Stellar population properties of bulges

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
Review of

• 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

3
Chemical enrichment
SNII ? Mg, Fe SNIa ? Fe
Enrichment of Iron is delayed
Solar neighbourhood
Elliptical galaxies
Thomas, Maraston, Bender 2002 Trager et al. 2000
Thomas, Greggio, Bender 1998 Greggio Renzini
1983
4
New stellar population model

• 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

Calibration Maraston, Greggio, Renzini et al.
2003, AA
5
Stellar model atmosphere calculations
Courtesy A. Korn
Tripicco Bell 1995 Korn, Maraston, Thomas, in
preparation
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Calibration

Horizontal branch Morphology (Maraston Thomas
2000)
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Stellar populations of bulges and disks

• a/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)

• Bulges in later type spirals have steeper
  
• color gradients and are younger
• (optical/NIR color maps Balcells Peletier
  
• 1994 Peletier et al. 1999)

• ? 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)

9
Previous work (FP)

• ? Major sequence defined by ellipticals and
  bulges in ?-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 s-profiles (Falcón-Barroso et al.
2003b)
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-s like ellipticals
• (Saglia et al. 2002 Falcón-Barroso et al. 2003)

• 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

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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 gt 1 Re
• ? Galaxy type from S0 Sc, wavelength range
  3900 ? 5500 Å
• ? Ages and Mg/Fe ratios similar to
• ellipticals
• ? Index gradients independent of
• Hubble type
• ? Less compatible with secular
• evolution model

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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 ? 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

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Index-index diagrams
Data Proctor Sansom 2002
E S0 S0a Sa Sab Sb Sbc
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Contamination of line indices
Puzia, Kissler-Patig, Thomas, et al. 2003
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Calibration with globular clusters
Data Maraston et al. 2003
Thomas, Maraston, Korn 2004, MNRAS Letters, in
press
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Index-index diagrams
Data Proctor Sansom 2002
E S0 S0a Sa Sab Sb Sbc
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Correlations with s
Data Proctor Sansom 2002
E S0 S0a Sa Sab Sb Sbc
MW Bulge
Proctor Sansom 2002
HdA, Mgb, Fe5270, Fe5335
Hß, Mgb, Fe5270, Fe5335
HdA, Mgb, Fe5270, Fe5335
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Blue bulges at high-z
Ellis, Abraham, Dickinson 2001
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Secular evolution
Disk contamination

• Central values edge-on
• MW bulge fits in
• No correlation with
• Hubble type
• - lt 10 effect

• Bureaus talk
• No correlation with
• Hubble type

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Comparison with Es
E S0 S0a Sa Sab Sb Sbc
MW Bulge
Proctor Sansom 2002
HdA, Mgb, Fe5270, Fe5335
Hß, Mgb, Fe5270, Fe5335
HdA, Mgb, Fe5270, Fe5335
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Conclusions

• Stellar population models taking element
  abundance
• ratios into account
• ? a/Fe ratios, ages from H?, Hd
• Emission contamination important issue
• ? use higher-order Balmer lines TMB models
• Bulges have younger ages and lower a/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

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Proctor, Sansom, Reid, 2000
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Stellar Population Gradients
No age gradient in ellipticals
Mehlert, Thomas et al. 2003 Saglia, Maraston et
al. 2000