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The Magellanic Clouds
Chemical Enrichment
History and Its Gradients Via
CaII-Triplet Spectroscopy
Ricardo Carrera (I.A.C.)
Carme Gallart (I.A.C.)
Antonio Aparicio (I.A.C.)
Edgardo Costa (Universidad de Chile)
Eduardo Hardy (N.R.A.O.)
René Méndez (Universidad de Chile)
Noelia Noël (I.A.C.)
Elena Pancino (INAF-OAB)
Robert Zinn (Yale University)
How do galaxies evolve?
Star Formation History Ingredients:
•Initial Mass Function.
•Binary Fraction.
•Star Formation Rate (t).
Color-Magnitude Diagram
•Chemical Enrichment Law.
Color-Magnitude Diagram
Spectroscopy
The Ca II Triplet as Metallicity
Indicator
Why a new Calibration?
Extend it to more metal-rich regimes.
Investigate the influence of younger ages.
Cluster Sample
15 Galactic Globular and 14 Open Clusters
-2.2[Fe/H]+0.47 and 0.25(age/Gyr)
Ca=W8498+W8542+W8662
The Magellanic
Clouds
LMC Age-Metallicity Relationship
Planetary
Nebulae
Clusters
Dirsch et al. 2000
Dopita et al. 1997
Cole et al. 2005
Bar field
populations
Observed Fields
van der Marel 2001
Staveley-Smith et al. 2003
Observed Fields
Z=0.002: 13.5, 10 & 8 Gyr
Z=0.004: 5 & 4 Gyr
Z=0.008: 2.5, 1.5, 0.2 & 0.03 Gyr
Observations
December 2002
January 2005
HYDRA@CTIO 4m
[Fe/H]≤-1.5
-1.5≤[Fe/H]≤-1.
-1≤[Fe/H]≤-0.5
X -0.5≤[Fe/H]≤0
0<[Fe/H]
No correlation
between [Fe/H] and
position of the star in
the CMD
Metallicity Distribution
Metallicity Gradient
Field
Bar
o
3
o
5
6o
8o
[Fe/H]
-0.39
-0.47
-0.50
-0.45
-0.79
[Fe/H]
0.19
0.31
0.37
0.31
0.44
[Fe/H ]-1
8%
12%
23%
18%
34%
-1<[Fe/H]
92%
88%
77%
82%
66%
0
[Fe/H]
[Fe/H]
0
-1
-2
-1
-2
2
10
Age (Gyr)
2
10
Age (Gyr)
Age Determination
RGB age-metallicity degeneracy.
Age: more metal-rich stars are redder.
Metallicity: older stars are also redder.
[Fe/H] Spectroscopy
Age
Position of stars on the CMD
Pont et al. 2004
Cole et al. 2005
Age determination uncertainty larger than metallicity one.
Only interested in global tendency.
Age-Metallicity Relationships
Disk Chemical Evolution Models
Parameters
Yield=0.014
R=0.44
Zi=0
µf=Mg/Mb=0.21
(t)
 & 
Models
Closed-box
Infall
Outflow
Infall+outflow
The Small Magellanic Cloud
SMC Age-Metallicity Relationship
Clusters
Small
Magellanic
Cloud
13 Fields
3 Eaest
4 West
6 South
Stanimirovic et al. 2006
Observed Fields
1º4
1º6
1º7
1º3
East
1º4
Noël et al. 2007
See Noelia Noël talk
1º4
2º3
2º7
2º9
3º0
4º0
South
2º0
West
Observations
Service Mode
FORS2 MXU@VLT
Metallicity Distributions
East
West
South
Metallicity Distributions
Field
r(o)
[Fe/H]
[Fe/H
-1[Fe/H]
[Fe/H]<-1
]
smc0057
1.1
-1.01
0.33
47
53
qj0037
1.3
-0.95
0.17
65
35
qj0036
1.3
-0.98
0.25
51
49
qj0111
1.3
-1.08
0.21
36
64
qj0112
1.4
-1.16
0.32
31
69
qj0035
1.6
-1.09
0.24
34
66
qj0116
1.7
-0.96
0.26
57
43
smc0100
2.2
-1.07
0.28
39
61
qj0047
2.7
-1.20
0.17
29
71
qj0033
2.9
-1.58
0.57
15
85
smc0049
2.9
-1.00
0.28
47
53
qj0102
3.0
-1.29
0.42
26
74
smc0053
3.9
-1.64
0.50
8
92
Why this gradient?
0
[Fe/H]
[Fe/H]
0
-1
-2
-1
-2
2
10
Age (Gyr)
2
10
Age (Gyr)
Age-Metallicity Relationships
East
West
South
The SMC Chemical Evolution Models
Parameters
Yield=0.014
R=0.44
Zi=0
µf=Mg/Mb=0.25
(t)
 & 
Models
Closed-box
Infall
Outflow
Infall+outflow
East
West
South
Conclusions
The CaT is metallicity indicator for 0.25(Age/Gyr)13
& -2.2[Fe/H]+0.47. Linear correlation with [Fe/H] in
CG97 & KI03. Age influence negligible within the
uncertainties.
The LMC disk metallicity is constant except for the
outermost field which is a factor 2 more metal-poor. This
is explained by the lack of young, and also metal-rich,
stars in this field. The chemical evolution has been the
same in all the fields in our sample.
The SMC has a lower average metallicity than the LMC.
This galaxy has a metallicity gradient in the sense that
metal-rich
stars,
which
are
also
younger,
are
concentrated in the central regions of the galaxy.