A Method for Obtaining Detailed Abundances of Extragalactic Globular Clusters
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Transcript of 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
Formation history of other galaxies:
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
Formation history of other galaxies:
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
halo thick bulge thin
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
halo thick bulge thin
Why get detailed abundances?
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
Why get detailed abundances?
*1- Detailed formation of galaxy #2
2- test stellar population models
3- understand the line indices
halo thick bulge thin
Prochaska et al 2000
deficient
enriched
Metalpoor
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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…
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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):
High resolution analysis — A Training Set
[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
High resolution analysis — A Training Set
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)
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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
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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
Training Set: step 0 - observed CMD (n6397)
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.
Training Set: step 0 - observed CMD (n6397)
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.)
Training Set: step 0 - observed CMD (n6397)
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)
Training Set: step 0 - observed CMD (n6397)
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?)
Training Set: step 0 - observed CMD (n6397)
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)
Training Set: step 1 - isochrone CMD (47Tuc)
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
Training Set: step 1 - isochrone CMD (47Tuc)
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
Training Set: step 1 - isochrone CMD (4 GCs)
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
Training Set: step 1 - isochrone CMD (4 GCs)
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
Training Set: step 1 - isochrone CMD (4 GCs)
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
Training Set: step 2 - isochrone CMD (47 Tuc)
(Padova, unadjusted isochrones)
2- FeI & FeII
[FeI/H] input [A/H] input age
+/-0.1 !!
at <1 Gyr: young = hot modeled lines=weak. at >1 Gyr: models not changing much
Training Set: step 2 - isochrone CMD (47 Tuc)
(Padova, unadjusted isochrones)
Training Set: step 2 - isochrone CMD (47 Tuc)
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
[FeI/H] input [A/H] input age
+/- 0.05 !!
[FeII/H] input [A/H] input age
Training Set: step 2 - isochrone CMD (47 Tuc)
(Padova, unadjusted isochrones)
Training Set: step 2 - isochrone CMD (47 Tuc)
The age-metallicity degeneracy!
2- FeI & FeII
[FeI/H] input [A/H] input age
+/- 0.05 !!
[FeII/H] input [A/H] input age
expected age to increase giant:dwarf… g … N(e-).
Training Set: step 2 - isochrone CMD (47 Tuc)
(Padova, unadjusted isochrones)
2- FeI & FeII
[FeI/H] input [A/H] input age
+/-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)
Training Set: step 2 - isochrone CMD (47 Tuc)
(Padova, unadjusted isochrones)
Training Set: step 2 - isochrone CMD (47 Tuc)
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
Training Set: step 2 - isochrone CMD (47 Tuc)
(Padova, 10Gyr, [A/H]=-0.68, adjusted)
Abundance results for 47Tuc!
Training Set: step 2 - isochrone CMD (47 Tuc)
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
(Padova, 10Gyr, [A/H]=-0.68, adjusted)
Carretta & Gratton 2004
Abundance results for 47Tuc!
Training Set: step 2 - isochrone CMD (47 Tuc)
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?
(Padova, 10Gyr, [A/H]=-0.68, adjusted)
Abundance results for 47Tuc!
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
halo thick bulge thin
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…
EXTRAGALACTIC GCs — first peak…
EXTRAGALACTIC GCs — first peak…
EXTRAGALACTIC GCs — first peak…
EXTRAGALACTIC GCs — first peak…
EXTRAGALACTIC GCs — first peak…
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