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

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

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

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 (?)

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

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.

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?

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 !

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 ~150 000 independent spectra + Sa galaxies …

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])

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

SAURON - Indices 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

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

NGC 3384 S0 (cluster)

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

Emission line subtraction spectrum fit residual Emsellem et al.

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

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

NGC 4150 (S0) Only ±10 km/s

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

NGC 4150 (S0) : post-starburst

Metal production

Why abundance ratios? Timescales! The Sun

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

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

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

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

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