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INSTITUTO DE ASTROFÍSICA DE CANARIAS Alexandre Vazdekis Stellar spectral libraries for stellar population models
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
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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…
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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, …
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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
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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
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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
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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
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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…
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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
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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
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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
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Thomas+11
α-enhancement effects on indices not dominated by Mg or Fe:
more in THOMAS talk
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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:
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Coelho+07
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Conroy & van Dokkum 12
These models
allow a deeper
understanding of
what each index
is made from
Element ratios of
the SDSS ETGs
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Not always all these line-strength predictions agree among the
various models:
More in SCHIAVON and THOMAS talks
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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
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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
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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
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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
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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
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• 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
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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)
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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
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• Very sensitive to the youngest
stellar contributions
• UV upturn
• Promising absorption indices
Kaviraj+07
SHARDS
Yi+11
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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
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Cenarro+03
Spiniello+14
La Barbera+13
A. Vazdekis Instituto de Astrofísica de Canarias
New empirical
stellar libraries
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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
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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
