Stellar chemistries in dwarf spheroidal galaxies and the magellanic clouds
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Stellar chemistries in dwarf Spheroidal galaxies and the Magellanic Clouds. Vanessa Hill. Stellar chemistries - chemical evolution: Commonalities and peculiarities in dSph (and LMC) R ôl e of AGBs Extremely low metallicity stars in dSph. The standard picture (seminal).

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Stellar chemistries in dwarf Spheroidal galaxies and the Magellanic Clouds

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Stellar chemistries in dwarf spheroidal galaxies and the magellanic clouds

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


The standard picture seminal

The standard picture (seminal)

Matteucci & Brocato 1990


Star formation histories

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


Dart samples

Koch et al 2006, 2008

DART samples

MV=-13.2

MV=-11.1

MV=-9.3

MV=-9.5


Stellar chemistries in dwarf spheroidal galaxies and the magellanic clouds

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


The standard picture

Milky-Way Venn et al. 2004

The standard picture

-elements

SNII: [/Fe] ~0.4 (fast enrichment)

SNIa:: Fe, no  (delayed enrichement)

knee

SNII

+SNIa


Stellar chemistries in dwarf spheroidal galaxies and the magellanic clouds

Distinct evolution

SgrSbordone et al. 2007

+ McWilliam et al. 2005

Milky-Way Venn et al. 2004

Tolstoy, Hill, Tosi 2009 ARAA


Distinct evolution

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


Distinct evolution1

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


Distinct evolution2

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


Is there truely a knee in scl

Is there truely a knee in Scl?

MRS data: sorted by errors

Kirby et al. 2010


Is there truely a knee

Is there truely a knee ?

Texte

MRS data: sorted by errors

DART data

Kirby et al. 2010


There is a true plateau and a knee

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


Distinct evolution3

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


Distinct evolution4

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 ?


  • Sph code

    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


    Modelling scl in a cosmological contexte

    ModellingScl in a cosmological contexte

    Romano & Starkenburg 2013


    The standard picture1

    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)


    N capture elements

    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


    Europium

    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.


    Sculptor bringing all together

    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)


    Sculptor bringing all together1

    Sculptor: bringing all together

    T. de Boer et al. 2011(DART)


    Sculptor spatial variations

    Sculptor: spatial variations

    T. de Boer et al. 2011(DART)


    Sculptor spatial variations1

    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


    Sculptor bringing all together2

    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)


    Quantifying the number of low z stars

    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)


    Low z tail characterising low z stars

    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


    Stellar chemistries in dwarf spheroidal galaxies and the magellanic clouds

    • 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….


    Stellar chemistries in dwarf spheroidal galaxies and the magellanic clouds

    • 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


    Manganese

    Manganese

    models:

    • different SFH:

      • Scl/Scl, Fnx/Fnx

    • without metallicity-dependent SNIa yields:

    • with metallicity-dependent SNIa yields:

    North et al. (DART) 2012


    1 from cmds to sfhs

    1- FromCMDs to SFHs

    Tolstoy, Hill, Tosi 2009 ARAA


    3 detailed elemental abundances

    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)


    Stellar chemistries in dwarf spheroidal galaxies and the magellanic clouds

    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


    Metallicity distribution lmc

    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


    Metal poor stars

    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


    Age metallicity relations

    Carrera 2008b

    Age-metallicityrelations

    SMC

    LMC

    Cole et al. 2005

    Carrera 2008a


    Age metallicity relations1

    Age-metallicity relations

    SMC

    LMC

    Sharma et al. 2010

    Parisi et al. 2009


    N capture elements1

    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-


    N capture elements2

    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


    Distinct evolution5

    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


    N capture elements3

    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-


    Similarities within the local group

    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 ?


    And distinct evolution

    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.


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