Transcript Density waves in the central regions of galaxies

3D spectrography
III - The SAURON Survey
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Introduction
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Dynamical evolution ?
– Impossible to really disentangle the chemical and
dynamical evolution in a galaxy…
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Introduction
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Cosmological context:
– Hierarchical building of the structures
Lacey 1992
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Introduction
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Cosmological context:
Numerical simulations
Density fluctuations:
/ =  << 1
P(δ) = (2π)-1/2 /σ(M) exp[ -δ2/2σ2(M)]
Press & Schechter (1974)
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Introduction
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Cosmological context:
– Inhomogeneous distribution
– Evolution with redshift
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Introduction
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Cosmological context:
– Interactions, harassment, mergers
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Galaxy
Formation
SAURON
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When and how do E/S0/Sa galaxies form?
– What is the orbital make-up of E/S0s?
– What is the average age?
– What is the average metal content?
– Origin of substructures; e.g. faint disks in Es,
decoupled cores, etc.
– E  S0  Sa transformations ?
– What is the relationship between global properties
and supermassive black holes ?
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Aims of the SAURON Survey
For a representative sample of nearby E/S0/Sa:
 Measure intrinsic shapes
 Determine velocity distribution (stars+gas)
 orbital make-up  Schwarzschild modelling
 Determine metallicity and age distribution
 Determine frequency of kinematically decoupled
structures and black holes
 Unravel the stellar population – kinematics
connection
Ideal tool: integral field spectrographs
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Ingredients
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A team
with relevant expertise in
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Funds
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Total 600 k€
From NL, F and UK
A unique instrument
an IFU with
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Integral field spectroscopy
Data reduction
Modelling
Dynamics and population of early-type galaxies
Large field of view
High throughput (20%, everything included)
Efficient data reduction pipeline
Telescope time
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~54 nights of 4.2m WHT over 3 years
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SAURON
Spectroscopic
Areal
Unit
for Research
on Optical
Nebulae
• Bacon et al. 2001, MNRAS 326, 23
• de Zeeuw et al. 2002, MNRAS 329, 513
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SAURON versus OASIS
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Larger field of view
– Sampling ~1"  f/1.8
camera (oasis f/3)
Simultaneous sky
– 1.9' from object
Spectrum length
– 580 pixels (OASIS 360)
 spectra more densely
packed
Number of spectra
– 1577 including 146 for the
sky
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Specifications
Telescope
William Hershell (4.2 m)
Sampling
0.94 x 0.94 arcsec (LR)
0.27 x 0.27 arcsec (HR)
Field of view
33 x 41 arcsec (LR)
9 x 11 arcsec (HR)
Lenslets
1577 (146 sky)
Wavelength range
4810-5350 Å
Spectral features
Hb, [OIII], Mgb, Fe5270
Instrumental resolution
~ 110 km/s
Total Efficiency
14.7 %  > 20% (VPH)
Commissioned
February 1999 (at WHT)
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Data Reduction
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Goal is to produce uniform and high quality reduced data
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Inherit from the experience gained with TIGER and OASIS
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Specific developments :
– To take into account the denser packing of the SAURON
spectra
– To mosaic and merge exposures
– To efficiently reduce a large amount of data
– 2D binning
– Pipeline and database
– More analysis tools
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The Sample
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Representative sample of
72 nearby E/S0/Sa galaxies
cz < 3000 km/s
DEC: -6° < d < +64° and |b|
 15°
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MB  -18 mag (factor of 50
in luminosity)
24 E, 24 S0, 24 Sa (12
cluster, 12 field)
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The Sample
Status :
Survey completed in April 2002
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7 observing runs
71/72 galaxies observed + 10 “specials”
> 160 000 independent spectra!
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Complementary Data
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The nucleus
– Imaging
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HST WFPC2
– A large fraction available in archive
– Spectrography
 OASIS/CFHT observations
– Completed in April 2002 (20 nights)
 A few STIS observations
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The extended halo
– Ground-based imaging
– Long slit observations
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Up to 2 re
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Science Verification
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Science Verification
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Photometry
– Is photometry preserved in the
reconstructed images ?
– Comparison with HST
photometry
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Dµv = 0.016
De = 0.012
DPA = 1°
NGC 4365
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Science Verification
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Stellar kinematics
– NGC 3384
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Major
Minor
SAURON 2h
Fisher 97, 2" slit
Dv=7 km.s-1
Ds=6 km.s-1
Dh3=0.015
Dh4=0.015
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Science Verification
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Line strength
– NGC 3384
– Long slit, Fisher et al
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D(Hb) = 0.1 A
D(Mgb) = 0.1A
D(Fe5270) = 0.1A
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Science Verification
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Emission Lines
– NGC 5813, SAURON 2 x 1h mosaic
– Long slit Caon et al
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Dv([OIII]) ~15 km.s-1
– Continuum subtraction is critical
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Science Verification
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Conclusion
– SAURON achieve equivalent or better data quality
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Absorption lines studies
– Stellar kinematics, up to h4
• Precision : 6-7 km.s-1 (1/17 of resolution)
– Line index
• Precision : 0.1 A
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Emission line studies
– Morphology and flux
– Kinematics
– But SAURON is 2D !!
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Photometric accuracy better than 2%
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Stellar Kinematics
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SAURON I,V,s Maps
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'Axisymmetric' objects ?
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Kinematics axis aligned with photometric axis
'Normal' rotator ? (but see later in the talk…)
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‘Non-axisymmetric' objects
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Misalignement of photometric and kinematical
axis
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Complex Dynamics
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Is photometry the good
indicator ?
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Stellar kinematical maps are richer than light
distribution
Bacon et al. 2001, de Zeeuw et al. 2002, Emsellem et al. 2003
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Stellar populations
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What would we like to know?
As a function of luminosity,
Hubble type and environment.
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How common are (young?) disks in ellipticals?
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How were galaxies assembled? What are the ages &
metallicities of their stellar populations?
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What is the connection between the kinematics and stellar
populations of the galaxies?
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SAURON –
Stellar Population Goals
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Probe the star-formation history
• Age of stars (luminosity weighted)
• Metallicity of stars (luminosity weighted)
• Abundance ratios (e.g. [Mg/Fe]),
• i.e. probe star-formation time-scales
Unravel the stellar population – kinematics connection
(coloured orbits)
SAURON:
• Delivers unprecedented quality, uniformity
• 2-D distribution
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SAURON - Indices
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Hb – age sensitive
Fe5015 – metallicity and age sensitive
Mgb – metallicity and age sensitive
Fe5270 -- good Fe indicator
Needed for [Mg/Fe]
[OIII] (emission feature)
Probing the ionized gas (also Hb!)
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The Vazdekis (1999) models
Problems with the Lick system:
• Resolution low, so few features can be analysed
• Not flux calibrated
• Corrections for velocity broadening difficult
• Measurements of Lick stars based on a non-linear detector
Vazdekis (1999)
stellar library of Jones (1997)
 Spectral resolution 1.8 A (FWHM) (Lick 9A)
 "latest” isochrones, photometric libraries
 Predict full spectra, rather than indices
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3856-4476 A and 4795-5465 A (all we need)
Ability to define new indices (Sauron Fe5270, Hb+)
Spectral fitting of two populations (difficult!)
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Model comparison
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Absorption line subtraction
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Emission Lines - NGC 5813
comparison with
Caon et al. (2000)
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Line Strengths in NGC 5813
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A few examples
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NGC 7742 (Sb/field)
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NGC 4314 (S/cluster)
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POSS, 7' x 7'
SAURON, Intensity
NGC 3623
(S/cluster)
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NGC 3377 (E!!/cluster)
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NGC 5866 (special)
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NGC 4698 (S/cluster)
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Kinematically Decoupled Cores
(KDC)
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KDC – ‘morphology’
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Central location
 Varying rotation
speeds (60-100 km/s)
 Misalignments of
- KDC with phot axis
- Zero velocity curve
with phot axis
When did the
KDCs form?
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NGC 4365 (E3) – Line-strength
Clear KDC
Metal enrichment? No sign of KDC!
Davies, Kuntschner, Emsellem, et al., 2001, ApJL, 548, L33
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NGC 4365 – Age, [M/H]
The KDC is old and in line
with main body
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NGC 4150 (S0/cluster)
Only
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±10 km/s
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NGC 4150 (S0) : post-starburst
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Summary
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The stellar kinematics of early-type galaxies exhibit a rich
variety of structures
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Axisymmetry is the exception rather than the rule
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The view we have from galaxy photometry is misleading
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The view we have from major and minor axis kinematics is too
restricted
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Have we found the tracer of the complex history of galaxy
formation and evolution ?
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Summary
KDC
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KDC Frequency 15% … awaiting full sample
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Misalignments of kinematic and photometric axis for KDC and
main body  triaxial structure?
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3/4 KDC show old stellar populations, perhaps increased
metallicity & abundance ratios
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Kinematic arrangement stable over a long time for old KDCs
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Conclusions
SAURON+OASIS+HST+gd-based Imaging =
a unique atlas to probe the formation and evolution processes
of early-type galaxies
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Adapted tools for the analysis
(MGE, 2D binning, kinemetry, Schwarzschild, “coloured Nbody”, new stellar libraries, …)
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Further readings
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SAURON papers:
– Bacon et al. 2001, MNRAS 326, 23
– Davies, Kuntschner, Emsellem, et al., 2001, ApJL, 548, L33
– de Zeeuw, Bureau, Emselle, et al. 2002, MNRAS 329, 513
– Verolme et al. 2002 & 2003, McDermid, et al., …
– Emsellem et al. 2003, to be submitted soon
http://www.strw.leidenuniv.nl/sauron/
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