Download Progress Report G. Bruzual and S. Charlot

Uncertainties in Population Synthesis
Models: Applications to Local and
Distant Galaxies
Gustavo Bruzual A.
CIDA, Mérida, Venezuela
Motivation:
Look at some problems or failures of current generation of
population synthesis models and see what is the best we
can do to understand them using available tools and
data.
What we would like to have in the years to come…
My view:
There is not a perfect model or set of models. Depending on the
application, a set of models built with a particular set of ingredients
may be optimal.
Most data sets are incomplete and may remain incomplete for a long
time
Work in collaboration with S. Charlot (soon to be published, CB10).
Typical
Isochrone
Marigo et al. (2008)
Theoretical HRD
Typical
Isochrone (detail)
Marigo et al. (2008)
Theoretical HRD
Stellar
libraries:
wavelength
coverage
Stellar
libraries:
Teff
coverage
IndoUS, Miles,
and Stelib
[Fe/H]
Distribution
Complete near
Solar (more or less)
Increasing spectral resolution
• Coelho (< 1Å)
• IndoUS (~ 1Å)
• Miles (2.4 Å)
• Stelib (3 Å)
• HNGSL (~ 5Å)
• Pickles (5 Å)
• Kurucz (20 Å)
Padova 94 tracks
Behaviour of line strength indices:
Models vs SDSS bright galaxies
IndoUS (new)
Stelib (BC03)
Caution:
Flux calibration
problem in
IndoUS library.
Calibration
and stellar
parameters
under revision
by Prugniel
and
collaborators
STIS NGSL UV coverage
NGSL (black) vs IUE
(cyan) and Kurucz
models (green)
Solar metallicity
1 Gyr SSP
Chabrier IMF
Padova 1994 tracks
STIS NGSL is being
enlarged and recalibrated
by Lindler & Heap and
collaborators
STIS NGSL UV coverage
NGSL vs Kurucz models
(green)
Z = 0.2 x Solar (blue)
0.4 x Solar (cyan)
1.0 x Solar (red)
12 Gyr SSP
Chabrier IMF
Padova 1994 tracks
Problem 1:
Incompleteness of stellar libraries
U-UV spectral range.
Excess of U flux in population models built using incomplete
stellar libraries.
Completeness matters
Walcher et al. (2008): VVDS data (grey shading) vs. models (contours)
Conclude that the wavelength range from
3300 to 4050 Å is not correctly reproduced by
models based mostly in the Miles library, which
contains few hot stars.
Walcher et al. (2008):
Excess U flux is clearly seen in fit to typical
galaxy sed
Improving the U-UV spectral range
Tlusty Models:
Grid of NLTE plane parallel hydrostatic model atmospheres for:
O-stars: Lanz & Hubeny (2003)
B-stars: Lanz & Hubeny (2007)
High spectral resolution from 54.8 Å to FIR (R = 50,000)
15,000 ≤ Teff ≤ 55,000 K;
0 ≤ Z ≤ 2 x Zo
Improving the U-UV spectral range
Martins et al. (2005) Models:
Grid of NLTE plane parallel hydrostatic model atmospheres
Coverage:
3,000 ≤ Teff ≤ 27,500 K;
0.10 x Zo ≤ Z ≤ 2 x Zo
3000 to 7000 Å (R = 20,000)
Improving the U-UV spectral range
UVBLUE and BLURED:
Grid of model atmospheres based on Kurucz (1993) model
atmospheres:
UVBLUE: Rodriguez-Merino et al. (2005)
Coverage: 3,000 to 50,000 K
850 to 4700 Å (R = 50,000)
-2.0 ≤ [Fe/H] ≤ +0.5
BLUERED: Bertone et al. (2008)
3500 to 7000 Å (R = 500,000)
Walcher (2009): VVDS data (grey shading) vs. models (contours)
Major improvement after including Tlusty,
Martins et al., and UVBLUE stellar atmosphere
models to complement MILES library in SSP modelling
(work in progress).
Another look at the
problem:
Pure Miles (black)
Extended Miles (red)
In the pure Miles case
intermediate Teff stars were
represented by hotter stars.
It is important to use a
stellar library as complete
as possible.
Ionizing photons:
Depend on Tlusty models
For SSP’s of
Z=0
0.0001
0.0004
0.001
0.002
0.004
0.008
0.017
0.040 (green)
0.070 (black)
Improvement over BaSeL
Atlas values (e.g. HeII)
UV spectral indices
Defined by e.g. Fanelli et al.,
can be computed directly
from the UV sed, the same
as in the visible range.
Z = 0.5 x Zo (blue)
1.0 x Zo (black)
2.5 x Zo (red)
Recent work on UV indices:
Maraston et al. (2008)
Chavez et al. (2009)
Problem 2:
Tracks should predict the right number of stars, at least in
most relevan evolutionary phases (e.g. TP-AGB):
NIR stellar sed’s
Evolutionary tracks and the mass of galaxies
Improving the NIR spectral range
IRTF library:
Infrared Telescope Facility Spectral Library (Cool Stars)
Rayner et al. (2009)
Stellar Models for C-stars:
Aringer et al. (2009)
Both represent big improvements over previous data sets.
AGB
candidates
from SAGE
LMC survey
(Srinavasan et al. 2009)
AGB candidates
from SAGE LMC
survey
Must take into account effects of
dusty envelope and mass loss.
Dusty code
Poster by González-Lopezlira et al.
AGB candidates
from SAGE LMC
survey
Must take into account effects of
dusty envelope and mass loss.
Dusty code
Poster by González-Lopezlira et al.
Evolutionary tracks and the mass of galaxies
Bertelli et al. (2008):
Z = 0, 0.0001, 0.0004, 0.001, 0.002, 0.004, 0.008, 0.017, 0
.040, 0.070
TP-AGB evolutionary prescriptions by:
Marigo & Girardi (2007): calibrated with MC clusters and star
counts
Bertelli et al (2008): extrapolate results from the Marigo and Girardi
prescription to different chemical content of the
stellar envelope. Hence they
are uncalibrated.
olor
Color evolution vs. MC cluster data
TP-AGB stars contribute
roughly 60% of K light in
the galaxy rest frame in the
redshift range from 3 to 8
TP-AGB
more
numerous,
brighter,
and redder
(240 vs 60
per 1
million Mo
cluster)
Inferred mass
in B and K
HUDF data
CB07
SSP’s
τ(V) = 0
t=0.6 – 1.3 Gyr
M11=0.09–0.25
HUDF data
CB07
SSP’s
τ(V) = 1
t=0.7 – 1.3 Gyr
M11 = 0.1 – 0.3
HUDF data
CB07
SSP’s
τ(V) = 3
t=0.7 – 0.9 Gyr
M11 = 0.1 – 0.5
Problem 3:
Why different codes produce different results?
Show example
All these models
are for the same
Z = 0.008 and
IMF (Salpeter)
LMC clusters
Different tracks
Different sed’s
Tracks Padova 2008,
Different Z’s
Stochastic effects
Large amount of work by many groups on:
Alpha-enhanced stellar and population models:
Vazdekis and collaborators;
Coelho and collaborators;
Maraston and collaborators;
Thomas and collaborators
Variable light/heavy element ratio stellar and population models:
Worthey and collaborators
Star formation history in large galaxy samples:
A legion of really bright and hard workers
The role of binaries
Vanbeveren, Zhanwen Han
Propagation of uncertainties in population synthesis models and
derived properties of galaxies:
Series of papers by Conroy, Gunn, & White
The future:
 The answers to distant galaxy problems will come from
understanding nearby stars
 We have collected more photons from distant galaxies than from
nearby stars
 Population synthesis models can get better only if ingredients get
better. Most of the uncertainties come from critical stages in the
evolutionary tracks or missing spectra of important stellar
evolutionary phases.
 This can happen both from the observational and the theoretical
framework
Basic things that we do not know well enough:

Distance to star clusters needed for calibration of stellar evolution
models to a higher precision than at present. These errors
translate into errors in the age of galaxies or other stellar
populations dated using synthesis models.

Physical properties of more stars distributted all over the HR
diagram: mass, Teff, radius, chemical abundance, chemical
anomalies…

Blue stragglers, origin and role in stellar evolution and relevance
in galaxies as integrated populations

The role of binaries in the evolution of stellar populations of
various ages and metallicities, and in different environments
(stellar density)
Basic things that we do not know well enough:

Evolutionary tracks or evolutionary prescription for EHB stars.
Frequency, lifetimes, dependence on metallicity

The role of mass loss.

Is the IMF universal?

Effects of dust

More complete stellar spectral libraries (HST ?) that fill the
current gaps (TP-AGB, EHB, Blue stragglers) in as wide a
wavelength range as possible and with a good flux calibration, or

Model stellar atmospheres that can be used instead of the
observed spectra mentioned in the previous point, including
complete line lists and the right geometry and kinematics
Basic things that we do not know well enough:

Can stellar rotation be neglected (as we always do)?

Up to what extent can multiple MS in “SSPs” be neglected?

Do light/heavy element ratios vary from star to star or galaxy to
galaxy in a way we can understand? Are models a la Worthey
really necessary?
IndoUS vs STELIB
HNGSL UV coverage
HNGSL (black) vs IUE
(cyan) and Kurucz
models (green)
Solar metallicity
12 Gyr SSP
Chabrier IMF
Padova 1994 tracks
HNGSL UV coverage
HNGSL (black) vs IUE
(cyan) and Kurucz
models (green)
Solar metallicity
500 Myr SSP
Chabrier IMF
Padova 1994 tracks
HNGSL UV coverage
HNGSL vs Kurucz
models (green)
Z = 0.2 x Solar (blue)
0.4 x Solar (cyan)
1.0 x Solar (red)
1 Gyr SSP
Chabrier IMF
Padova 1994 tracks
HNGSL in the visible range
HNGSL (black) vs
STELIB (red),
Kurucz models
(green), and Pickles
library (cyan)
Solar metallicity
12 Gyr SSP
Chabrier IMF
Padova 1994 tracks
Flux
calibration
problem in
IndoUS
library
Flux
calibration
problem in
IndoUS
library