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Star Clusters As Witnesses of the Evolutionary History of the Small Magellanic Cloud

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Star Clusters As Witnesses of the Evolutionary History of the Small Magellanic Cloud JENAM, Symposium 5: Star Clusters – Witnesses of Cosmic History Star Clusters as Witnesses of the Evolutionary History of the Small Magellanic Cloud Eva K. Grebel Astronomisches Rechen-Institut 11.0Z9.2e00n8 trum für AstrGroebnel,o JEmNAMie Sy mdp.e 5:r S MUC nStairv Celusrtesrsität Heidelbe0 rg My collaborators: ! PhD student Katharina Glatt ! PhD student Andrea Kayser (both University of Basel & University of Heidelberg) ! Andreas Koch (U Basel & UCLA / OCIW) ! Jay Gallagher, D. Harbeck (U Wisc) ! Elena Sabbi (U Heidelberg & STScI) ! Antonella Nota, Marco Sirianni (STScI) ! Monica Tosi, Gisella Clementini (U Bologna) ! Andrew Cole (U Tasmania) ! Gary Da Costa (ANU) 11.09.2008 Grebel, JENAM Symp. 5: SMC Star Clusters 1 NGC 416 (OGLE) Tracers of the Age-Metallicity Relation: ! Star clusters: ! Easily identifiable. ! Chronometers of intense star formation events. ! Single-age, single-metallicity fossils of local conditions. ! Star clusters in the SMC: ! Clusters formed (and survived) for most of its lifetime " Closely spaced set of age tracers! " Unique property of the SMC. # Milky Way: No comparable set of intermediate-age, populous clusters. # LMC: Age gap at intermediate ages. 11.09.2008 Grebel, JENAM Symp. 5: SMC Star Clusters 2 Cluster-based Age-Metallicity Relation: Photometry Spectroscopy After Da Costa 2002 An inhomogeneous sample: ! Photometric and spectroscopic metallicities from different techniques ! Photometric ages from ground-/space-based data of differing depth 11.09.2008 Grebel, JENAM Symp. 5: SMC Star Clusters 3 Getting Homogeneous Ages and Metallicities: PhD thesis Katharina Glatt ! HST / ACS program to obtain deep CMDs (PI: Gallagher) $ GO 10396, 29 orbits, executed 2005 – 2006. $ 6 populous intermediate-age clusters, 1 globular cluster: NGC 419, Lindsay 38, NGC 416, 339, Kron 3, Lindsay 1, NGC 121. In common w. Da Costa & Hatzidimitriou: Ln 1, Kr 3, NGC 339, 121. $ Several strategically chosen field regions. $ F555W, F814W; $ WFC (200” x 200”; 0.05”) & HRC (29” x 26”; 0.025”). ! Complements HST / ACS program for young SMC clusters $ PI: Nota, GO 10248; 10542. 11.09.2008 Grebel, JENAM Symp. 5: SMC Star Clusters 4 Getting Homogeneous Ages and Metallicities: PhD thesis Andrea Kayser ! ESO / VLT program for metallicities (PI: Grebel) $ 35 hours, executed 2004 – 2006. $ 12 populous intermediate-age clusters: Ln 11, Ln 116, Ln 32, Ln 38, Kr 28, Kr 44, NGC 152, NGC 339, NGC 361, NGC 411, NGC 416, NGC 419. In common with Da Costa & Hatzidimitriou: Ln 11, NGC 339. In common with HST / ACS: Ln 38, NGC 416, 419, 339. $ Adjacent field regions. $ FORS2 MXU (mass exchange unit), grism 1028x+29, OG590+32. $ R ~ 3,400, 773 – 948 nm (includes NIR Ca II triplet); S/N ~ 70. ! Complements ESO/VLT project for younger SMC clusters $ See paper by Parisi et al. 2008 (arXiv:0808.0018). 11.09.2008 Grebel, JENAM Symp. 5: SMC Star Clusters 5 Target Selection: Photometry Spectroscopy Our sample for spectroscopy Our sample for photometry L116 Da Costa et al. (2002) ! Spectroscopic metallicities for as many clusters with only photometry ! Deep CMDs for as many of the older clusters as possible ! As much of an age and metallicity coverage as possible ! As wide an area coverage as possible 11.09.2008 Grebel, JENAM Symp. 5: SMC Star Clusters 6 Target selection: Spatial distribution: Our spectroscopy targets Spectroscopic targets of Da Costa & Hatzidimitriou Some of the calibrating clusters Our photometry targets 11.09.2008 Grebel, JENAM Symp. 5: SMC Star Clusters 7 The Oldest Cluster in the SMC: NGC 121 ! Known to be the oldest star cluster in the SMC. ! Known to be the only globular cluster in the SMC. ! Suggested to be a few Gyr younger than the oldest GCs in the LMC, For, Sgr, Milky Way. 11.09.2008 Grebel, JENAM Symp. 5: SMC Star Clusters 8 The Oldest Cluster in the SMC: NGC 121 ! Padova & Teramo isochrones provide good fit of main sequence, subgiant branch, lower red giant branch. ! Do not reproduce slope of upper RGB correctly. ! Both yield relatively “young” ages; 11 – 12 Gyr. Glatt et al. 2008, AJ, 135, 1106. [Fe/H]spec = –1.46 dex 11.09.2008 Grebel, JENAM Symp. 5: SMC Star Clusters 9 The Oldest Cluster in the SMC: NGC 121 ! Dartmouth isochrones (Dotter et al. 2007) provide excellent fit of the entire CMD. ! Yields again a relatively young age. ! NGC 121 consistently younger by 2–3 Gyr than oldest known GCs. [Fe/H] = –1.46 dex Glatt et al. 2008, spec AJ, 135, 1106. 11.09.2008 Grebel, JENAM Symp. 5: SMC Star Clusters 10 Glatt et al. 2008, AJ, in press (astroph) Intermediate-Age Clusters in the SMC: Lindsay 1 Kron 3 NGC 339 NGC 416 Lindsay 38 NGC 419 11.09.2008 Grebel, JENAM Symp. 5: SMC Star Clusters 11 Glatt et al. 2008, AJ, in press (astroph) Intermediate-Age Clusters in the SMC: 7.5 Gyr 6.5 Gyr 6 Gyr ~ 1.3 Gyr 6 Gyr 6.5 Gyr 11.09.2008 Grebel, JENAM Symp. 5: SMC Star Clusters 12 Glatt et al. 2008, AJ, in press (arXiv:0807.3744) The special case of NGC 419: ! Padova isochrones approximate CMD best. ! No well-defined main-sequence turn-off. ! Possibly multiple turn-offs; age (range) uncertain. Glatt et al. 2008, AJ, in press (arXiv:0807.3744), and Sabbi et al., in prep. 11.09.2008 Grebel, JENAM Symp. 5: SMC Star Clusters 13 The Age-Metallicity Relation of the SMC 11.09.2008 Grebel, JENAM Symp. 5: SMC Star Clusters 14 Membership Criteria $ Radial Velocity " Only stars within 2! from the mean radial velocity $ Position in the CMD " Only stars on upper RGB $ Distance from the cluster center " Stars within R < 6 · Rcore $ Metallicity " Outliers discarded 11.09.2008 Grebel, JENAM Symp. 5: SMC Star Clusters 15 The Cluster Age-Metallicity Relation of the SMC VLT spectroscopy & ACS photometry of SMC clusters: Metallicity spread at a given age; SMC not well mixed! Parisi et al. 08 NGC 330 t al. 2008 e latt G t al. 2008, e Kayser 11.09.2008 Grebel, JENAM Symp. 5: SMC Star Clusters 16 The Cluster Age-Metallicity Relation of the SMC The AMR in comparison to models: Closed box; continuous SF, no infall or outflow of gas Bursting model w. three phases of different SFE (Pagel & Tautvaisiene 1998) Early burst (~ 13 Gyr), quiescent phase, recent burst (4 Gyr). n prep. i t al. 2008, e Kayser 11.09.2008 Grebel, JENAM Symp. 5: SMC Star Clusters 17 The Cluster Age-Metallicity Relation of the SMC “Inner” SMC clusters; “outer” SMC clusters: Little trend with age and metallicity. Kayser et al. 2008, in prep. 11.09.2008 Grebel, JENAM Symp. 5: SMC Star Clusters 18 The Cluster Age-Metallicity Relation of the SMC: ! No smooth age-metallicity relation. ! Metallicity spread at a given age; inhomogeneous enrichm. ! Mild radial trend. ! NGC 121 confirmed Parisi et al. 08 to be 2–3 Gyr younger NGC 330 than oldest GCs. ! Delayed GC formation? ! Dartmouth isochrones work very well for populations > 2 Gyr. ! Support for depth extent of SMC (at least 17 kpc from cluster distances) ! Multiple MSTO in NGC 419? ! Stay tuned for results on cluster MFs, structure, and field results. 11.09.2008 Grebel, JENAM Symp. 5: SMC Star Clusters 19.
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