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INSTITUTO DE ASTROFÍSICA DE CANARIAS
Alexandre Vazdekis
Stellar spectral libraries for
stellar population models
A. Vazdekis Instituto de Astrofísica de Canarias
Stellar population synthesis
models & main ingredients
2
Fl (m,T(to),g,Z)IMF (m)dm = SSP
ISOCHRONES:BaSTI,Dartmouth,
Geneva, Lyon, Padova, Victoria-
Regina, Weiss+, Y^2, …
STELLAR LIBRARIES: Coelho+,
ELODIE, Kurucz, Lick, MILES,
Pickles, PHOENIX, STELIB…
Sánchez-Blázquez+06
Bertelli+94
Bruzual&Charlot+03
Bruzual&Charlot, Coelho+, FSPS,
GALEV, Kodama&Arimoto, Maraston
&Thomas, MILES, Padova, PEGASE,
Schiavon,Starburst, Worthey,YEPS…
A. Vazdekis Instituto de Astrofísica de Canarias 3
Model predictions
Photometric properties (colours, M/L, SBFs): (Arimoto & Yoshii
86, Bruzual & Charlot 93, Buzzoni 94, Bressan+94, Worthey 94,
V+96, Kodama & Arimoto 97, Leitherer +98, Maraston 98,05…)
Lick line-strength indices: Peletier 89, Worthey 94, V+96,
Tantalo+98, Thomas+03, Schiavon 07, Chung+13,…
Very low resolution spectra: Bruzual & Charlot 93, Bressan+94,
Kodama & Arimoto 97, Leitherer+98, Maraston 05, Conroy+09…
High resolution spectra: V99, Schiavon+02, V03, Bruzual &
Charlot 03, Le Borgne+04, Gonzalez-Delgado+05, V+10,
Maraston & Strömbäck 11, Conroy & van Dokkum 12, …
A. Vazdekis Instituto de Astrofísica de Canarias 4
Line-strength predictions
Li & Han 07
Optical colours cannot break the age-metallicity degeneracy:
If combined with
near-IR colours it
is possible if the
stellar populations
are not too old
A. Vazdekis Instituto de Astrofísica de Canarias 5
The Lick/IDS stellar library and the Lick index system:
~450 stars:
o Low spectral resolution: varying with l (FWHM ~ 8.5–11 Å)
o Wide coverage stellar atmospheric parameters (Teff,logg,[Fe/H])
o Non flux-calibrated stellar spectra (Lick/IDS response curve)
Burstein+84, Faber+85,Gorgas+93,Worthey 94, Worthey & Ottaviani 97
25 indices from CN at ~4150Å to TiO2 at ~6200Å
A. Vazdekis Instituto de Astrofísica de Canarias 6
Empirical Fitting Functions: index = FF(Teff,logg,[Fe/H])
(Worthey+94; Worthey & Ottaviani 97)
Other FFs: Thevenin+97, Cenarro+02, Schiavon+07, Mármol-Queraltó+07, Thomas+10…
Requirements for applying these model predictions:
o Smooth observed galaxy spectra to match Lick/IDS resolutions
o Transform data to the response curve of the Lick/IDS spectrograph
o Correct for galaxy velocity dispersion
Too rigid to be able to exploit high quality observations at varying z
Most stellar population studies were achieved with this approach
A. Vazdekis Instituto de Astrofísica de Canarias 7
High resolution stellar spectral libraries
Theoretical libraries:
o Updated line/molecular lists. NLTE required for some lines…
o Libraries: Barbuy+03, Murphy & Meikisin 04, Zwitter+04, Coelho+05,
Martins+05, Munari +05, Rodriguez-Merino+05, Frémaux+06,
Leitherer+10, Palacios+10, Sordo+10, Kirby 11, de Laverny+12,
Coelho+14…
To be tested
with real stars:
Coelho 14
A. Vazdekis Instituto de Astrofísica de Canarias 8
Empirical stellar spectral libraries:
Excellent atmospheric parameter coverage (Teff,logg,[Fe/H])
Flux-calibrated spectral response
Cover the various stellar evolutionary phases
Some popular libraries: Jones 99, CaT (Cenarro+01), ELODIE (Prugniel
& Soubiran 01), STELIB (Le Borgne+03), INDO-US (Valdes+04), IRTF
(Cushing+05), MILES (Sánchez-Blázquez+06), NGSL (Gregg+06)
• See an extensive list in David Montes webpage:
pendientedemigracion/ucm.es/info/Astrof/invest/actividad/spectra.html
• Some models: V 99, V12, Bruzual & Charlot 03, Le Borgne+04, Maraston
& Strömbäck 11, Conroy & van Dokkum 12…
A. Vazdekis Instituto de Astrofísica de Canarias 9
The larger the stellar parameter coverage the better:
V+10
Sánchez-Blázquez+06
It is also key to achieve an
accurate flux-calibration
A. Vazdekis Instituto de Astrofísica de Canarias
10
Fitting on galaxy
spectrum´s system!
V & Arimoto 99
V+10
A. Vazdekis Instituto de Astrofísica de Canarias
Easy to define newly optimised
indices sensitive to relevant
stellar population parameters:
11
Thomas+03
Cervantes & V 09
Hβ
Hβo
Age
A. Vazdekis Instituto de Astrofísica de Canarias
Abundance
ratios
Base models: Scaled-solar isochrones
+
Empirical spectra
(s-s @ solar metallicity;
α-enhanced @ low metallicity)
Milone+12
Scaled-solar models: Scaled-solar Isochrones
+
Scaled-solar spectra
α-enhanced models: α-enhanced or s-s isochrones
+
α-enhanced spectra
Dotter+08
Davies+93
A. Vazdekis Instituto de Astrofísica de Canarias 13
Thomas+03
More massive
galaxies show
larger [Mg/Fe]
(shorter formation
timescales)
Index response functions to abundance element variations from theoretical atmospheres (Tripicco & Bell 95, Korn+05…) to correct the base models (Tantalo & Chiosi 98,04, Trager+00, Thomas+03, Korn+04, Li&Worthey 05, Schiavon 07, Graves+08, Thomas+11)
Schiavon 07
α-enhanced and
scaled-solar grids
A. Vazdekis Instituto de Astrofísica de Canarias 14
Thomas+11
α-enhancement effects on indices not dominated by Mg or Fe:
more in THOMAS talk
A. Vazdekis Instituto de Astrofísica de Canarias 15
Increasing effects with increasing age/metallicity
V+14
High resolution α-enhanced stellar populations model SEDs: • Fully theoretical: employing α-enhanced theoretical stellar
spectral library (Leitherer+99, Delgado+05, Coelho+07, Buzzoni+09, Lee+09, Percival+09, Maraston & Strömbäck 11)
• Semi-empirical: apply a differential correction computed from stellar atmospheres to correct the reference models based on an empirical library (Cervantes+07, Prugniel+07, Walcher+09, Conroy & van Dokkum 12, V+14)
A. Vazdekis Instituto de Astrofísica de Canarias
α-enhanced isochrones vs. α-enhanced stellar library:
The effects from the latter are more relevant for most metallicity
indicators except for the Balmer lines:
16
Coelho+07
A. Vazdekis Instituto de Astrofísica de Canarias 17
Conroy & van Dokkum 12
These models
allow a deeper
understanding of
what each index
is made from
Element ratios of
the SDSS ETGs
A. Vazdekis Instituto de Astrofísica de Canarias 18
Not always all these line-strength predictions agree among the
various models:
More in SCHIAVON and THOMAS talks
A. Vazdekis Instituto de Astrofísica de Canarias 19
A more empirical approach relying solely on base model grids: • Plot an age indicator vs. Mg-sensitive and vs. Fe-sensitive indices.
• Obtained metallicity difference [ZMg/ZFe] good proxy for the abundance ratio
(V+01, Yamada+06, Sánchez-Blázquez+07, La Barbera+13…)
Yamada+06
La Barbera+13
…it also picks the sensitivity of other indices to [ZMg/ZFe]
SDSS ETGs
A. Vazdekis Instituto de Astrofísica de Canarias 20
Carretero+04
• Shorter formation
timescales in more
massive clusters
Mg C,N Fe
time
CN abundance ratio in
galaxies with
σ~200km/s is linked to
galaxy cluster mass:
• Timescales are
shorter than 1Gyr in
all galaxy clusters
A. Vazdekis Instituto de Astrofísica de Canarias 21
Extended SFH: separating the various stellar components
Breaking burst-age burst-strength degeneracy via specifically
designed line-strength diagnostic diagrams:
Kauffmann+03
Leonardi & Rose 96
Young
Old
A. Vazdekis Instituto de Astrofísica de Canarias 22
Use different spectral ranges:
Comparison of ages derived in two spectral ranges for 98 galaxies:
• Coma: compatible with SSPs
• Field: multiple bursts
Sánchez-Blázquez+07
8.9Gyr
9.3Gyr
8.5Gyr
11.0Gyr
COMA FIELD
A. Vazdekis Instituto de Astrofísica de Canarias 23
Full spectrum-fitting: STARLIGHT(Cid-Fernandes 05,
VESPA (Tojeiro+09),
STECKMAP(Ocvirk+06),
ULySS (Koleva+09)
…
Tojeiro+09
Quiescent Star Forming
Cluster@z=0.83
Ferré-Mateu+14
A. Vazdekis Instituto de Astrofísica de Canarias 24
• Unlike indices full spectrum-fitting is sensitive to the
continuum for the ¨good ¨(colours, wide molecular bands…)
and for the ¨bad¨ (e.g. dust, flux-calibration issues…)
da Cunha+08
More in
CHARLOT
talk
A. Vazdekis Instituto de Astrofísica de Canarias 25
Mayya 97
Using line-strength indices in the near-IR range:
There are
indicators, such
as, CaII triplet or
the CO
bandhead that
are very
sensitive to the
supergiants
phase, which is
characteristic
feature of rather
young ages
(~10Myr)
See MARASTON
talk for AGB-
dominated age
regimes (~1Gyr)
A. Vazdekis Instituto de Astrofísica de Canarias 26
Röck+14
Beyond the K band:
IRTF library
(Cushing+05; Raynier+09)
~200 stars, accurate flux-calibration
0.8-5µ (reaching Spitzer [3.6],[4.5])
R=2000, σ=60km/s
Extended MILES models (Röck+14)
A. Vazdekis Instituto de Astrofísica de Canarias
The UV spectral range
27
• Very sensitive to the youngest
stellar contributions
• UV upturn
• Promising absorption indices
Kaviraj+07
SHARDS
Yi+11
A. Vazdekis Instituto de Astrofísica de Canarias 28
NGSL: HST-based library (378 stars observed with 3 gratings) (Gregg+06)
V+14
Koleva & V 13
Models at higher resolution in the UV (FWHM=3Ǻ)
A. Vazdekis Instituto de Astrofísica de Canarias
The IMF
IMF sensitive atomic
and molecular lines.
And also redder
colours.
Ca Na
Na
TiO TiO
V+12
29
Cenarro+03
Spiniello+14
La Barbera+13
A. Vazdekis Instituto de Astrofísica de Canarias
New empirical
stellar libraries
30
The XSL library: -X-shooter@VLT
~600 stars
- R>8000
- 0.3 – 2.5µ
M stars LPV, C, S & L stars
Chen+14
Warm stars
Extended MILES: - IDS@INT
- [Mg/Fe] coverage
~ 250 newly obs. stars
MANGA library:
-SDSS range/resolution
-Homogeneous params
~8000 stars
A. Vazdekis Instituto de Astrofísica de Canarias 31
About the IMF…
? Supersolar metallicity regime
? Very low mass stars. Do matter?
? Model predictions disagree
? Is M/Lstars > M/Ldyn
? Is the IMF a local property
CONROY, LA BARBERA,
SMITTH, SPINIELLO, YI talks
Spiniello+14
Conroy 13
La Barbera+13 Martin-Navarro+14
Conroy 13
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