1. The SAURON Survey - The stellar populations of early-type galaxies
Harald Kuntschner
(ESO, Germany)
&
The SAURON team

2. Contents Introduction Goals with SAURON Examples of stellar pops
What do we know about stellar pops in E/S0s?
Goals with SAURON
Examples of stellar pops
Age, metallicity
Abundance ratios
Conclusions

3. Galaxy Formation When and how do E/S0/Sa galaxies form?
SAURON
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?
 Nicolas, Michele

4. What do we know?
Early-type galaxies are mostly found in high density regions
Luminous (massive) cluster E/S0 galaxies are redder (metal rich) – CMR relation
Stars in Es are old but S0s can have younger populations
… or could this be just a luminosity effect?
The pops of spiral bulges are similar to Es (?)
Field E/S0s are younger compared to cluster (?)

5. Field vs Cluster Field Cluster young old Only central observations
What about disk/bulge differences
Where are the young stars?
Kuntschner et al. 2002

6. What do we know? Clues from intermediate redshift
The Butcher Oemler effect:
z=0.5 galaxies are bluer than
galaxies in similar clusters at z=0.
In rich clusters, spiral galaxies are 2-3 times more common at z=0.5 than at z=0.
S0 galaxies are correspondingly less common.

7. What would we like to know?
As a function of luminosity,
Hubble type and environment
How were galaxies assembled? What are the ages & metallicities of their stellar populations?
Differences between components?
e.g., how common are young disks?
What is the connection between the kinematics and stellar populations of the galaxies?

8. Two complementary approaches
Investigating the fossil evidence in nearby galaxies – end products
High precision work !
Looking far away, i.e. back in time
Need for large telescopes (VLT, Gemini)
Need to match progenitors !

9. The SAURON Sample
Representative sample of 72 nearby E/S0/Sa (selected from a parent sample of 327)
cz < 3000 km/s
DEC: -6° < d < +64° and |b|  15°
MB  -18 mag (factor of 50 in luminosity)
24 E, 24 S0, 24 Sa (each 12 cluster, 12 field)
Current status:
72/72 (100%) galaxies observed
~ independent spectra
+ Sa galaxies …

10. Determining age and metallicity in practice
Determine strengths of absorption features
Correct them for e.g., velocity broadening of the galaxy
Compare them with theoretical line strengths f(age, Z, [Mg/Fe])

11. Models: age, metallicity & [Mg/Fe]
luminosity weighted
[Mg/Fe]
solar
Vazdekis 1999
Thomas et al. 2002

12. SAURON - Indices Hb – age sensitive
Fe5015 – metallicity and age sensitive
Mgb – metallicity and age sensitive
Fe good Fe indicator
Needed for [Mg/Fe]
[OIII] (emission feature)
Probing the ionized gas

13. Literature Comparisons
Line Strengths -
Literature Comparisons
NGC 3384
Major Axis
Long-Slit comparison
Minor Axis
à Fisher et al. 1997

14. NGC 3384 S0 (cluster)

15. Line-strength maps – N5813 H emission [OIII] emission H emission
de Zeeuw et al. MNRAS 329, 513

16. Emission line subtraction
spectrum
fit
residual
Emsellem et al.

17. NGC 4365 (E3) – Line-strength
Davies, Kuntschner, Emsellem, et al., 2001, ApJL, 548, L33
Clear KDC
Metal enrichment?
No sign of KDC!

18. The KDC is old and in line with main body
NGC 4365 – Age, [M/H]
The KDC is old and in line with main body
Centre
Co-rotating core
Body at core radius
Body at larger radii

19. NGC 4150 (S0)
Only ±10 km/s

20. NGC 4150 (S0)
Strong Hb in centre
Central dip in Mgb

21. NGC 4150 (S0) : post-starburst

22. Metal production

23. Why abundance ratios?
Timescales!
The Sun

24. NGC 4150 – [Mg/Fe] Solar abundance ratios for young (central) stars
Old, underlying stellar
population [Mg/Fe]>0
0.3

25. The KDC abundance ratio is in line with main body
NGC 4365 – [Mg/Fe]
The KDC abundance ratio is in line with main body

26. NGC 5813 – [Mg/Fe] KDC is old [Mg/Fe] = 0
0.0
0.4
KDC is old
[Mg/Fe] = 0
Small increase of [Mg/Fe] towards centre

27. NGC 4406 – [Mg/Fe] KDC is old [Mg/Fe] = 0
0.0
0.3
KDC is old
[Mg/Fe] = 0
Small increase of [Mg/Fe] towards centre

28. Line-strength measurements
Conclusions
Line-strength measurements
SAURON can measure highly accurate line-strength indices over a 2dim FoV
Line-Strength maps of E/S0s are largely ‘smooth’; iso-index contours follow roughly the isophotes
Individual galaxies do show line-strength structure
Abundance ratios are interesting probes of star-formation time-scales