Stellar chemistries in dwarf Spheroidal galaxies and the Magellanic Clouds

Stellar chemistries in dwarf Spheroidal galaxies and the Magellanic Clouds

Vanessa Hill

1. Stellar chemistries - chemical evolution:

1. Commonalities and peculiarities in dSph (and LMC)

2. Rôle of AGBs

3. Extremely low metallicity stars in dSph

The standard picture (seminal)

Matteucci & Brocato 1990

Star formation histories

Tolstoy, Hill & Tosi ARAA 2009NOW

B-RB-R

Sculptor(m-M)0 = 19.7

Carina(m-M)0 = 20.0

Monelli et al. 09 Hildago et al. 09 Cole et al. 07Matteo priv com.De Boer et al. 2010 and 2011

DART samplesMV=-11.1 MV=-13.2

MV=-9.3 MV=-9.5

Koch et al 2006, 2008

Sculptor Fornax

(V-I) (V-I)

Zaritsky

LMC

Bar Disk

Sgr: (Bellazzini et al. 2006)12% old (>10Gyrs)>80% 5.5-9Gyrs~6% younger stars (BP)

Sagittarius

Tolstoy et al. 2004, Battaglia et al. 2008 Battaglia et al. 2006

DART DART

FLAMES

Letarte et al. 2010

Lemasle et al. in prep

Tolstoy Hill Tosi 2009

DARTDART

Venn et al. 2011, Lemasle et al. 2011

Battaglia et al. 2010

see talk by A. McWilliam

Van Der Swaelmen et al. 2013 & PhD: 160 *

The standard picture-elements

SNII: [/Fe] ~0.4 (fast enrichment)

SNIa:: Fe, no (delayed enrichement)

Milky-Way Venn et al. 2004

SNII +SNIa

knee

Tolstoy, Hill, Tosi 2009 ARAA

Sgr Sbordone et al. 2007+ McWilliam et al. 2005

Milky-Way Venn et al. 2004 Distinct evolution

Distinct evolution



Fornax Letarte et al. 2010


Distinct evolution• Each galaxy occupies a different

locus - evolutionary track• [/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?) Dispersion: none detected in Scl, Fnx, Sgr

Abundance pattern in the metal-poor stars everywhere undistinguishable ? -> IMF



Fornax Letarte et al. 2010Sculptor Tolstoy Hill Tosi 2009 & Hill et al. in prep) + Shetrone et al. 2003& Geisler et al. 2005


SNII +SNIa

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

LMC field Pompeia, Hill et al. 2008, Van der Swaelmen, Hill et al.

2012 clusters Hill et al. 2000, and 2009;

Johnson et al. 2006; Mucciarelli et al. 2008, 2010

SMC cluster Hill et al. in prep;* * RR Lyrae stars Haschke et al. 2012Milky-Way Venn et al. 2004

Is there truely a knee in Scl ?

Kirby et al. 2010

MRS data: sorted by errors

Is there truely a knee ?

Kirby et al. 2010

MRS data: sorted by errors

Texte

DART data

There is a true plateau (and a knee)

Kirby et al. 2010

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

Distinct evolution

Dispersion: probably present in Sextans (at all metallicities ?) -> inhomogeneous


Fornax Letarte et al. 2010Sculptor Tolstoy Hill Tosi 2009 & Hill et al. in prep) + Shetrone et al. 2003& Geisler et al. 2005Sextans Kirby et al. 2010 +Shetrone et al. 2003+Aoki et al 2009Milky-Way Venn et al. 2004 Each galaxy occupies a different

locus - evolutionary track [/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)

Distinct evolution

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 ?

Carina Venn et al. 2011, Lemasle etal. 2011 +Koch et al. 2008 + Shetrone et al. 2003Milky-Way Venn et al. 2004

Each galaxy occupies a different locus - evolutionary track

[/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)

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

Revaz, Jablonka (2009, 2012)

Modelling Scl in a cosmological contexte

Romano & Starkenburg 2013

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)


SNII +SNIa

r-process +s-process

knee

r-process +SNIa

N-capture elements• 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, the s-process displays a strong enhancement at the highest metallicities (younger ages): AGBs

• s-process yields are metallicity-dependent (seeds), favoring high-A over low-A elements (Ba/La over Y/Zr), and Y or Zr are observed not to be enhanced in Fnx/Sgr/LMC.

Points towards low-metallicity AGB pollution

Models: Lanfranchi et al. (dSph); Tsujimoto & Bekki (LMC)

Should be seen in Carbon ?

r- and s-

Sgr Sbordone et al. 2007, + McWilliam et al. 2005

Fornax Letarte et al. 2010Sculptor Tolstoy Hill Tosi 2009 & Hill et al. in prep) + Shetrone et al. 2003& Geisler et al. 2005


SS r-

LMC

LMC field Van der Swaelmen, Hill et al. 2012

clusters Hill et al. 2000, and 2009;Johnson et al. 2006; Mucciarelli et al. 2008, 2010

* * RR Lyrae stars Haschke et al. 2012

Europium• The “pure” r-process element Eu

(>93% in the Sun): should behave like an elements

• Eu follows as expected in Scl• On the contrary, Eu (and but

[Eu/]) is significantly enhanced in the metal-rich part of Sgr, Fnx and 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.

Sgr McWilliam et al. 2005Fornax Letarte et al. 2010Sculptor Tolstoy Hill Tosi 2009 & Hill et al. in prep) + Shetrone et al. 2003& Geisler et al. 2005Milky-Way Venn et al. 2008

LMC field Van der Swaelmen, Hill et al. 2012

clusters Hill et al. 2000, and 2009;Johnson et al. 2006; Mucciarelli et al. 2008, 2010

* * RR Lyrae stars Haschke et al. 2012

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 together


Sculptor: spatial variations


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 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).

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)

T. de Boer et al. 2011

Quantifying the number of low-Z stars

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)

(Kirby 2008)

Starkenburg et al. 2010 Starkenburg et al. 2010

Low-Z tail: Characterising low-Z stars

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)

Stars with [Fe/H]<<-3 confirmed in dSph

Their chemical composition are mostly similar to those of the MW halo

Hints of true dispersion

Shetrone et al. 2001, 2003Koch et al. 2008, 2009Cohen &Huang 2009Frebel et al. 2009, 2010Tolstoy, Hill, Tosi 2009

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….

Summary1. Star formation histories: the last 10 years have relied on a CDMs from shallow

ground-based large-coverage surveys (e.g. Zaritsky et 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 fov imaging (eg. Gallart et al. 2008, Noel et al. 2007, 2009). See talks by M. Cignoni, R. Carrera.

2. 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…

3. Detailed abundances and chemical evolution: large samples of of stars in the LMC disk and bar (field and clusters) show:a. LMC disk chemical evolution consistent with slower evolution (SN Ia contributes at

lower Fe than in the MW disk)b. Very abundant s-process elements traced to a strong pollution by metal-poor AGBs.c. Numerous nucleosynthetic puzzles opened up…See talk of M. Van der Swaelmend. The metal-poor (and EMP) population remains elusive in current surveyse. SMC remains essentially uncharted territory

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


3- Detailed elemental abundances

Zaritsky

LMC~50kpc

OGLE

SMC~70kpc

• 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)

LMC

NIR (2MASS)

H I

7.5deg

Zaritsky et al. 2004

• Young populations: Irregular• Older populations: smooth

SFH, especially at young ages, will depend on field !

Metallicity distribution: LMCBar

Outer disk

Carrera et al. 2008a

Cole et al. 2005 LMC Bar

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 ?• Random RGB stars samples in both clouds fail to sample

properly the metal-poor tails (if any). • RR Lyrae select old (and presumably metal-poor stars)

LMC SMC

Haschke et al. 2012(OGLE III RRLyr)

Carrera 2008b

Age-metallicity relationsLMC SMC

Cole et al. 2005Carrera 2008a

Age-metallicity relations

Sharma et al. 2010 Parisi et al. 2009

SMCLMC

N-capture elements

r- and s-

Pure r-

r- and s-




SMC cluster Hill et al. in prep;* * RR Lyrae stars Haschke et al. 2012Milky-Way Venn et al. 2004 • 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).


• 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

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-





First cluster to show s-process is 9Gyrs old r- process


2012 clusters Hill et al. 2000 and 2009;



r- process

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 elements

r- and s-

Pure r-

r- and s-




SMC cluster Hill et al. in prep;* * RR Lyrae stars Haschke et al. 2012Milky-Way Venn et al. 2004 • 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-





First cluster to show s-process is 9Gyrs old

LMC Pompeia, Hill et al. 2008Sgr Sbordone et al. 2007Fornax Letarte et al. 2010


Similarities within the 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 ?

LMC Pompeia, Hill et al. 2008Sgr Sbordone et al. 2007Fornax Letarte PhD 2007Sculptor Tolstoy Hill Tosi 2009 & Hill et al. in prep


… and distinct evolution

• Scl: dominated by an old population

• Does not show enhanced s- process

• Nor the other pecularities: low Ni, low Na.

Stellar chemistries in dwarf Spheroidal galaxies and the Magellanic Clouds

Documents

Transcript of Stellar chemistries in dwarf Spheroidal galaxies and the Magellanic Clouds