Stellar population properties of bulges Daniel Thomas Max-Planck-Institut für extraterrestrische Physik, Garching Stellar population properties  star formation episodes Current status in the literature  Imaging, structural parameters, Fundamental Plane  Absorption line index diagnostics Ages and element ratios along the Hubble sequence  Continuity from elliptical galaxies to bulges?  Fingerprints of secular evolution? Conclusions

Stellar population properties of bulges Daniel Thomas Max-Planck-Institut für extraterrestrische Physik, Garching Stellar population properties  star formation episodes Current status in the literature  Imaging, structural parameters, Fundamental Plane  Absorption line index diagnostics Ages and element ratios along the Hubble sequence  Continuity from elliptical galaxies to bulges?  Fingerprints of secular evolution? Conclusions Review of

Chemical enrichment SNII  Mg, Fe SNIa  Fe Enrichment of Iron is delayed Supernova Ia Elliptical galaxies Thomas, Maraston, Bender 2002 Trager et al Thomas, Greggio, Bender 1998 Greggio & Renzini 1983 Solar neighbourhood

Calibration: Maraston, Greggio, Renzini et al. 2003, A&A Thomas, Maraston, Bender, 2003a, MNRAS, 339, 897 Based on Maraston (1998) Fuel consumption theorem (Renzini & Buzzoni 1986) Stellar atmosphere calculations (Tripicco & Bell 1995; Korn, Maraston, Thomas in prep.) Extension of method introduced by Trager et al. (2000) Abundance ratio effect “semi-theoretically” included New stellar population model

Stellar model atmosphere calculations Courtesy: A. Korn Tripicco & Bell 1995; Korn, Maraston, Thomas, in preparation

Calibration Horizontal branch Morphology (Maraston & Thomas 2000)

Stellar populations of bulges and disks  α/Fe and age as tracer of star formation  secular evolution as star formation  Bulge properties as function of spiral type  bulge versus disk  role of secular evolution  Bulges versus elliptical galaxies  are bulges small ellipticals?

Previous work (Imaging)  Fainter bulges in later spirals have exponential profiles (WFPC2 F606W; Carollo et al. 1998)  Bulges of in later spirals more elongated (NICMOS H-band images; Fathi & Peletier 2003) Recent star formation in later-type bulges? Fingerprints of secular evolution?  Bulges in later type spirals have steeper color gradients and are younger (optical/NIR color maps; Balcells & Peletier 1994; Peletier et al. 1999)

Previous work (FP)  Major sequence defined by ellipticals and bulges in κ-space, bulges below the FP (Bender et al. 1992)  Offset to FP more pronounced in bulges of late-type spirals (Falcón-Barroso et al. 2002)  Flattened bulges in later-type spirals have shallower σ-profiles (Falcón-Barroso et al. 2003b) Bulges in earlier type spirals old like ellipticals. Bulges in later type spirals younger  secular evolution?

Previous work (absorption line indices)  Bulges are Mg/Fe-enhanced like elliptical galaxies (Fisher et al. 1995; Idiart et al. 1996; Jablonka et al. 1996; Casuso et al. 1996)  CaT-σ like ellipticals (Saglia et al. 2002; Falcón-Barroso et al. 2003) “Negligible influence of disk material” Jablonka et al  Cases of low Mg/Fe + younger age (Bender & Paquet 1995; 1999) Secular evolution in S0s?

Current work (absorption line indices)  Trager & Dalcanton (2001, AAS) “Determine metallicity and age in order to follow the hypothesis that late-type bulges form from disk instabilities.”  Sauron collaboration + M. Carollo Analysis and data unpublished

Current work (absorption line indices)  Gorgas, Jablonka, Goudfrooij (1999, 2002)  28 edge-on spirals, 4h per object on 4m  4” off from center avoiding dust lanes, gradients up to > 1 Re  Galaxy type from S0 – Sc, wavelength range 3900 ≤ λ ≤ 5500 Å  Ages and Mg/Fe ratios similar to ellipticals  Index gradients independent of Hubble type  “Less compatible with secular evolution model” Preliminary, qualitative data analysis Data unpublished

Current work (absorption line indices)  Proctor & Sansom (2002, MNRAS)  32 objects (11 Es, 6 S0s, 16 bulges)  Exposure ≤ 1h per object on 4m  Edge-on, minor axis, avoiding dust lanes  Galaxy type from S0 – Sbc  Wavelength range 4000 ≤ λ ≤ 5500 Å  Balmer indices corrected for emission  Ages and Mg/Fe ratios of bulges lower than ellipticals  “Sharp differences between early and late types”  Mass-metallicity relation only for bulges Disk contamination unclear, no gradients Secular evolution not discussed

Data: Proctor & Sansom 2002 Index-index diagrams E S0 S0a Sa Sab Sb Sbc

Contamination of line indices Puzia, Kissler-Patig, Thomas, et al. 2003

Calibration with globular clusters Thomas, Maraston, Korn 2004, MNRAS Letters, in press Data: Maraston et al. 2003

Data: Proctor & Sansom 2002 E S0 S0a Sa Sab Sb Sbc [α/Fe] MW Bulge Index-index diagrams

Hß, Mgb, Fe5270, Fe5335 HδA, Mgb, Fe5270, Fe5335 Proctor & Sansom 2002 Data: Proctor & Sansom 2002 Correlations with σ E S0 S0a Sa Sab Sb Sbc HδA, Mgb, Fe5270, Fe5335 MW Bulge

Blue bulges at high-z Ellis, Abraham, Dickinson 2001

Secular evolutionDisk contamination Without DiskDisk material Central values and gradients like ellipticals Young centers, positive gradients unlike ellipticals + Central values edge-on - MW bulge fits in - No correlation with Hubble type - < 10 % effect + Bureau’s talk - No correlation with Hubble type

Hß, Mgb, Fe5270, Fe5335 HδA, Mgb, Fe5270, Fe5335 Proctor & Sansom 2002 Comparison with Es E S0 S0a Sa Sab Sb Sbc HδA, Mgb, Fe5270, Fe5335 MW Bulge Ellipticals Data: González 1993; Beuing et al. 2002; Mehlert et al Thomas, Maraston, Bender 2002

Conclusions  Stellar population models taking element abundance ratios into account  α/Fe ratios, ages from Hγ, Hδ  Emission contamination important issue  use higher-order Balmer lines + TMB models  Bulges have younger ages and lower α/Fe than ellipticals  well-defined relations with velocity dispersion  continue relationship of elliptical galaxies  no trend with Hubble type  Gradients key to understand the role of the disk

Proctor, Sansom, Reid, 2000

Stellar Population Gradients Mehlert, Thomas et al Saglia, Maraston et al No age gradient in ellipticals