INSTITUTO DE ASTROFÍSICA DE CANARIAS - Oxford Physics · Instituto de Astrofísica de Canarias 8...

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, …


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


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


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


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


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…


The larger the stellar parameter coverage the better:

V+10


It is also key to achieve an

accurate flux-calibration


10

Fitting on galaxy

spectrum´s system!

V & Arimoto 99

V+10


Easy to define newly optimised

indices sensitive to relevant

stellar population parameters:

11

Thomas+03

Cervantes & V 09

Hβ

Hβo

Age


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


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


Thomas+11

α-enhancement effects on indices not dominated by Mg or Fe:

more in THOMAS talk


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)


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


Conroy & van Dokkum 12

These models

allow a deeper

understanding of

what each index

is made from

Element ratios of

the SDSS ETGs


Not always all these line-strength predictions agree among the

various models:

More in SCHIAVON and THOMAS talks


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


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


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


Use different spectral ranges:

Comparison of ages derived in two spectral ranges for 98 galaxies:

• Coma: compatible with SSPs

• Field: multiple bursts


8.9Gyr

9.3Gyr

8.5Gyr

11.0Gyr

COMA FIELD


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


• 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


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)


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)


The UV spectral range

27

• Very sensitive to the youngest

stellar contributions

• UV upturn

• Promising absorption indices

Kaviraj+07

SHARDS

Yi+11


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)


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


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


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

INSTITUTO DE ASTROFÍSICA DE CANARIAS - Oxford Physics · Instituto de Astrofísica de Canarias 8...

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