, massive, proto-globular clusters in the local Universe

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Institute, Liverpool JMU) Ivan Cabrera-Ziri, Nate Bastian,

1 Searching for young, massive, proto-globular clusters in the local Universe Ben Davies (Astrophysics Research Institute, Liverpool JMU) Ivan Cabrera-Ziri, Nate Bastian, Carmela Lardo, Steve Longmore, Maurizio Salaris, Katie Hollyhead

2 few million Msun Omega Cen - ESO ~12 Gyr globular clusters are still forming in the local universe Antennae - HST few million Msun ~7 Myr

3 Surprise #2: I multiple populations in GCs. Can only be explained by variations in He abundance NGC2808 (Piotto et al. 2007) B-I

4 Surprise #3: Funny abundances anti-correlation between Na-O (Carretta et al. 2006)

5 Surprise #3: Funny abundances anti-correlation between Na-O, C-N M5 (Cohen et al. 2002)

6 Surprise #3: Funny abundances anti-correlation between Na-O, C-N p,γ Implies pollution by CNO-burning stars Na-Ne Cycle 19 F 20 Ne + 1 H 21 Na + γ 21 Na 21 Ne + e + + ν e 21 Ne + 1 H 22 Na + γ 22 Na 22 Ne + e + + ν e 22 Ne + 1 H 23 Na + γ 23 Na + 1 H 20 Ne + 4 He

7 Conclusion: Globular clusters contain discrete, multiple populations of stars: * Primordial (i.e. ~Solar mix of abundances) * Secondary (formed from CNO-polluted gas) Possible CNO-burning polluters: * massive main-sequence stars * Intermediate mass AGB stars

8 Models for the formation of the secondary population

9 Models for the formation of the secondary population

10 Models for the formation of the secondary population * The spinstar (or FRMS) scenario Decressin Credit: William Chantereau

11 Models for the formation of the secondary population * The spinstar (or FRMS) scenario (taken from Krause+ 2006) Step 1

12 Models for the formation of the secondary population * The spinstar (or FRMS) scenario (taken from Krause+ 2006) Step 2 Step 1

13 Models for the formation of the secondary population * The spinstar (or FRMS) scenario (taken from Krause+ 2006) Step 2 Step 1

14 Models for the formation of the secondary population * The spinstar (or FRMS) scenario (taken from Krause+ 2006) Step 3 Step 2

15 Models for the formation of the secondary population * The spinstar (or FRMS) scenario Prediction: Star formation should be happening in star clusters with ages 5-30Myr.

16 Models for the formation of the secondary population * The AGB-scenario (e.g. D Antona & Caloi 2004, Conroy & Spergel 2011)

17 Models for the formation of the secondary population * The AGB-scenario (e.g. D Antona & Caloi 2004, Conroy & Spergel 2011)

18 Models for the formation of the secondary population * The AGB-scenario (e.g. D Antona & Caloi 2004, Conroy & Spergel 2011)

19 Models for the formation of the secondary population * The AGB-scenario (e.g. D Antona & Caloi 2004, Conroy & Spergel 2011) [~100 Myr]

20 Models for the formation of the secondary population * The AGB-scenario Some predictions: (e.g. D Antona & Caloi 2004, Conroy & Spergel 2011) Massive clusters should show age spreads (or multiple bursts). Clusters should retain ejecta and accreted gas for long periods. To have enough material to form the 2nd gen stars, GCs must have been times more massive than presently seen. [~100 Myr]

21 Models for the formation of the secondary population * The AGB-scenario Some predictions: (e.g. D Antona & Caloi 2004, Conroy & Spergel 2011) Massive clusters should show age spreads (or multiple bursts). Clusters should retain ejecta and accreted gas for long periods. To have enough material to form the 2nd gen stars, GCs must have been times more massive than presently seen. [~100 Myr]

22 Models for the formation of the secondary population * The AGB-scenario Some predictions: (e.g. D Antona & Caloi 2004, Conroy & Spergel 2011) Massive clusters should show age spreads (or multiple bursts). Clusters should retain ejecta and accreted gas for long periods. To have enough material to form the 2nd gen stars, GCs must have been times more massive than presently seen. [~100 Myr]

23 Models for the formation of the secondary population Testing the multi-pop GC models All model predict that the secondary population is younger. Impossible to see this in GCs (since Δt << t) However, if YMCs are protoglobular clusters, we should be able to detect evidence of younger populations (or ongoing SF).

24 Models for the formation of the secondary population Testing the multi-pop GC models All model predict that the secondary population is younger. Impossible to see this in GCs (since Δt << t) However, if YMCs are protoglobular clusters, we should be able to detect evidence of younger populations (or ongoing SF). Mission: Study young/intermediate age star clusters, and search for evidence of on-going SF and/or multiple-age populations

25 Evidence of on-going star formation? Bastian et al. 2009

26 Evidence of on-going star formation? Bastian et al. 2009

27 Evidence of on-going star formation? Bastian et al. 2009

28 Evidence of on-going star formation? Bastian, Cabrera-Ziri, Davies, Larsen 2013a All non-detections - spanning a range of ages & masses Can rule out presence of ionised gas > 100Msun Can rule out that emissionline clusters are hiding an older population at mass ratios < 2:1

29 Evidence of on-going star formation? Longmore 2015 Use AGB scenario to predict the amount of extinction due to cold dust: Av (mag) Intermediate age (30-100Myr) clusters should have easily observable reddening/ luminosity profiles. They don t.

30 Evidence of on-going star formation? Myr ALMA observations of the Antennae Cabrera-Ziri et al No gas detected in CO (3-2) (upper limit of <10% cluster mass)

31 Evidence of a second, younger population? NGC 34 Cluster 1

32 Evidence of a second, younger population? NGC 34 Cluster 1 data (Schweizer & Seitzer 2007) single population fit (100Myr) two populations three populations residuals Cabrera-Ziri, Bastian, Davies et al. 2014

33 Evidence of a second, younger population? NGC 34 Cluster 1

34 Evidence of a second, younger population? NGC 34 Cluster 1 measured age of cluster Figure 3. Results of fitting the normalised spectrum of Cluster

35 Evidence of a second, younger population? NGC 34 Cluster 1 measured age of cluster permitted Figure 3. Results of fitting the normalised spectrum of Cluster

36 Evidence of a second, younger population? NGC 34 Cluster 1 measured age of cluster permitted For a mass-ratio ~ 1:1, we can rule out any star-formation ~20Myr after the first burst Figure 3. Results of fitting the normalised spectrum of Cluster

37 But what about intermediate ages in the LMC..? Niederhofer+ 2015

38 But what about intermediate ages in the LMC..? Niederhofer Extended turn-off: age spreads..?

39 But what about intermediate ages in the LMC..? Niederhofer Extended turn-off: age spreads..? Red clump not extended, so probably not

40 Summary so far Young / intermediate age clusters in local Universe match GCs for mass, size. AGB-scenarios for GC formation predict 2nd-generation of starformation ~30-100Myr after the first. Never been seen.

41 More general problems for all GC-formation scenarios Mass budget / mass-loss Most formation models struggle to make a 2nd pop with M2>0.05M1 Need to lose large fraction of pop-1 without losing any pop-2

42 More general problems for all GC-formation scenarios Mass budget / mass-loss 35 GCs (without Fe spreads) Bastian & Lardo 2015

43 More general problems for all GC-formation scenarios Mass budget / mass-loss 98% FG lost 95% FG lost 90% FG lost fenriched(initial) = GCs (without Fe spreads) Bastian & Lardo 2015

44 More general problems for all GC-formation scenarios Mass budget / mass-loss 98% FG lost 95% FG lost Mass loss in a tidal field 90% FG lost Mass loss due to gas expulsion fenriched(initial) = GCs (without Fe spreads) Bastian & Lardo 2015

45 More general problems for all GC-formation scenarios Relative abundance trends abundance yields abundance time

46 More general problems for all GC-formation scenarios Relative abundance trends abundance abundance yields He time

47 More general problems for all GC-formation scenarios Relative abundance trends abundance abundance yields He Na time O

48 More general problems for all GC-formation scenarios Relative abundance trends Bastian, Cabrera-Ziri, Salaris 2015

49 More general problems for all GC-formation scenarios Relative abundance trends Bastian, Cabrera-Ziri, Salaris 2015

50 More general problems for all GC-formation scenarios Relative abundance trends allowed Bastian, Cabrera-Ziri, Salaris 2015

51 More general problems for all GC-formation scenarios Relative abundance trends Too much Na-O processing for amount of He? allowed Bastian, Cabrera-Ziri, Salaris 2015

52 More general problems for all GC-formation scenarios Relative abundance trends Too much Na-O processing for amount of He? AGBs AGBs FRMS Binaries Bastian, Cabrera-Ziri, Salaris 2015

53 Summary overall Searching for young, massive, proto-globular clusters in the local Universe Main-sequence striations and Na-O / C-N anticorrelations indicate GCs experience a second star-formation event, fuelled by CNO-processed gas. Young / intermediate age massive clusters should do the same, and we should be able to see evidence of it. We haven t (yet). Strongly argues against any model put forward to date*. New ideas needed! *Unless you start e.g. fiddling with the IMF

The Origin of Multiple Populations within Stellar Clusters An Unsolved Problem

The Origin of Multiple Populations within Stellar Clusters An Unsolved Problem Nate Bastian (Liverpool, LJMU) Ivan Cabrera-Ziri (LJMU), Katie Hollyhead (LJMU), Florian Niederhofer (LMU/ESO) V (brightness)