Stellar population models with variable abundance ratios

Transcription

1 Stellar population models with variable abundance ratios Daniel Thomas University of Oxford Claudia Maraston (Oxford) Ralf Bender (MPE) Andreas Korn (Uppsala) Roger Davies (Oxford)

2 Outline o How to measure element abundance ratios o Inclusion in SSP models empirical vs theoretical α-enhancement at constant Z or constant Fe? sensitivity of Balmer line indices absorption index and element abundance role of α-enhanced tracks myth of Balmer line data below the grid o Summary

3 How to measure abundance ratios Star Element ratios Elliptical galaxy Absorption line index?

4 Ellipticals didn t fit TMB03 Worthey, Faber, González 1992; Davies, Sadler, Peletier 1993; Carollo & Danziger 1994; Fisher, Franx, Illingworth 1995; Bender & Surma 1995 Globular clusters: Maraston et al 2003

5 Role of the stellar tracks Element abundance variation Absorption lines Stellar evolution, opacities Lick indices Tripicco & Bell 1995 Korn, Maraston, Thomas 2005 Isochrones Salaris & Weiss 1998; Salasnich et al. 2000; Kim et al Colors, Lick indices Weiss et al. 1995; Maraston et al. 2003; Thomas & Maraston 2003

6 Element ratio semi-empirical effects in SSP models semi-theoretical Empirical Theoretical fitting functions stellar libraries well calibrated limited parameter space model atmosphere calculations endless parameter space poorly calibrated Mg 1

7 Climbing up the isochrone I SSP = j I * j f * c, j f ( T,log g, [ Z / H] ) eff I * j stellar libraries Thomas, Maraston, Bender 2003 Worthey et al 1994

8 Climbing up the isochrone I SSP = j I * j f * c, j f ( T,log g, [ Z / H ] ) eff I I * j [ X ] i stellar atmospheres libraries Thomas, Maraston, Bender 2003 Korn, Maraston, Thomas 2005 Tripicco & Bell 1995; Trager et al 2000

9 Korn et al response functions

10 Calibration with globular clusters

11 Calibration with globular clusters

12 The solar mix H He H He Z Z Carbon Fe Oxygen O α-elements al a C

13 Index responses in detail

14 Calibration with globular clusters Thomas, Maraston, Korn (2004); Korn, Maraston, Thomas (2005)

15 Balmer ages consistent with χ 2 Thomas & Davies 2006 Data: Proctor & Sansom 2002

16 Absorption index and element abundance Since the method of response function is complex and introduces unknown systematic errors we did not use it. We therefore adopted a more straightforward method using the Balmer-metal index diagrams. [ ] et al 2006 Galaxy

17 α/fe over-estimated

18 Effect of alpha-enhanced tracks Maraston et al 2003

19 All the effort in vain? α-enhanced track Salasnich et al solar-scaled track Thomas & Maraston 2003

20 Maybe not Galaxies older than the Universe!!! α-enhanced track Salasnich et al 2000 solar-scaled track

21 Data below the grid: quality matters Maraston et al 2003 VLT Keck Brodie et al 2005 Keck Puzia et al 2004 Conselice 2005

22 Summary o Element abundance ratios in SSP models Empirical vs theoretical semi-empirical Absorption index and element ratios need reponse fct. Constant Z or Fe? α-enhancement is Fe depletion Sensitivity of Balmer line indices α/fe ratio Role of α-enhanced tracks too blue still a lot to do Balmer data below the grid observer s fault