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Stellar chemistries in dwarf Spheroidal galaxies and the Magellanic Clouds

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  1. Stellar chemistries in dwarf Spheroidal galaxies and the Magellanic Clouds Vanessa Hill • Stellar chemistries - chemical evolution: • Commonalities and peculiarities in dSph (and LMC) • Rôle of AGBs • Extremely low metallicity stars in dSph

  2. The standard picture (seminal) Matteucci & Brocato 1990

  3. Sculptor (m-M)0 = 19.7 Carina (m-M)0 = 20.0 B-R De Boer et al. 2010 and 2011 Cole et al. 07 Matteo priv com. Hildago et al. 09 Monelli et al. 09 Star formation histories B-R NOW Tolstoy, Hill & Tosi ARAA 2009

  4. Koch et al 2006, 2008 DART samples MV=-13.2 MV=-11.1 MV=-9.3 MV=-9.5

  5. Sculptor Fornax FLAMES Bar Disk Tolstoy et al. 2004, Battaglia et al. 2008 Battaglia et al. 2006 Venn et al. 2011, Lemasle et al. 2011 Battaglia et al. 2010 Tolstoy Hill Tosi 2009 DART DART DART DART Letarte et al. 2010 Lemasle et al. in prep (V-I) (V-I) LMC Van DerSwaelmen et al. 2013 & PhD: 160 * Sagittarius see talk by A. McWilliam Sgr:(Bellazzini et al. 2006) 12% old (>10Gyrs) >80% 5.5-9Gyrs ~6% younger stars (BP) Zaritsky

  6. Milky-Way Venn et al. 2004 The standard picture -elements SNII: [/Fe] ~0.4 (fast enrichment) SNIa:: Fe, no  (delayed enrichement) knee SNII +SNIa

  7. Distinct evolution SgrSbordone et al. 2007 + McWilliam et al. 2005 Milky-Way Venn et al. 2004 Tolstoy, Hill, Tosi 2009 ARAA

  8. SgrSbordone et al. 2007 + McWilliam et al. 2005 Fornax Letarte et al. 2010 Milky-Way Venn et al. 2004 Distinct evolution Tolstoy, Hill, Tosi 2009 ARAA

  9. SgrSbordone et al. 2007 + McWilliam et al. 2005 FornaxLetarte et al. 2010 Sculptor Tolstoy Hill Tosi 2009 & Hill et al. in prep) + Shetrone et al. 2003& Geisler et al. 2005 Milky-Way Venn et al. 2004 Distinct evolution • Each galaxy occupies a different locus - evolutionary track • [α/Fe] « knee » metallicity: according to the ability of the galaxy to retain metals • Sgr : [Fe/H]knee >-1.2 • Fnx: [Fe/H]knee <-1.5? (Lemasle et al. in preparation for an outer field cover nicely -1.0<[Fe/H]<-2.7 dex) • Scl: [Fe/H]knee ~ -1.8 • in accordance to total L of the galaxy • reflected on mean metallicity • linked to SFH (gas availablility?) SNII +SNIa Tolstoy, Hill, Tosi 2009 ARAA • Dispersion: none detected in Scl, Fnx, Sgr • Abundance pattern in the metal-poor stars everywhere undistinguishable ?->IMF

  10. LMC fieldPompeia, Hill et al. 2008, Van der Swaelmen, Hill et al. 2012 clustersHill et al. 2000, and 2009; Johnson et al. 2006; Mucciarelli et al. 2008, 2010 SMC clusterHill et al. in prep; **RR Lyrae starsHaschke et al. 2012 Milky-WayVenn et al. 2004 Distinct evolution • In the common metallicity regime, clusters and field stars agree. • alpha elements are depleted compared to the MW disk, as expected from: • slower SF (e.g. Matteucci & Brocato 1990, Pagel & Tautvaisiene1998) • Bursts of star formation (Wyse 1996, Pagel & Tautvaisiene1998) • Galactic winds (e.g. Freitas Pacheco 1998; Lehner 2007 evidence of outflow) • The position of the « knee » in [/Fe] is ill-defined, because of the lack of metal-poor field stars… • Old and metal-poor GCs resemble the galactic halo.No evidence for a different massive star IMF

  11. Is there truely a knee in Scl? MRS data: sorted by errors Kirby et al. 2010

  12. Is there truely a knee ? Texte MRS data: sorted by errors DART data Kirby et al. 2010

  13. There is a true plateau (and a knee) MRS data: sorted by errors DART data Low Z stars in Scl: Starkenburg et al. 2012 (Xshooter); Tafelmayer et al. 2010 (UVES) + 1 star Frebel et al. 2010 Kirby et al. 2010

  14. SgrSbordone et al. 2007 + McWilliam et al. 2005 Fornax Letarte et al. 2010 Sculptor Tolstoy Hill Tosi 2009 & Hill et al. in prep) + Shetrone et al. 2003& Geisler et al. 2005 SextansKirby et al. 2010 +Shetrone et al. 2003+Aoki et al 2009 Milky-Way Venn et al. 2004 Distinct evolution • Each galaxy occupies a different locus - evolutionary track • [α/Fe] « knee » metallicity: according to the ability of the galaxy to retain metals • Sgr: [Fe/H]knee >-1.2 • Fnx: [Fe/H]knee <-1.5? (Lemasle et al. in preparation for an outer field cover nicely -1.0<[Fe/H]<-2.7 dex) • Scl: [Fe/H]knee ~ -1.8 • Sextans: knee ????? • in accordance to total L of the galaxy (& mean metallicity) • Dispersion: probably present in Sextans (at all metallicities ?) -> inhomogeneous

  15. CarinaVenn et al. 2011, Lemasleetal. 2011 +Koch et al. 2008 + Shetrone et al. 2003 Milky-Way Venn et al. 2004 Distinct evolution • Each galaxy occupies a different locus - evolutionary track • [α/Fe] « knee » metallicity: according to the ability of the galaxy to retain metals • Sgr : [Fe/H]knee >-1.2 • Fnx: [Fe/H]knee <-1.5? • Scl: [Fe/H]knee ~ -1.8 • Carina: no knee, dispersion ! • in accordance to total L of the galaxy (& mean metallicity) • Dispersion: Detected in Carina -> bursty SFH + inhomogeneous • Probably present in Sextans (at all metallicities ?) -> inhomogeneous • At the lowest metallicities (EMPS), inhomogeneities or smooth as in MW halo ?

  16. Revaz, Jablonka (2009, 2012) Sph code • Nbody-Tree-SPH code with simple chemistry (Mg, Fe): cosmologically motivated initial conditions, isolated galaxies, feedback treated with care. • varying Mtot, ρg, rmax, c*, (εSN,tad) • reproduces L-metallicity and M/L-L relations

  17. ModellingScl in a cosmological contexte Romano & Starkenburg 2013

  18. Milky-Way Venn et al. 2004 knee SNII +SNIa r-process +SNIa +s-process r-process The standard picture -elements SNII: [/Fe] ~0.4 (fast enrichment) SNIa:: Fe, no  (delayed enrichement) Neutron-capture element R- process: massive stars (fast enrichment) S-process: AGB stars (slower enrichement)

  19. SgrSbordone et al. 2007, + McWilliam et al. 2005 FornaxLetarte et al. 2010 Sculptor Tolstoy Hill Tosi 2009 & Hill et al. in prep) + Shetrone et al. 2003& Geisler et al. 2005 Milky-Way Venn et al. 2008 N-capture elements LMC fieldVan der Swaelmen,Hill et al. 2012 clustersHill et al. 2000, and 2009; Johnson et al. 2006; Mucciarelli et al. 2008, 2010 **RR Lyrae starsHaschke et al. 2012 • 2nd peak r- and s- process elements (Ba, La, ..) similar to MW in Scl: • Dominated by r- process at the lowest metallicities (all galaxies) • Mix of r- and s- process [Fe/H]> -2 • In Fornax, Sgr and the LMC, thes-process displays a strong enhancement at the highest metallicities(younger ages): AGBs • s-processyields are metallicity-dependent (seeds), favoringhigh-A over low-Aelements (Ba/La over Y/Zr), and Y or Zr are observed not to beenhanced in Fnx/Sgr/LMC. • Points towardslow-metallicity AGB pollution • Models: Lanfranchi et al. (dSph); Tsujimoto & Bekki (LMC) • Shouldbeseen in Carbon ? r-ands- SS r- LMC

  20. SgrMcWilliamet al. 2005 FornaxLetarte et al. 2010 Sculptor Tolstoy Hill Tosi 2009 & Hill et al. in prep) + Shetrone et al. 2003& Geisler et al. 2005 Milky-Way Venn et al. 2008 Europium LMC fieldVan der Swaelmen,Hill et al. 2012 clustersHill et al. 2000, and 2009; Johnson et al. 2006; Mucciarelli et al. 2008, 2010 **RR Lyrae starsHaschke et al. 2012 • The “pure” r-process element Eu (>93% in the Sun): shouldbehavelike an elements • Eufollowsa as expected in Scl • On the contrary, Eu (and but [Eu/α]) issignificantly enhanced in the metal-rich part of Sgr,Fnxand the LMC,i.e. in the galaxies with also strong AGB contributions Tempting to suggest an AGB contribution to Eu…. (also CEPM-sr stars). But see A. McWilliam’s talk.

  21. Sculptor: bringing all together • Fitting wide field & deep CMD simultaneously with the MDF: • beats the age-metallicity degeneracies • overall fit of CMD (x2) not necessarily better, but builds a self-consistent picture T. de Boer et al. 2011(DART)

  22. Sculptor: bringing all together T. de Boer et al. 2011(DART)

  23. Sculptor: spatial variations T. de Boer et al. 2011(DART)

  24. Sculptor: spatial variations • Sculptor is not only case (Sextans: Battaglia et al. 2010, ...) • linked to environment ? (seems not to be seen in isolated dSph) • ! Caution when interpreting MDFs derived in the center only (bias towards younger, metal-rich) Tolstoy et al. 2004 Battaglia et al. 2008a, 2008b

  25. Sculptor: bringing all together • The SFH can conversely be used to constrain solutions to derive more robust ages on the RGB • The SNIa (knee) in Scl occurred 2Gyrs after the start of SF • Presumably no SNIa pollution will be observed in Scl outskirts (no data yet). T. de Boer et al. 2011 • A self-consistent model (reproducing SFH, chemical enrichment timescale) for the two populations (incl. kinematics) is yet to be produced. (e.g. Revaz & Jablonja 2011 could not reproduce population gradients)

  26. Quantifying the number of low-Z stars (Kirby 2008) Starkenburg et al. 2010 Starkenburg et al. 2010 • Calibrated to the low-Z regime, CaII triplet survey (DART) yields metallicities down to -4. • The shape of the low-Z tail is undistiguishable from that of the MW halo ([Fe/H]<-2.5)

  27. Low-Z tail: Characterising low-Z stars • Stars with [Fe/H]<<-3 confirmed in dSph • Their chemical composition are mostly similar to those of the MW halo • Hints of true dispersion • Low-Z follow-up ( ): • Subaru (Aoki et al. 2009) • VLT/UVES (Tafelmeyer et al. 2010: Fnx, Scl, Sext) • VLT/Xshooter (Starkenburg et al. in prep,Scl) • Magellan/MIKE (Venn et al. 2011 subm., Car) Shetrone et al. 2001, 2003 Koch et al. 2008, 2009 Cohen &Huang 2009 Frebel et al. 2009, 2010 Tolstoy, Hill, Tosi 2009

  28. Summary • Chemical evolution consistent with a less efficient enrichment (SN Ia contributions at lower Fe than in MW) • The position of the knee seems to correlate with the galaxy L or <[Fe/H]> or Mv • Expected if lowest mass systems loose easily their gas (less efficient enrichment) • When star formation is extremely low & bursty, dispersion may prevails at all metallicities (Carina?, Sextans?) • Very high s-process element content of the metal-rich populations in Fornax, Sagittarius and the LMC (but NOT in Sculptor, Carina, Draco), result from a strong pollution by metal-poor AGBs. • dSph do host some extremely metal poor stars (<-3), although in small numbers • Metal poor stars abundances are not (yet) very significantly different from those of the metal-poor halo (but see M. Shetrone’s talk about C) • Many modelling efforts ongoing….

  29. Summary • Star formation histories: the last 10 years have relied on a CDMs from shallow ground-based large-coverage surveys (e.g.Zaritskyet al. ) plus a few very deep CMD in tiny fields (HST, e.g. Dolphin et al. 2001). We have now entered an era of HST plus ground-based, very deep and large fovimaging (eg. Gallart et al. 2008, Noel et al. 2007, 2009). See talks by M. Cignoni, R. Carrera. • Metallicity distributions/age-metallicity relations: for a long time, clusters were the dominant probes. Large spectroscopic surveys are providing reliable metallicity distributions (from individual stars) in the field. Gradients are still an open issue.See talks by W. Hankey, R. Carrerra… • Detailed abundancesand chemical evolution: large samples of of stars in the LMC disk and bar (field and clusters) show: • LMC disk chemical evolution consistent with slower evolution (SN Iacontributes at lower Fe than in the MW disk) • Very abundant s-process elementstraced to a strong pollution by metal-poor AGBs. • Numerous nucleosyntheticpuzzles opened up…See talk of M. Van derSwaelmen • The metal-poor (and EMP) population remains elusive in current surveys • SMC remains essentially uncharted territory

  30. Manganese models: • different SFH: • Scl/Scl, Fnx/Fnx • without metallicity-dependent SNIa yields: • with metallicity-dependent SNIa yields: North et al. (DART) 2012

  31. 1- FromCMDs to SFHs Tolstoy, Hill, Tosi 2009 ARAA

  32. LMC ~50kpc SMC ~70kpc OGLE Zaritsky 3- Detailed elemental abundances • Present gas (HII regions) • Young population (<<1Gyr) V>12 (SGs, …) • Intermediate ages (1-10 Gyr) V>16-17 (AGBs, RGBs) • Old population ( >10Gyr) V>16 (RGBs), V>19 (RR Lyr)

  33. 7.5deg H I NIR (2MASS) LMC • Young populations: Irregular • Older populations: smooth • SFH, especially at young ages, will depend on field ! Zaritsky et al. 2004

  34. Cole et al. 2005 LMC Bar Bar Outer disk Carrera et al. 2008a Metallicity distribution: LMC LMC: • No strong gradient of RGBs along the disk • The bar may be slightly more metal-rich (-0.3 vs -0.5). • “halo” (similar to old GCs) present in all regions around [Fe/H]=-1.5. Similar to outer halo (Majevski 2009) ? Cole et al. 2009

  35. Metal-poor stars ? • Random RGB stars samples in bothcloudsfail to sampleproperly the metal-poortails (if any). • RR Lyrae select old (and presumablymetal-poor stars) Haschke et al. 2012 (OGLE III RRLyr) LMC SMC

  36. Carrera 2008b Age-metallicityrelations SMC LMC Cole et al. 2005 Carrera 2008a

  37. Age-metallicity relations SMC LMC Sharma et al. 2010 Parisi et al. 2009

  38. LMC fieldPompeia, Hill et al. 2008, Van der Swaelmen,Hill et al. 2012 clustersHill et al. 2000, and 2009; Johnson et al. 2006; Mucciarelli et al. 2008, 2010 SMC clusterHill et al. in prep; **RR Lyrae starsHaschke et al. 2012 Milky-WayVenn et al. 2004 N-capture elements • s-processvery efficient in LMC disk, with a take off around [Fe/H]>-1.0 • s-processyields are metallicity-dependent (seeds), favoringhigh-A over low-Aelements (Ba over Y). • Points towardslow-metallicity AGB pollution • r- to s- transition canbeused as clock (delayed AGB products): around [Fe/H]=-1.0dex • LMC AMR implies ~10 Gyrsatthismetallicity • First cluster to show s-processis 9Gyrs old r-ands- r-ands- Pure r-

  39. LMC fieldPompeia, Hill et al. 2008, Van der Swaelmen, Hill et al. 2012 clustersHill et al. 2000 and 2009; Johnson et al. 2006; Mucciarelli et al. 2008, 2010 SMC clusterHill et al. in prep; **RR Lyrae starsHaschke et al. 2012 Milky-WayVenn et al. 2004 N-capture elements • r process: should behave like an elements. On the contrary, Eu is enhanced in the LMC (and SMC) compared to the MW disk. (already known in supergiants, Russell&Bessell 1989, Luck & Lambert 1992, Hill et al. 1995, 1999, Luck et al. 1998) • s- process very efficient in LMC disk, with a take off around [Fe/H]>-1.0 • s-process yields are metallicity-dependent (seeds), favoring high-A over low-A elements (Ba over Y). • Points towards low-metallicity AGB pollution • r- to s- transition can be used as clock (delayed AGB products): around [Fe/H]=-1.0dex • LMC AMR implies ~10 Gyrs at this metallicity • First cluster to show s-process is 9Gyrs old r- process r- process

  40. LMC fieldPompeia, Hill et al. 2008, Van der Swaelmen, Hill et al. 2012 clustersHill et al. 2000, and 2009; Johnson et al. 2006; Mucciarelli et al. 2008, 2010 SMC clusterHill et al. in prep; **RR Lyrae starsHaschke et al. 2012 Milky-WayVenn et al. 2004 Distinct evolution • In the common metallicity regime, clusters and field stars agree. • alpha elements are depleted compared to the MW disk, as expected from: • slower SF (e.g. Matteucci & Brocato 1990, Pagel & Tautvaisiene1998) • Bursts of star formation (Wyse 1996, Pagel & Tautvaisiene1998) • Galactic winds (e.g. Freitas Pacheco 1998; Lehner 2007 evidence of outflow) • The position of the « knee » in [/Fe] is not very defined, even in the LMC: lack of metal-poor field stars… This hampers a proper timing of the early chemical enrichment. • Old and metal-poor GCs resemble the galactic halo. Field stars statistics are exceedingly low… No evidence for a different massive star IMF

  41. LMC fieldPompeia, Hill et al. 2008, Van der Swaelmen,Hill et al. 2012 clustersHill et al. 2000, and 2009; Johnson et al. 2006; Mucciarelli et al. 2008, 2010 SMC clusterHill et al. in prep; **RR Lyrae starsHaschke et al. 2012 Milky-WayVenn et al. 2004 N-capture elements • r process: shouldbehavelike an elements. On the contrary, Eu isenhanced in the LMC (and SMC) compared to the MW disk. (alreadyknown in supergiants, Russell&Bessell 1989, Luck & Lambert 1992, Hill et al. 1995, 1999, Luck et al. 1998) • s-processvery efficient in LMC disk, with a take off around [Fe/H]>-1.0 • s-processyields are metallicity-dependent (seeds), favoringhigh-A over low-Aelements (Ba over Y). • Points towardslow-metallicity AGB pollution • r- to s- transition canbeused as clock (delayed AGB products): around [Fe/H]=-1.0dex • LMC AMR implies ~10 Gyrsatthismetallicity • First cluster to show s-processis 9Gyrs old r-ands- r-ands- Pure r-

  42. LMC Pompeia, Hill et al. 2008 SgrSbordone et al. 2007 FornaxLetarte et al. 2010 Milky-WayVenn et al. 2008 Similarities withinthe local group… • LMC, Sgr, Fornax: extremely similar chemical peculiarities (, odd elements, iron peak, s- process) • Dominated by intermediate-age population • Totally different gaz content, ongoing star formation • …different orbits… Sgr most tidally disturbed, Fnx less, LMC even less (more massive) • What about the SMC ?

  43. LMC Pompeia, Hill et al. 2008 SgrSbordone et al. 2007 FornaxLetartePhD 2007 SculptorTolstoy Hill Tosi 2009 & Hill et al. in prep Milky-WayVenn et al. 2008 … and distinct evolution • Scl: dominated by an old population • Does not show enhanced s- process • Nor the other pecularities: low Ni, low Na.