Chemical Abundances, Dwarf Spheroidals and Tidal Streams

1. Chemical Abundances, Dwarf Spheroidals and Tidal Streams Steven Majewski (University of Virginia) Principal Collaborators: Mei-Yin Chou (UVa - Ph.D. thesis), Katia Cunha, Verne Smith (NOAO), David Martínez-Delgado (IAC), David Law (UCLA), Jeffrey Carlin (UVa - Ph.D. thesis), Ricardo Munoz (Yale) Image credit: David Law & SRM

2. Topics Discussed: • Some Motivations to Study Chemistry of Tidal Streams • Connection between dSphs and stars in the MW halo. • Reconstruct chemical distribution of original satellite galaxies. • Learn about SFHs, chemical enrichment histories, accretion histories. • Chemical fingerprinting stars to their parent source. • 2. Case Study: MDF Variation along the Sgr Stream • Find a strong metallicity gradient along the Sgr tidal tail. • Shows that Sgr originally had significant radial metallicity gradient. • 3. Case Study: Chemical Patterns in the Sgr System • Find relativechemical evolution/SFH between Sgr, MW & other satellites. • Use distinctive patterns to fingerprint other Sgr stars in Galactic halo. • 4. Case Study: Fingerprinting the Tri-And Star Cloud • Testing the connection to the Monoceros stream. • 5. The Future with New Surveys: Comments about APOGEE

3. Hierarchical Formation of Halos Today ~1 stream with • < 30 mag/arcsec2 attached to still-bound satellite should be visible per MW-like galaxy.(Johnston et al., in prep.) Font et al. (2006)

4. Prominent Tidal Streams around Disk Galaxies NGC 4013 Milky Way NGC 5907 Sgr Model (Law et al. 2005) Martinez-Delgado, Gabany et al. (2008, 2009)

5. Chemical HistoriesDistinctive abundance patterns-- [α/Fe], s-process (Y, La, etc.)-- reflect the unique chemical historyof the parent system, e.g., [α/Fe] (Ti, Mg, O, etc.) indicates the Type II/Type Ia SNe ratio of the parent system From McWilliam (1997)

6. HaloThick diskThin disk Chemical Histories:The MW Halo / dSph (Dis?)Connection dSph stars 1) dSphs appear to differ from MW halo (and even from each other) 2) Chemical fingerprinting (e.g., Freeman & Bland-Hawthorn 2002 - “tagging”) may possibly connect field stars to dSph progenitors Compilation from Venn et al. (2004)

7. Explaining the Halo/dSph Chemical Dichotomy Font et al. (2006), Robertson et al. (2005): Bulk of halo from massive, Magellanic Cloud-sized accreted early on, when chemistry dominated by SNII.

8. Explaining the Halo/dSph Chemical Dichotomy Majewski et al. (2002), Munoz et al. (2006, 2008): Satellites with prolonged chemical evolution and tidal disruption naturally leads to evolution in types of stars contributed to MW halo.

9. Chemical Study of the Sgr dSph + Tidal Stream • Results in Chou et al. 2007, ApJ, 670, 346, Chou et al. 2009 (~submitted), • High resolution, high S/N (50-200) • spectroscopy of 2MASS-selected • M giants in Sgr and its stream. • 31 stars from KPNO 4-m (R~ 35000) • 12 stars from TNG 3.5-m (R~ 45000) • 16 stars from Magellan 6.5-m (R~ 19000) • Use of predominantly northern telescopes leads • to focus on the leading arm.

10. R~ 35000 Derivation of Abundances: MOOG (Sneden 1973): An LTE Stellar Line Analysis Program Ti Ti - Teff from J-K (Houdashelt et al. 2000) - log g from isochrone (Girardi et al. 2000) - Initial metallicity guess EW measurements Model Atmosphere Line List log g MOOG log Teff [Fe/H] and [x/Fe] If the output [Fe/H] not consistent

11. The expected dynamical age of debris along the tidal stream: Stars lost from Sgr: 1 orbit ago; ~0.5 Gyr 2 orbits ago; ~1.4 Gyr 3 orbits ago; ~2.2 Gyr 4 orbits ago; ~3.1 Gyr 1 radial period ~ 0.85 Gyr Model (Law et al. 2005)

12. Sgr Leading Arms and an NGP Moving Group Brightest stars (K< 10) in: Sgr core Leading arm north(lost ~ 2 Gyrs ago) Leading arm south (lost ~ 3 Gyrs ago) Also, peculiar group of ‘NGP’ M giant stars having radial velocities different from the main leading arm trend

13. Iron Abundance Analysis: • 11 Fe I lines in a narrow spectral window ~ 7440-7590 Å • (Smith & Lambert 1985, 1986, 1990) • LTE code MOOG • combined with a • Kurucz ATLAS9 (1994) • solar model • Solar gf-values of • Fe I lines R ~ 35000 R ~ 45000 R ~ 19000

14. Strong Metallicity Gradient along the tidal tail! Chemical differences between the core and the tails! (Chou et al. 2007, ApJ, 670, 346) -0.4 • Time dependence in the chemistryof stars contributed to halo. • No MW dSph shows a metallicitygradient this strong -- e.g., largestis 0.5 dex variation across Sculptor (Tolstoy et al. 2004) • Either Sgr lost mass over a smallradial range with enormous gradient……or suffered a catastrophic loss withstars lost over a more normal gradient. -0.7 -1.2 -1.0 Median [Fe/H] of NGP group is similar to Sgr leading arm south

15. Reconstructed MDF of Sgr core several Gyrs ago • Relatively flat, more • metal-poor than • presently in the • Sgr core • The observed • chemical properties • of the presently • surviving satellites • may depend on • their tidal stripping • history MDF of Sgr core MDF of Sgr core MDF of Sgr tails MDF of Sgr tails Sum

16. Chemical Distributions in Sgr Stream [Ti/Fe] vs. [Fe/H] [Fe/H] Crosses are MW stars from Gratton, R. G. & Sneden, C. (1994),Fulbright, J. P. (2002), Johnson, J. (2002), and Reddy, B. E. et al. (2003) Triangles are dSph stars from Shetrone et al. (2001 & 2003), Geisler et al. (2005), Sadakane et al. (2004) Sgr resembles LMC more than other dSphs LMC stars from Pompéia et al. (2008)

17. Chemical Distributions in Sgr Stream [Y/Fe] vs. [Fe/H] YII Sgr resembles LMC more than other dSphs

18. La II line affected by hyperfine splitting Chemical Distributions in Sgr Stream [La/Fe] vs. [Fe/H] Here Sgr differs a little from LMC

19. Chemical Distributions in Sgr Stream [La/Y] vs. [Fe/H] – metal-poor AGB produce high [hs / ls], means slower SFR than MW • Sgr resembles LMC • Sgr evolved faster than dSph, slower than MW

20. Similar Enrichment, Different Timescales Clear SFR difference among dSphs, LMC and Sgr Hypothetical differences in chemical history +1 dex dSphs +0.5 dex LMC

21. SFR differs in Galactic satellites A “universal” enrichment historyvarying only by rate?? Hypothetical differences in chemical history +1 dex dSphs SFR slow to fast: dSphs  LMC  Sgr MW +0.5 dex LMC

22. Chemical Fingerprinting: • What is the peculiar NGP • group? • [Fe/H] ~ -1, similar to • Sgr leading arm south • (dynamical age ~ 3 Gyrs) • [Ti/Fe], [Y/Fe], [La/Fe] • and [La/Y] resemble • Sgr leading arm south Suggests NGP stars are Sgr stars of same dynamical age as leading arm south, but dynamics wrong for leading arm Proposed solution: NGP groupare Sgr trailing arm stars overlapping with Sgr leading arm north

23. Future Work on Sagittarius • Metallicity gradient and chemical trends along the Sgr • trailing arm • Longer, and stars stripped at specific epoch can be more cleanly isolated. • Gemini Phoenix (R~40k) H-band spectra Model (Law et al. 2005) 7+2 in these regions 10 stars in each region from Gemini South

24. Note that dynamically oldest of the Sgrstream stars are -enhanced -- but contributed within past few Gyr

25. Explaining the Halo/dSph Chemical Dichotomy Font et al. (2006): Satellites accreted >9 Gyr ago all destroyed, surviving satellites only recently accreted --> implies not major contributorsSgr exceptionary case? (e.g., only dSph presently in inner halo)

26. But Carina dSph is also contributing stars today… … undoubtedly some with-enhancement. Munoz et al. (2007, in prep.) Carina Koch et al. (2008)

27. Slide removed (Work In Progress)

28. Slide removed (Work In Progress)

29. Slide removed (Work In Progress)

30. The Apache Point Observatory Galactic Evolution Experiment (APOGEE) APOGEE at a Glance • Bright time 2011-Q2 to 2014-Q2, co-observing with MARVELS • 300 fiber, R ~ 24,000 cryogenic spectrograph • H-band window (1.51-1.68) • Minimum S/N = 100 • Typical RV uncertainty < 0.5 km/s • 0.1 dex precision abundances for ~15 chemical elements • ~105, 2MASS-selected, giant stars probing all Galactic populations

31. Expected elements and S/N tests @ R=21k and 0.1 dex precision • precision will degrade for lower S/N • S/N=100 for faintest star in plugboard, higher S/N for brighter stars Element SNR/pix SNR/pix SNR/pix [Fe/H]=-2 [Fe/H]=-1 [Fe/H]=0 Na 2673.7 309.8 56.0 S 1067.2 167.2 104.8 V 1504.7 164.4 42.4 K 505.6 75.3 44.6 Mn 184.9 50.9 46.9 Ni 101.6 45.7 46.4 Ca 89.5 42.7 41.0 Al 47.2 41.8 42.1 Si 35.2 38.6 35.7 N 147.3 41.7 21.4 Ti 110.0 36.5 38.9 Mg 33.1 36.7 26.4 Fe 41.6 34.3 21.3 C 40.4 14.8 8.3 O 24.5 14.6 9.1 ”Must have” element “Important to have/very desirable” element “Nice to have” element (also not shown Cr, Co)

32. The Promise of Detailed Chemical Abundance Studies The Initial Mass Function [(Si+Ca) / Fe] [(Mg+Ti) / Fe] • Relative abundances of different a elements reflects mass of SN progenitors: • Probes IMF • (e.g., McWilliam & Rich 1997 differences in a elements for bulge --- on right, above)

33. MARVELS Coordination - APOGEE use of 30 hr fields Solar metallicity RGB tip star: int (hr) HlimAVd(kpc) 3 12.5 5 27 10 13.4 10 27 30 14.1 15 26 [Fe/H]= -1.5 RGB tip star: int (hr) Hlim AVd(kpc) 3 12.5 0 40 10 13.4 0 60 30 14.1 0 83

34. Summary: • Sgr Stream shows strong metallicity gradient • Sgr originally had strong to very strong radial metallicity gradient. • Recent tidal stripping released stars, producing observed gradient in tails. • Sgr core of today differs from Sgr core of “yester-Gyrs”. • Sgr recently contributed -enhanced, metal-poor stars to MW; possibly other dSphs as well (e.g., Carina). • Overall, abundance patterns along the stream are • distinct from the dSphs and MW, similar to LMC •  SFR differences: dSphs  LMC  Sgr  MW • (slower faster) • Application of chemical fingerprinting demonstrated. • Tri-And Star Cloud not chemically linked to Monoceros. • APOGEE will access ~10-15 chemical elements in streams.