a method for obtaining detailed abundances of extragalactic globular clusters

A Method for ObtainingDetailed Abundances of Extragalactic Globular Clusters

w/ Andy McWilliam (Carnegie Obs.)Scott Cameron, Janet Collucci (UM)

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MW- 47Tuc NGC 5128LMC- NGC 2005

Galaxy #1, Milky Way:

Formation: halo bulge/thick disk thin disk Evidence: abundances (Fe,O,Mg,Eu…) & kinematics (bulk, streams)

(1) Stars : *timescales*, substructure (recent: Ivans et al 2003)

The goal: formation histories of galaxies

halo thick bulge thin

Prochaska et al 2004 Yanny et al 2003

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Galaxy #1, Milky Way:

Formation: halo bulge/thick disk thin disk Evidence: abundances & kinematics

(2) Globular clusters: easy targets! date-able! old!

The goal: formation histories of galaxies

Parmentier et al 2000

Formation history of other galaxies:

Local Group: getting details (limitation: flux)

Evidence:

Supergiants (Venn et al 04, McWilliam & Smecker-Hanes 04) bright = young! (no history)

Venn et al 2004


Beyond…: different tools (limitation: flux & resolution)

Evidence: integrated light

- broad-band colors + [stellar population models] general: red (old/metal-rich) blue (young/metal-

poor)

- line indices + [stellar population models] Lick System (Worthey et al, Trager et al, Gonzalez et al), Rose


Worthy 1998

Age

Z

blueBeyond:

low resolution spectra (>2Å) + stellar population models

Limitations:

1- Age/metallicity degenerate (young/z-rich old/z-poor)

2- z vs Fe ? Mg, O,Ca…? calibration: abundances ratios?

* multiple generations of star formation.

Formation history of other galaxies :

Forbes et al. 04

Age

Z

Beyond:

low resolution spectra (>2Å) + stellar population models

Limitations:

1- Age/metallicity degenerate (young/z-rich old/z-poor)

2- z vs Fe ? Mg,O,Ca…? calibration: abundances ratios?

Recent: Principle component analysis:

PC1 metallicityStrader,Brodie ’04,Burstein et al 04

Globular clusters*

Formation history of other galaxies :

Forbes et al. 04

Beyond: integrated light of GCs

Principle component analysis: PC1 metallicityForbes et al.’04, Strader,Brodie ’04, Burstein et al 04

• [Fe/H] ( or z): 0.1 dex (optimistic?)

• Age: 3 Gyrs

• [E/Fe]: 0.1-0.2 (?) (“” or “enhanced”) C,N; O,Mg,Si,Ca; Cr; Na produced in SNII, SNI, and AGB stars

Missing: z vs. Fe vs. , self-enrichment, IMF

**M31: young (0.5-5Gyr), disk GC system (Beasley 04, Burstein 04, Morrison 04)

Why high resolution?

[Fe/H] -1

Perrett et al 2002, M31

Globular cluster spectra:

5.1 Å

0.17 Å

Mg2 Mgb

Why globular clusters?

E, Sa galaxies:

v 150km (R 850)

Milky Way GCs:

v 2-18 (R 7-60 k)

-7 > Mv > -9 10,000 < R < 30,000

Element-yield review:

< 2M: H C2-8M: H C/O/Ne, n-capture (s-

process)[binary] SN Type I: Fe-peak

8-30M: HFe, SN Type II: Fe-peak, -

elements, n-capture (r-process)

Punch line:

“-elements” ………………… SN II:fast (Myrs)

(O,Mg, Si,S,Ca, Ti; Al,Na?)

Fe:………………………………… SN I: slow (Gyrs) SN II:fast

Fe-peak (21-30p) :………… SN I: slow (Sc, V, Cr, Mn, SN II:fast Co, Ni, Cu, Zn) Fe-dep. yields?

Heavy(Ba, Y, Zr, La, Sr…) ………… SN I: slow(Eu, Sm, Nd…) ………………… SN

II:fast

Why get detailed abundances?

Prochaska et al 2000, Bensby et al 2004


Element-yield review:

(X) = relative number = (x/H) = log (N(X)/N(H))

+ 12

[Fe/H] = log(Fe/H) - log(Fe/H)

[X/Fe] = (X/Fe) - (X/Fe)

z = mass fraction beyond He z= 0.019



Prochaska et al 2000

deficient

enriched

Metalpoor

[/Fe] vs [Fe/H] : formation timescale

[Eu/Fe] : r-process (SNII) IMF, nucleosynthesis

[Ba/Fe] : s-process (SNI, low-m), IMF, nucleosynthesis


*1- Detailed formation of galaxy #2

2- test stellar population models

3- understand the line indices


Prochaska et al 2000

deficient

enriched

Metalpoor



The goal: GC abundances outside the local group…

Requirements:

S/N 50 HR 10,000 – 30,0003500-9500 A

MIKE + Magellan:

GC limit 18 V mag

Bernstein, Shectman, Gunnels, installed Nov 2002

NGC 5128: S0(Dec = -43)

D = 3.5 Mpc m-M = 27.7

GCs: Mv 17-20 mag

(RGB tip: v 25-26 mag)(young supergiants)

Rejkuba 2001 (UVES/FORS imaging)

The goal: Galaxies outside the local group…

The goal: Galaxies outside the local group…



NGC 1313: SBd(Dec = -66)

D = 4.4 Mpc m-M = 28

GC: v 17-20 mag

(RGB tip: v 25-26 mag)

High resolution analysis — A Training Set

The Milky Way Globular Clusters (= 14-16 mag/asec2):


[Fe/H] = -2.0 v = 4km/s

V = -6 mag

vs

[Fe/H]=-0.76 v = 12km/s V = -9 mag

Milky Way GCs: GC Integrated Light Spectra (ILS) at different abundances & masses


NGC 104 (47Tuc):

[Fe/H] = -0.76 v = 12 km/s

V = -9 mag

Eu in RGB: EW= 16 mÅ!

Milky Way GCs: ILS spectrum vs single RGB

A Training Set:

Milky Way: 7 clusters (= 14-16 mag/asec2):[Fe/H] Mv

ngc 6397 -1.95 -6.6ngc 6093 -1.75 -8.23ngc 6752 -1.42 -7.7ngc 2808 -1.36 -9.35ngc 362 -1.16 -8.4

ngc 104 (47Tuc) -0.76 -9.4ngc 6388 -0.60 -9.8

LMC: 7 clusters to date (m-M=18.5, mv=10 mag, v= 14-16 mag/asec2)

ngc 2019, 2005 [Fe/H] ≈ -2.0 old (>5 Gyr) ngc 1866, 1978 [Fe/H] ≈ ? intermediate (0.1-1.5

Gyr)ngc 1711, 2002, 2100 [Fe/H] ≈ -0.6 young (<0.1 Gyr)



Training Set: observations

Milky Way (6) + LMC (8) :

Integrated light spectra

32”x32”

12”x12”

1”x4” slit

1”x4” slit

MW: 47Tuc

LMC: n1711

individual stars



Training Set: analysis?

Individual stars: EWobs vs. Modeled stellar atmospheres

- Kurucz stellar atmosphere grids (ATLAS9)

Teff *(B-V)obs log g *(V) obs *(1-2 km/s)[Fe/H]

mass,T,P,N(e-)

- MOOG (Sneden 1998), for each line:

, EP, loggf, (X)

EWmod

*tune to get same (Fe) for all FeI,II lines.

Training Set: analysis

Integrated light: EWobs vs ???

Build up an atmosphere model.

RESOLVED globular cluster --> observed CMD!

Training Set: analysis

Integrated light: EWobs vs composite model atmosphere

- Kurucz stellar atmosphere grids (ATLAS9)

Teff (B-V)obs

log g (V) obs

log g [Fe/H]

- MOOG (Sneden v.1998), for each line:

, EP, loggf, (X)

EW per box.

Combine to get light-weight EW

* NO PARAMETER TUNING

Training Set: step 0 - observed CMD

RESOLVED globular cluster --> observed CMD!

Training set issues: scanned core only!

rare stars not included.

Training Set: step 0 - observed CMD (n6397)

NGC 6397: Stable FeI solution: Is (Fe) stable with lines’ Excitation Potential

Checks Teff, reddening:

Population of energy state depends on T


NGC 6397: Stable FeI solution: Is (Fe) stable with lines’ wavelength

Checks fraction of flux from hot/cool stars:

blue light -- from hot stars with weak lines

red light -- cool stars with strong lines.


NGC 6397: Stable FeI solution: Is (Fe) stable with lines’ EW.

Checks ( log g, 1-2 km/s)

Microturbulence decreases saturation of strong lines.

(0km/s larger covering factor in wavelength space. Larger velocities “spread” the atoms in wavelength space, decreasing saturation.)


Balmer lines: equivalent widths (EW) and profiles example: NGC 6397 - member RGB star

NGC 6397 - ILS 47 Tuc - ILS

Broadened by hot stars

Age/Metallicity: Old/metal-rich = red (cool) Young/metal-poor = blue (hot)


Balmer lines: H, H, H, H — EW and profiles

— ILS NGC 6397— synthesized lines from the observed CMD (w/ BHB) (w/o BHB)

Age/Metallicity +HB morphology

Observational constraint: flux in / color of HB

(otherwise, HB is a wild card…Age? mass loss?)


ILS analysis[Fe/H]

x (x) N-lines /N [X/Fe] [X/Fe] Cr 2.93 3 0.26 0.18 -0.53FeI 5.30 63 0.26 0.03 -2.2 -1.97FeII 5.35 8 0.35 0.12 -2.15 -2.20NiI 4.18 2 0.09 0.09 0.13

-elements:MgI 5.47 4 0.45 0.23 0.10CaI 4.43 8 0.15 0.06 0.28 0.64TiI,II 3.20 13 0.38 0.11 0.37 0.36

n-capture BaII 0.02 7 0.22 0.08 0.02 0.10

(Castihlo 2000)

NGC 6397: Derived abundances — consistent with results from single stars!

What (we think) we know from analysis of a RESOLVED GC (n6397):

1. the composite stellar models can work!

2. We have tools to identify problems!

Balmer lines Teff (CMD: reddening, {age, [Fe/H]}, HB morph)

FeI (EW, EP, )

FeI vs Fe II log g (CMD: giants vs dwarfs, age)(ionized lines sensitive to N(e-))

RECAP —

Training Set: step 1 - isochrone CMD (47Tuc)

GCs are a single age population!

Isochrones - stellar evolution models predict cluster CMD at given age.

Padova (Girardi et al 2000) BaSTI (Pietrinferni et al 2004)

+ Kroupa IMF (Kroupa & Boily 2002), flattens below 0.5M

+ Normalize #’s of stars to observed Mv

(In the case of a faint cluster, don’t make boxes w/ <1 star)

What if the cluster is unresolved? (e.g. NGC 1313 -379)


Do they reproduce the CMD?

2 problems:

1. mass segregation (for training set)

2. AGB bump (general)

47Tuc

Schiavon et al 2002

Spitzer & Hart 1971MW: eg. Ferraro 1997LMC: eg.Grijs et al 2002


Do they reproduce the CMD?

Adjustments:1- remove stars 3 mag below turn-off.2- increase fraction in AGB bump.

Training Set: step 1 - isochrone CMD (4 GCs)

1- Balmer lines -

H, H, H, H EW and profile

Models: age = 6.3 Gyr z = 0.0001-0.01

* note blends


1- Balmer lines -

H, H, H, H EW’s

Color = AGE

NGC 6397 match:

Age ≈ 6.3 Gyr[A/H] ≈ -2

Models changevery little > 3 Gyrs


1- Balmer lines -

H, H, H, H EW’s and profiles

Models: age = 10 Gyr z = 0.0001-0.01

*note blends are worse!! (metal rich GC) Need to synthesize blended lines


1- Balmer lines -

H, H, H, H EW’s

47Tuc match:

Age ≈ 10-12 Gyr[A/H] ≈ -0.9

2- FeI & FeII

Training Set: step 2 - isochrone CMD (47 Tuc)

(Padova, unadjusted isochrones)

2- FeI & FeII

[FeI/H] input [A/H] input age



2- FeI & FeII


+/-0.1 !!

at <1 Gyr: young = hot modeled lines=weak. at >1 Gyr: models not changing much




FeI checks: no FeI slope w/ EP if: age > 2 & [A/H] < -1

w/ if: age > 3 w/ EW if: age > 3 Gyrs

2- FeI & FeII


+/- 0.05 !!

[FeII/H] input [A/H] input age




The age-metallicity degeneracy!

2- FeI & FeII


+/- 0.05 !!

[FeII/H] input [A/H] input age

expected age to increase giant:dwarf… g … N(e-).



2- FeI & FeII


+/-0.05 !! (statistical)

[FeII/H] input [A/H] ( N(e-)) input age

[Fe/H]=[FeII/H]:[Fe/H] -0.6age = 5-16 Gyrs

Best FeI solution: [Fe/H] -0.6(10Gyr, [A/H]=-0.68)




1- iron peak

x (x) N-lines [X/Fe][Fe/H] [X/Fe] (C’04) Sc II 2.53 ... 1 +0.13 +0.13V I 3.40 0.31 5 +0.11 +0.05Cr I 4.87 0.14 3 -0.19 +0.11Mn I 4.49 0.30 4 -0.31 -0.29Fe I 6.78 0.24 71 -0.73 -0.67, -0.79 (KI’03)Fe II 6.81 0.15 8 -0.70 -0.56Ni I 5.47 0.18 12* -0.05 +0.06

Abundance results for 47Tuc!

Carretta et al 2004Kraft & Ivans 2003(Padova, 10Gyr, [A/H]=-0.68, adjusted)

Isochrone analysis (w/ mass segregation +boosted AGB dump)

CONSISTENT with solution from individual stars.

unambiguous [Fe/H]=0.7


(Padova, 10Gyr, [A/H]=-0.68, adjusted)



2. -elements

x (x) N-lines [X/Fe] [X/Fe] (CG04)[O I] 8.45 ... 1 +0.45 +0.23 Mg I 7.02 ... 1 +0.17 +0.40Si I 7.16 0.21 6 +0.33 +0.30Ca I 5.81 0.24 12 +0.19 +0.20Ti I 4.55 0.24 13 +0.34 +0.26Ti II 4.68 0.16 3 +0.44 +0.38

3- non-alpha, light elements

Na I 5.97 0.19 3 +0.38 +0.23 Al I 6.19 0.02 2 +0.43


Carretta & Gratton 2004



4- neutron-capture elements (s-, r-process)

x (x) N-lines [X/Fe] [X/Fe]Y II 1.34 ... 1 -0.19 +0.49? (Brown+Wallerstein’89)

Y I: 1.29 ... 1 -0.24 Zr I 1.80 0.21 2* -0.08 -0.22?Ba II 1.41 0.09 3* -0.11 La II 0.57 0.38 2 +0.05Nd II 0.80 ... 1 +0.01Eu II -0.12 ... 1 +0.04 +0.36?



Results for 47Tuc:

-elements:

Similar to halo/bulge.

Exactly as expected.

light-elements: (Na, Al)

HIGH!

Consistent with proton-burning(self-enrichment!) in GCs: NeNa, MgAl

Gratton, Sneden, Carretta 2004


Results on 47Tuc:halo thick bulge thin

Fe-Peak elements:

Similar to halo/bulge.

Exactly as expected.

Results on 47Tuc:

Heavy elements: (r-, s-process)

Similar to halo… close to solar.

Sites of r-process not well known.Differences in SN yields with metallicity…

Second Training Set - LMC

Important because:

1- MW GCs all age > 8 Gyrs … LMC 0.1 < Age < 5 Gyr

2- Test the standard model for chemical enrichment!

[/Fe] > 0 when metal poor, [/Fe] ~ 0 when metal rich

Single stars: Magellan+MIKE (VLT+UVES)

ILS: 2.5m telescope

EXTRAGALACTIC GCs -- first round targets

NGC 5128: S0, D = 3.5 Mpc m-M = 27.7 Mv 17-20 mag

hghh23 Mv=18.3 B-V=1.1 (red) Peng et al. 2003 hghh29 Mv=18.2 B-V=1.0 (red) hghh17 Mv=17.6 B-V=0.8 (blue)

NGC 1313: SBd, D = 4.4 Mpc, m-M = 28.2 Mv 17.5-20.5 mag

379: Mv=17.6 B-V=0.27 (blue) Larson et al 1999

EXTRAGALACTIC GCs — first peak…

Next steps:

1. MW & LMC - new abundances results- mass estimates- finish the “training”

2. NGC 5128 & NGC 1313- first metallicities in *old* extragalactic environment

a method for obtaining detailed abundances of extragalactic globular clusters

Documents

burstein et

abundances fe

ivans et

fastprochaska et

perrett et

trager et

yanny et

gonzalez et