Stellar population properties of bulges

Daniel ThomasMax-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 ThomasMax-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

Reviewof

Chemical enrichment

SNII Mg, FeSNIa Fe

Enrichment ofIron is delayed

Supernova Ia

Elliptical galaxies

Thomas, Maraston, Bender 2002Trager et al. 2000

Thomas, Greggio, Bender 1998Greggio & 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 www.mpe.mpg.de/~dthomas

New stellar population model

Stellar model atmosphere calculations

Cou

rtesy

: A

. K

orn

Tripicco & Bell 1995; Korn, Maraston, Thomas, in preparation

Calibration

Horizontal branchMorphology

(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-enhancedlike 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”

Jablo

nka

et a

l. 1996

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 toellipticals

Index gradients independent of Hubble type

“Less compatible with secularevolution model”

Preliminary, qualitative data analysisData 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 bulgeslower than ellipticals

“Sharp differences between early andlate types”

Mass-metallicity relation only for bulges

Disk contamination unclear, no gradientsSecular evolution not discussed

Data: Proctor & Sansom 2002Index-index diagramsE

S0S0aSaSabSbSbc

Contamination of line indices

Puzia, Kissler-Patig, Thomas, et al. 2003

Calibration with globular clusters

Thomas, Maraston, Korn 2004, MNRAS Letters, in press

Data

: Mara

ston

et a

l. 20

03

Data: Proctor & Sansom 2002

ES0S0aSaSabSbSbc

[α/Fe]

0.00.3

MWBulge

Index-index diagrams

Hß, Mgb, Fe5270, Fe5335HδA, Mgb, Fe5270, Fe5335Proctor & Sansom 2002

Data: Proctor & Sansom 2002Correlations with σE

S0S0aSaSabSbSbc

HδA, Mgb, Fe5270, Fe5335

MW Bulge

Blue bulges at high-z

Ellis, Abraham, Dickinson 2001

Secular evolution Disk contamination

Without Disk Disk material

Central valuesand 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, Fe5335HδA, Mgb, Fe5270, Fe5335Proctor & Sansom 2002

Comparison with EsE

S0S0aSaSabSbSbc

HδA, Mgb, Fe5270, Fe5335

MW Bulge

Ellipticals

Data

: Gon

zále

z 1993;

Beuin

g e

t al. 2

00

2;

Mehle

rt et a

l. 2003

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. 2003Saglia, Maraston et al. 2000

No age gradient in ellipticals