THE "SHY" SIDE OF GALAXIES AS REVEALED BY STEMAGE

Co-fundedby
theEuropeanUnion
viaFP7CareerIntegra:onGrant
SteMaGE
www.arcetri.astro.it/~zibe4/SteMaGE
THE "SHY" SIDE OF GALAXIES AS REVEALED
BY STEMAGE-CALIFA 3D ANALYSIS
RESULTS FROM A SPATIALLY RESOLVED SPECTROPHOTOMETRIC ANALYSIS
OF STELLAR MASS IN THE CALIFA SURVEY
Stefano Zibetti (INAF-Osservatorio Astrofisico di Arcetri)
in collaboration with Anna Gallazzi, Stéphane Charlot,
the CALIFA Collaboration
GEE4 — DISSECTING GALAXY EVOLUTION
UNVEILING GALAXY ASSEMBLY HISTORY
WITH SPATIAL AND SPECTRAL HIGH-RESOLUTION OBSERVATIONS
30.11-2.12.2015, Napoli
STEMAGE PROJECT - MOTIVATION
Stellar mass is a key property/driver of galaxy evolution
Need to measure it as accurately as possible:
to measure its build-up, distribution in galaxies and in the intergalactic
space, over the cosmic time
to understand scaling relations and their evolution
to quantify dynamical effects inside galaxies
Accuracy at 10% level is desirable: is it actually attainable?
Stefano Zibetti - GEE4 - Napoli - 30/11-2/12/2015
M* FROM STELLAR POPULATION ANALYSIS:
FOCUS PROBLEMS
(THERE ARE MANY OTHERS!)
Even if we knew stellar evolution and IMF perfectly well (and
we don’t!), keep in mind that:
Light is not a linear tracer of stellar mass, although light is
what we rely on
To reliably estimate stellar mass from starlight (VIS-NIR) we
need to constrain to some level:
the star-formation and chemical enrichment history of a
composite stellar population (see e.g. Gallazzi & Bell, 2009)
the properties of dust and the relative distribution of dust
and stars
M/L variations
up to 1dex!
Galaxies are (often) very inhomogeneous: need to properly
weigh different regions (see e.g. Zibetti, Charlot & Rix, 2009 ZCR09)
M/L
Stefano Zibetti - GEE4 - Napoli - 30/11-2/12/2015
OBJECTIVES
Create a benchmark of optimally measured stellar masses on a sample of galaxies
that offers:
good quality optical spectroscopy to nail down SFH and metallicity
multi-band imaging, to constrain dust attenuation
spatial resolution (scales ~kpc) not to miss any (dim) component
I. Quantify biases arising in larger surveys from:
lack of complete information (e.g. no spectroscopy available)
lack of spatial resolution (check results from ZCR09)/ limited spatial sampling
assumptions in the models (chiefly SF and ChEn Histories, dust)
I1. Calibrate “cheaper” M* estimators (e.g. color-M/L relations)
Note: Use of resolved regions allows us to test more “extreme” conditions than
galaxies as a whole
Stefano Zibetti - GEE4 - Napoli - 30/11-2/12/2015
EXPERIMENTAL SETUP
Dataset: 332 best quality CALIFA (pre-DR3,
Sanchez+12, 16 in prep.) + SDSS:
all morphologies, >500,000 spaxels full optical
range spectra, ~kpc resolution
Models: new Monte Carlo Stellar
Population Synthesis libraries with
500,000 models:
BC03 SSPs, Chabrier IMF
SFH: á la Sandage (1986,
Gavazzi et al. 2002), variable
age, variable tau, bursts
Generalised leaking box model
for metal enrichment history
(adapted from Erb 2006)
2-component dust á la Charlot
& Fall (2000)
Stefano Zibetti - GEE4 - Napoli - 30/11-2/12/2015
NGC 0001
SDSS-g full res.
METHOD
SDSS-g CALIFA res.
• CALIFA-SDSS
Spaxel-by-spaxel consistently measure:
• 5 stellar absorption indices
(D4000n, Hβ, Hγ+Hδ, [Mg2Fe],
[MgFe]’ as in Gallazzi et al. 2005)
AND
• 5 broadband photometric fluxes
(SDSS ugriz)
• Bayesian parameter estimation:
compare observables with each model
⟹ likelihood function ⟹ posterior Probability Distribution
Function
⟹ marginalisation
•
Stefano Zibetti - GEE4 - Napoli - 30/11-2/12/2015
ve
Adapti
ing
smooth
match: resample & PSF match
CALIFA-g synthetic
• Adaptive smoothing for optimal SNR>20 [10]/pix:
azmooth3C
SNR after adaptive
• Stellar continuum-nebular line decoupling
smoothing
(customized GANDALF+pPXF) spaxel by spaxel
SDSS-g final res.
DOES IT WORK WELL?
NGC1056: one of the most difficult cases: distinct SPs, heavy dust
SDSS matched to CALIFA
M*
M/L
SDSS original resolution
More than words, one
example:
dust lanes properly
“corrected”, smooth
mass distribution
Ag
Stefano Zibetti - GEE4 - Napoli - 30/11-2/12/2015
RESOLUTION EFFECTS: IS THE INTEGRATED LIGHT
REPRESENTATIVE OF THE SUM OF A GALAXY’S PARTS?
Compare:
M* as the sum
of M* in each
spaxel (resolved
estimate)
vs
M* as derived
from integrated
spectrophotometry
(unresolved
estimate)
Note: within
Stefano Zibetti - GEE4 - Napoli - 30/11-2/12/2015
RESOLUTION EFFECTS: IS THE INTEGRATED LIGHT
REPRESENTATIVE OF THE SUM OF A GALAXY’S PARTS?
Compare:
M* as the sum
of M* in each
spaxel (resolved
estimate)
vs
M* as derived
from integrated
spectrophotometry
(unresolved
estimate)
Note: within
Stefano Zibetti - GEE4 - Napoli - 30/11-2/12/2015
RESOLUTION EFFECTS: IS THE INTEGRATED LIGHT
REPRESENTATIVE OF THE SUM OF A GALAXY’S PARTS?
Compare:
M* as the sum
of M* in each
spaxel (resolved
estimate)
vs
M* as derived
from integrated
spectrophotometry
(unresolved
estimate)
Note: within
Stefano Zibetti - GEE4 - Napoli - 30/11-2/12/2015
RESOLUTION EFFECTS: IS THE INTEGRATED LIGHT
REPRESENTATIVE OF THE SUM OF A GALAXY’S PARTS?
Compare:
M* as the sum
of M* in each
spaxel (resolved
estimate)
vs
M* as derived
from integrated
spectrophotometry
(unresolved
estimate)
Note: within
Stefano Zibetti - GEE4 - Napoli - 30/11-2/12/2015
WHY RESOLUTION EFFECTS?
ARP220
Lig
by ht w
glo ei
ba ght
l M ed
Lig /L by ht w
lo eig
ca h
l M te
/L d M*
M/L from integrated light
↓
M/L
Ag
Low-M/L regions outshine the highM/L regions (obscured by dust) and
pull down the global M/L estimate
Stefano Zibetti - GEE4 - Napoli - 30/11-2/12/2015
WHY RESOLUTION EFFECTS?
M*
Lig
by ht w
glo ei
ba ght
l M ed
/L Lig
by ht w
lo eig
ca h
l M te
/L d UGC10205
M/L from integrated light
↓
M/L
Ag
Low-M/L regions outshine the highM/L regions (obscured by dust) and
pull down the global M/L estimate
Stefano Zibetti - GEE4 - Napoli - 30/11-2/12/2015
RESOLUTION EFFECTS
Compare:
M* as the sum
of M* in each
spaxel (resolved
estimate)
vs
M* as derived
from integrated
spectrophotometry
(unresolved
estimate)
Catastrophic “failures”:
dusty systems
Note: within
Stefano Zibetti - GEE4 - Napoli - 30/11-2/12/2015
RESOLUTION EFFECTS
Compare:
M* as the sum
of M* in each
spaxel (resolved
estimate)
vs
M* as derived
from integrated
spectrophotometry
(unresolved
estimate)
Catastrophic “failures”:
dusty systems
Note: within
Stefano Zibetti - GEE4 - Napoli - 30/11-2/12/2015
WHY RESOLUTION EFFECTS?
SDSS original resolution
Lig
by ht w
glo ei
ba ght
l M ed
/L M*
M/L
Ag
Lig
by ht w
lo eig
ca h
l M te
/L d NGC0932
M/L from integrated light
↓
Low-M/L regions (young stars)
outshine the high-M/L regions (old
stars) and pull down the global M/L
estimate
Stefano Zibetti - GEE4 - Napoli - 30/11-2/12/2015
RESOLUTION EFFECTS
Compare:
M* as the sum
of M* in each
spaxel (resolved
estimate)
vs
M* as derived
from integrated
spectrophotometry
(unresolved
estimate)
Classical effect:
young stars outshining old stars
Catastrophic “failures”:
dusty systems
Note: within
Stefano Zibetti - GEE4 - Napoli - 30/11-2/12/2015
RESOLUTION EFFECTS
Compare:
M* as the sum
of M* in each
spaxel (resolved
estimate)
vs
M* as derived
from integrated
spectrophotometry
(unresolved
estimate)
Classical effect:
young stars outshining old stars
Catastrophic “failures”:
dusty systems
Note: within
Stefano Zibetti - GEE4 - Napoli - 30/11-2/12/2015
WHY RESOLUTION EFFECTS?
SDSS original resolution
UGC10043
Lig
by ht w
glo ei
ba ght
l M ed
/L M*
M/L
Ag
Age
Lig
by ht w
lo eig
ca h
l M te
/L d M/L from integrated light
↓
High-M/L regions (old bulge
stars and heavily obscured
stars in the centre) dominate
the light; moderately high-M/L
regions (moderately obscured
young stars in the disc) do not
compensate
Occurs in edge-on discs!
Stefano Zibetti - GEE4 - Napoli - 30/11-2/12/2015
RESOLUTION EFFECTS
Compare:
M* as the sum
of M* in each
spaxel (resolved
estimate)
Edge-on discs:
combined effect of old stars and
obscuration of young stars
vs
M* as derived
from integrated
spectrophotometry
(unresolved
estimate)
Classical effect:
young stars outshining old stars
Catastrophic “failures”:
dusty systems
Note: within
Stefano Zibetti - GEE4 - Napoli - 30/11-2/12/2015
DO WE CARE ABOUT
RESOLUTION EFFECTS?
Roughly 10% of the
Universe’s stellar mass
budget (based on 332
galaxies, volume uncorrected
CALIFA pre-DR3 sample,
554,698 spaxels) is “LOST”
due to resolution effects
Note however that we’re
limited to the bright regions
well within the optical radius!
Stefano Zibetti - GEE4 - Napoli - 30/11-2/12/2015
Filled histogram: mass based on local M/L (“resolved”)
Empty histogram: mass based on global M/L (“unresolved”)
CONCLUSIONS
†
Galaxies are complex and measuring their mass can be quite inaccurate if we cannot resolve
their subcomponents/structure
Neglecting this may lead to errors up to few 0.1 dex
worse cases:
messy dusty systems and old galaxies with young “frosting”: unresolved estimates are
biased low
edge-on late-type spirals: unresolved estimates are biased high
Typically and on average the blue-stars-outshining-red-stars effect prevails (in agreement with
previous claims, ZCR09, Wuyts+12), but in edge-on galaxies the reverse occurs
Average effect on stellar mass census is of the order of a few 10% missing if unresolved
estimates are used
Difficult to provide recipes to correct — account for a “structural” error budget in
unresolved M*-estimates of ~20% on average, much more for more inhomogeneous/dusty
systems (not all galaxies have the same error!).
†
#premioGAC
Stefano Zibetti - GEE4 - Napoli - 30/11-2/12/2015