Secular Evolution and Stellar Populations

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Secular Evolution and Stellar Populations
Reynier Peletier Kapteyn Institute Groningen
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Secular evolution and stellar populations a
critical look at early-type bulges

1. Some colour maps of early-type bulges
2. The Ca II IR triplet in early-type bulges
3. Bulges on the fundamental plane of early-type
   galaxies
4. SAURON line strength maps of early-type bulges

Collaborators (1) M. Balcells (2 and 3) M.
Balcells, J. Falcón-Barroso, A. Vazdekis (4) J.
Falcón-Barroso, K. Fathi, E. Emsellem, M. Bureau,
H. Kuntschner, R.L. Davies rest of the SAURON
team.
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1. What do simple colour maps show?

• A sample of highly inclined (igt50º) nearby
  galaxies to look at pure bulges with no disk
  contamination.
• Photometry of 45 nearby bulges
• (Balcells Peletier 1994)
• (Andredakis et al. 1995)
• (Peletier Balcells 1997)
• (Balcells et al. 2003, 2004a,b)
• Kinematics of 20 nearby bulges
• (Falcón-Barroso et al. 2003b)
• Stellar Populations of 20 bulges
• (Peletier et al. 1999)
• (Falcón-Barroso et al. 2002)
• (Falcón-Barroso et al. 2003a)

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Can we see the peanut-shaped bulge in the color
maps?
NGC 5965 a galaxy with a peanut-shaped bulge
(Sb)
R-K colour map (Peletier Balcells 1997)
U-R colour map (Peletier Balcells 1997)
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What do optical-infrared colours tell us?
NGC 5838 B-I (field size 5''x5'')
HST colour-colour maps of 20 S0-Sbc bulges Red
Central values Blue Values at 0.5 Re. gt
Centers are dusty, and so contain young st.
Populations (Peletier et al. 1999)
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• From the optical-infrared colour maps we infer
• These early-type bulges are predominantly old
  (10 Gyr) with relatively small scatter (2 Gyr)
• Bulge and inner disk populations are very similar
  (Peletier Balcells 1996, Terndrup et al. 1994)
• One does not see the bulge (classical nor peanut)
  in the colour maps, indicating also that there
  are no shocks etc. in the corners of the peanut
  that cause star formation.
• There is residual dust and star formation in the
  centers

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2. Do stellar populations of bulges vary from
those of ellipticals? The case of the Ca triplet.
(Cenarro et al. 2001, 2002ab, Vazdekis et al.
2003, Saglia et al. 2002, Falcon-Barroso et al.
2003, Cenarro et al. 2003)
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New near-IR index definitions CaT, CaT,PaT

• Advantages
• Specifically designed to ease problems in the
  definition of the continuum bands
• Use all the S/N in the Ca triplet lines
• Are not very sensitive to problems with sky
  subtraction (5 continuum bands).
• Correct for Pa line contribution
• Calibrated with the stellar library of Cenarro
  et al.

(Cenarro et al. 2001a, 2001b, 2002)
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Discovery of a CaT - s relation for bulges
(Falcon-Barroso et al. 2003)

• Ca II anti-correlates with ?
• No dependence on aperture size or morphological
  type.

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The CaT - s relation is the same for bulges as
for ellipticals.

• Bulges of Spiral galaxies (filled symbols) follow
  the relation defined by elliptical galaxies
  (from Cenarro et al. 2003, open circles).

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How do we explain that CaT decreases for larger
galaxies?
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For metallicities gt -0.5 CaT is virtually
independent of metallicity.
GLOBULAR CLUSTERS
Model prediction estimates
Metallicity scale of Armandroff Zinn (1988)
M/H
Vazdekis et al. (2003)
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M/H
But CaT does depend on IMF-slope!
A G E
IMF slope
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The CaT measurements in bulges can be explained

• If Ca/Fe lt 0
• If Ca is depleted onto grains. This is not very
  likely, since the CaT - s relation for
  ellipticals (with less dust) is the same as for
  bulges.
• If the largest galaxies have IMFs that are biased
  towards low mass stars.

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3. Where do bulges fall on the Fundamental Plane
of early-type galaxies? (Falcon-Barroso et al.
2002)
(B92 Bender et al 1992, J96 JØrgensen et al.
1996)
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Bulges on the Fundamental Plane in the K-band
(P98 Pahre et al. 1998)
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The position of bulges on the FP shows that these
early-type bulges have the same age on the
average as elliptical galaxies in clusters.
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What does the Mg2 s relation say about the ages
of these bulges?
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According to the Mg2-s relation these bulges are
old. However, there are other bulges that are
apparently younger (e.g. most of those of
Prugniel et al. 2001).
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4. Absorption line strength maps of Early-type
bulges with SAURON
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The SAURON Sample 24 Es, 24 S0s, 24 Sas.

• E
• S0
• Sa

The SAURON sample is a representative sample of
optically selected ellipticals, S0s and
spirals. Here I will show some absorption line
strength maps for the 24 Sa galaxies.
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Separating gas and stars
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The system of line indices (Lick)
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Some characteristic cases
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Central Star Formation
(SB(r)a )
I
Mgb
Hß
Vstars
Vgas
Fe 5015
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Stellar Populations Ignoring the Bar
(SB(s)0-)
I
Mgb
Hß
Vgas
Vstars
Fe 5015
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A Central Star Formation Ring
(SB(rs)a)
Mgb
Hß
I
Vgas
Vstars
Fe 5015
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What can we say about secular evolution from
stellar populations?
Bulges of early-type spirals (S0-Sb) look almost
like elliptical galaxies

• Similarities
• B-I I-H colours similar to ellipticals of the
  same size. Old ages.
• Bulges on the FP of ellipticals.
• Same Mg2-s and CaT-s relation
• No features in colour maps
• Some central (SF) activity

• Differences
• Sérsic index n lower (1-2.5 vs. 4)

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• BUT!
• Bulges and inner disks are indistinguishable in
  the colour maps

• Bulges of later types are different
• Star clusters (nuclear and non-nuclear)
• Presence of Star Formation (in Rings etc.)
• Surface brightness profiles even shallower (n1)

Clearly, later type bulges are evolving as we
speak. About the details, however, we know very
little.
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First Light of VISIR

• VISIR is a mid-infrared imager and spectrograph,
  built by CEA-Saclay (France) and ASTRON
  (Dwingeloo) for ESOs VLT. It has the following
  capabilities
• Diffraction limited imaging from 5-28 micron
  (0.2 at 8 micron!)
• Spectroscopy at resolution 300, 3000 and 30000.
• VISIR obtained first light on April 30, 2004.

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Some Early VISIR-Results
Galactic center at 8.6 (PAH), 12.8 (NeII) and
19.5 micron.
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The Ant Nebula
HST
VISIR 12.8 micron, Field of View 33x33
VISIR NeII line at 12.8 micron, x-v diagram
scale 33 x 700 km/s