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Stellar population properties of bulges Daniel Thomas Max-Planck-Institut für extraterrestrische Physik, Garching Stellar population properties  star.

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Presentation on theme: "Stellar population properties of bulges Daniel Thomas Max-Planck-Institut für extraterrestrische Physik, Garching Stellar population properties  star."— Presentation transcript:

1 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

2 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

3 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

4 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

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

6 Calibration Horizontal branch Morphology (Maraston & Thomas 2000)

7 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?

8 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)

9 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?

10 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?

11 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

12 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

13 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

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

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

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

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

18 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

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

20 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

21 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

22 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

23 Proctor, Sansom, Reid, 2000

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


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