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Observational Constraints on Clustered Star Formation - a More Complete Picture of Clustered Star Formation Emerging

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Observational Constraints on Clustered Star Formation - a More Complete Picture of Clustered Star Formation Emerging Observational constraints on clustered star formation - A more complete picture of clustered star formation emerging Susanne Pfalzner Max-Planck-Institut für Radioastronomie, Bonn, Germany S. Pfalzner August 2018 STARTING POINT • Most stars form in clusters • Clusters span wide range of masses and sizes • Most clusters dissolve within 10 Myr • Clusters that survive are initially more massive Which additional information do observations give us to guide theories of clustered star formation? S. Pfalzner August 2018 MASS-RADIUS RELATION FOR EMBEDDED CLUSTERS Cyg OB2 20000 NGC 6611 Clusters span wide IC 1805 10000 NGC 2244 range of masses and 5000 NGC 7380 Ori 1b sizes, BUT ... ] 2000 sun 1000 ONC 500 ONC 1 200 IC 348 2 100 50 cluster mass [M Cha I 2 T4 Lupus 3 20 T2 T6 T7 Cha I 3 T3 T5 10 T1 T8 Cha I 1 5 IC348 1 0.1 0.2 0.3 0.5 0.7 1 1.5 2 3 4 65 cluster radius (pc) August 2018 Pfalzner, 2009, Pfalzner et al. 2016 S. Pfalzner MASS-RADIUS RELATION FOR EMBEDDED CLUSTERS Cyg OB2 20000 NGC 6611 Clusters span wide IC 1805 10000 NGC 2244 range of masses and 5000 NGC 7380 Ori 1b sizes, BUT ... ] 2000 NGC 6231 sun 1000 Stock 8 ONC Not anything goes 500 ONC 1 200 IC 348 2 Mass-radius relation 100 50 cluster mass [M Cha I 2 holds over many orders T4 Lupus 3 20 T2 T6 T7 of magnitude Cha I 3 T8 T3 T5 10 T1 Kuhn et al 2017 Cha I 1 Jose et al. 2017 5 IC348 1 0.1 0.2 0.3 0.5 0.7 1 1.5 2 3 4 65 cluster radius (pc) Pfalzner et al. 2016 S. Pfalzner August 2018 MASS-RADIUS RELATION FOR CORES Slope for mass radius 20000 relation for clusters and 10000 5000 cores approximately the ] same sun 2000 1000 clumps clusters 500 200 100 cluster mass [M 50 20 10 5 0.1 0.2 0.3 0.5 0.7 1 1.5 2 3 4 65 cluster radius (pc) UrQuhart et al. 2014 S. Pfalzner August 2018 CONSTRAINTS FOR THEORIES Core relation: Forbidden area constraints for initial 20000 for initial conditions conditions 10000 5000 ] sun 2000 Cluster relation 1000 clumps clusters Constraints for conditions 500 at end of formation 200 100 Clusters age: < 3-5 Myr cluster mass [M 50 20 Constrains on formation 10 time scale 5 3 Myr 1 Myr 0.1 0.2 0.3 0.5 0.7 1 1.5 2 3 4 65 cluster radius (pc) S. Pfalzner August 2018 HOW DO CLUSTERS DEVELOP AFTER FORMATION? Upp Cen-Crux • Full information over first 20 Myr only associations I Lac 1 Ori 1a Low Cen-Crux available for massive clusters Upp Sco IC 1805 Ori 1c 10 loose clusters NGC 7380 NGC 6611 Ori 1b • Two types of “clusters“: NGC 2244 CygOB2 RSGC03 each increases in size with age RSGC02 [pc] χ Per but along different tracks eff Quintuplett h Per r Embedded clusters DSB2003 RSGC01 1 Westerlund 1 • Loose clusters successors of the Westerlund 2 compact clusters NGC 3603 clusters investigated in embedded Trumpler 14 clusters Arches phase 1 10 Age [Myr] • Embedded clusters associations Pfalzner A&A 2009 Name convention: Portegies Zwart 2010 S. Pfalzner August 2018 NO INFORMATION HOW COMPACT CLUSTERS FORM Next big challenge: ? Cyg OB2 20000 NGC 3603 Westerlund 2 NGC 6611 How do massive Arches IC 1805 10000 compact clusters form? Trumpler 14 DBS 2003 NGC 2244 5000 NGC 7380 Ori 1b ] sun 2000 1000 ONC 500 200 cluster mass [M 100 50 20 10 0.2 0.3 0.5 0.7 1 1.5 2 3 4 65 cluster radius (pc) S. Pfalzner August 2018 CLUSTERS DYNAMICS AFTER FORMATION Clusters expand by factor 5-10 Little mass loss Upp Cen-Crux 5 I Lac 1 Ori 1a Low Cen-Crux Upp Sco IC 1805 Ori 1c 10 loose clusters Westerlund 1 NGC 7380 RSG 2 NGC 6611 4.5 Cyg OB2 NGC 6611 Ori 1b RSG 1 NGC 2244 CygOB2 ]) Arches Quintuplett RSGC03 sun IC 1805 h Per RSGC02 χ Per [pc] χ Per NGC 3603 eff Quintuplett h Per 4 Trumpler 14 r DSB2003 RSGC01 NGC 2244 Ori 1c NGC 7380 Westerlund 2 Westerlund 1 1 Ori 1b Ori 1a Westerlund 2 log (mass [M compact clusters Upp Sco UCL NGC 3603 3.5 I Lac 2 Trumpler 14 Arches LCC 3 1 10 1 2 5 10 20 Age [Myr] Age [Myr] Pfalzner A&A 2009 S. Pfalzner August 2018 ASSOCIATION DYNAMICS AFTER FORMATION Associationss expand by factor 5-10 Loose 80-90% of their mass Upp Cen-Crux 5 I Lac 1 Ori 1a Low Cen-Crux Upp Sco IC 1805 Ori 1c 10 loose clusters Westerlund 1 NGC 7380 RSG 2 NGC 6611 4.5 Cyg OB2 NGC 6611 Ori 1b RSG 1 NGC 2244 CygOB2 ]) Arches Quintuplett RSGC03 sun IC 1805 h Per RSGC02 χ Per [pc] χ Per NGC 3603 eff Quintuplett h Per 4 Trumpler 14 r DSB2003 RSGC01 NGC 2244 Ori 1c NGC 7380 Westerlund 2 Westerlund 1 1 Ori 1b Ori 1a Westerlund 2 log (mass [M compact clusters Upp Sco UCL NGC 3603 3.5 I Lac 2 Trumpler 14 Arches LCC 3 1 10 1 2 5 10 20 Age [Myr] Age [Myr] Pfalzner A&A 2009 S. Pfalzner August 2018 MODELS OF CLUSTER FORMATION • Distribution of subclusters that merge Increasing size with age not straightforward • Clusters form, no dynamics afterwards Increasing size with age not straightforwar • Formation as single entity Gas expulsion: explanation for cluster growth S. Pfalzner August 2018 NO SUBCLUSTER MERGING Kuhn et al. arXiv:1807.06085 No signs of subcluster merging S. Pfalzner August 2018 CLUSTER EXPANSION Kuhn et al. arXiv:1807.06085 Gaia 2DR Clusters Age range 1-5Myr Expansion speed: 1 km/s 1pc/Myr 75% of clusters show clear sign of cluster expansion S. Pfalzner August 2018 RESULT OF GAS EXPULSION DEPENDS ON .... • 20000 Star formation efficiency Tutukov 1978, Hills 1980, Mathieu 1980, Adams 80% 2000,Geyer & Burkert 2001, Kroupa et al. 2001, Boily 70% &Kroupa 2003, Bastian & Goodwin 2006, Converse 15000 ) & Stahler 2011 ... many more 60% sun • Remant cluster 10000 50% • Mass depends on SFE stellar mass(M 40% 5000 • 30% SFE : 10% of stars in remnant 30% 20% 0 0 5 10 15 10% 20 cluster time(Myr) Highly deterministic S. Pfalzner August 2018 ASSOCIATIONS/ EXTENDED CLUSTERS SeQuence 10000 corresponds to 40% SFE 30% SFE 10000 40% SFE 30% SFE Corresponds to 1000 maximum observed mass(Msun) SFE in solar 1000 mass(Msun) neighbourhood < 4Myr 4 Myr < t < 10Myr 20% SFE 10Myr < t < 20Myr 100 < 4Myr 4 Myr < t < 10Myr 20% SFE 10Myr5 < t < 20Myr 10 15 20 100 half-mass radius (pc) 5 10 15 20 half-mass radius (pc) S. Pfalzner August 2018 WHAT DRIVES MASSIVE CLUSTER EXPANSION? Upp Cen-Crux I Lac 1 Loose Clusters Ori 1a Low Cen-Crux Upp Sco IC 1805 Ori 1c 10 loose clusters Large mass loss, strong expansion NGC 7380 NGC 6611 Ori 1b NGC 2244 CygOB2 RSGC03 Gas expulsion ~30% SFE RSGC02 [pc] χ Per eff Quintuplett h Per r DSB2003 RSGC01 1 Westerlund 1 Westerlund 2 Compact clusters NGC 3603 compact clusters Trumpler 14 Arches Little mass loss, strong expansion 1 10 Stellar ejections > 60% SFE Age [Myr] S. Pfalzner August01.09.18 2018 GAS EXPULSION: SCHEMATIC PICTURE Bound Gas expulsion: Ramnant cluster embedded Mixture of bound and unbound stars system Bound and unbound separated bound unbound Gas expulsion Embedded cluster Random Two velocities, Two velocities, Random velocities velocities not spatially spatially distinguishable distinguishable No expansion Expansion No expansion S. Pfalzner August 2018 OBSERVATIONAL INDICATION FOR GAS EXPULSION SCENARIO A B A B Gaia-Eso Survey data of g Velorum cluster (Jeffries et al. 2014) Two populations well separated in space and velocity S. Pfalzner August 2018 OBSERVATIONS SHOW: Most stars form in stellar groups – either in associations or clusters – so far we only investigated those in associations – distinct mass-size relations exist Associations: • Gas expulsion driven expansion seems likely explanation • most stars unbound within 10 Myr • their remains a remnant cluster Clusters • survive because of their compactness, not their mass • we have no idea how they form S. Pfalzner August 2018.
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