Image Decomposition of Barred Galaxies

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Image Decomposition of Barred Galaxies and AGN
Hosts Dimitri Gadotti Max Planck
Institute for Astrophysics
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Outline

• Tests and exercises on the reliability of image
  decomposition
• brief introduction and results for a very nearby
  sample (z 0.005)
• the effects of not including bars
• the effects of not accounting for bright, type 1
  AGN
• artificially redshifted images
• the effects of low physical spatial resolution
• some consequences
• the stellar mass budget in the local universe

Dimitri Gadotti (MPA) Image Decomposition of
Barred Galaxies and AGN Hosts
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The BUDDA Code (de Souza, Gadotti dos Anjos
2004)

• BUlge/Disk Decomposition Analysis v2.1 (Gadotti
  2008)
• (http//www.mpa-garching.mpg.de/dimitri/budda.htm
  l)
• 2D (Image Fitting)
• Bulge (Sérsic 1968)
• Disk (Freeman 1970)

Dimitri Gadotti (MPA) Image Decomposition of
Barred Galaxies and AGN Hosts
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The BUDDA Code (de Souza, Gadotti dos Anjos
2004)

• BUlge/Disk Decomposition Analysis v2.1 (Gadotti
  2008)
• (http//www.mpa-garching.mpg.de/dimitri/budda.htm
  l)
• 2D (Image Fitting)
• Bar
• Sérsic profile
• n1 late-type bars
• nlt1 early-type bars

Dimitri Gadotti (MPA) Image Decomposition of
Barred Galaxies and AGN Hosts
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The BUDDA Code (de Souza, Gadotti dos Anjos
2004)

• BUlge/Disk Decomposition Analysis v2.1 (Gadotti
  2008)
• (http//www.mpa-garching.mpg.de/dimitri/budda.htm
  l)
• 2D (Image Fitting)
• Central Source
• Moffat (1969)

Dimitri Gadotti (MPA) Image Decomposition of
Barred Galaxies and AGN Hosts
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BUDDA on Very Nearby Galaxies 17 galaxies
(mostly barred and some AGN) _at_ V R
broadbands resolution 150 pc Gadotti de Souza
(2006)
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Athanassoula (1992a, b)
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Athanassoula (1992a, b)
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BUDDA on Very Nearby Galaxies
Kormendy (1977) relation for bulges
scaling relation for disks
Dimitri Gadotti (MPA) Image Decomposition of
Barred Galaxies and AGN Hosts
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BUDDA on Very Nearby Galaxies

• bar ellipticity from image fitting

1 b/a

• effect is on average 20, but a factor of 3 is
  also seen

ellipticity peak in ellipse fitting
bars might be more eccentric!
Dimitri Gadotti (MPA) Image Decomposition of
Barred Galaxies and AGN Hosts
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BUDDA on Very Nearby Galaxies
What if you dont include bars?
Dimitri Gadotti (MPA) Image Decomposition of
Barred Galaxies and AGN Hosts
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BUDDA on Very Nearby Galaxies
What if you dont include bars?
D/T increase by 10 (average) 30 maximum
B/T increase by 50 (average) 100 maximum See
also Laurikainen, Salo Buta (2005)
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BUDDA on Very Nearby Galaxies
What if you dont include AGN?
Dimitri Gadotti (MPA) Image Decomposition of
Barred Galaxies and AGN Hosts
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BUDDA on Artificially Redshifted
Galaxies resolution 1.5 kpc
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BUDDA on Artificially Redshifted Galaxies
What if you go for farther galaxies?
original images
resolution 1.5 kpc 1.5 _at_ z 0.05 (my SDSS
sample) 0.75 _at_ z 0.1 (MGC Allen et al.
2006) HST, VLT (w/ AO) _at_ z 1-2
artificially redshifted images
Dimitri Gadotti (MPA) Image Decomposition of
Barred Galaxies and AGN Hosts
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• general good agreement
• disk parameters are the most robust
• B/T overestimated on average by 5 (re seeing
  radius)

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BUDDA on Artificially Redshifted Galaxies
What if you go for farther galaxies?

• bar effect still present (even worse for re)
• AGN light is diluted

Dimitri Gadotti (MPA) Image Decomposition of
Barred Galaxies and AGN Hosts
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The Stellar Mass Budget at z 0

• Driver et al. (2007)
• 26/-4 (bulges)
• 58/-6 (disks)
• Correcting for
• 5 overestimation of B/T due to poor resolution
• average overestimation of (models without bars)
• B/T (50)
• D/T (10)
• bar fraction of 70
• Results in
• 13.5 (bulges), 58.5 (disks), 12 (bars)

Dimitri Gadotti (MPA) Image Decomposition of
Barred Galaxies and AGN Hosts
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The Stellar Mass Budget at z 0

• Bars as important as spheroids in the stellar
  mass budget at z 0 (Gadotti 2008)

• 1/2 in disks

• 15 in bars

• 15 in elliptical galaxies

• 15 in bulges

Dimitri Gadotti (MPA) Image Decomposition of
Barred Galaxies and AGN Hosts
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Summary

• Structural analysis of high spatial resolution
  images must take into account bars and type 1 AGN
  (otherwise B/T is overestimated ? wrong
  comparison to models)
• At lower spatial resolution AGN light is diluted
  but bars remain important
• Image decomposition works fine for SDSS at z
  0.05, but B/T is overestimated by 5 on average
  if re seeing
• True axial ratio of bars can only be obtained
  through image decomposition (ellipse fits result
  in rounder bars if axisymmetric component is
  strong)
• Bars as important as spheroids in the stellar
  mass budget at z 0

Dimitri Gadotti (MPA) Image Decomposition of
Barred Galaxies and AGN Hosts
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The BUDDA Code (de Souza, Gadotti dos Anjos
2004)
generalized ellipses (e.g., Athanassoula et al.
1990)
Pure c 2
Boxy c gt 2
Disky c lt 2
Dimitri Gadotti (MPA) Image Decomposition of
Barred Galaxies and AGN Hosts
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BUDDA on Very Nearby Galaxies
bar semi-major axis from image fitting
scale-length of disk (see also Erwin 2005)
bar semi-major axis from ellipse fitting
Dimitri Gadotti (MPA) Image Decomposition of
Barred Galaxies and AGN Hosts
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BUDDA on Very Nearby Galaxies
comparison with Laurikainen et al. (2004) and
Laurikainen, Salo Buta (2005)
Dimitri Gadotti (MPA) Image Decomposition of
Barred Galaxies and AGN Hosts
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BUDDA on Very Nearby Galaxies Two special cases
Gadotti de Souza (2003) where is the disk?
(fits without bar) Rearrangement (capture) of
disk stars by evolving bar (Athanassoula
Misiriotis 2002 Athanassoula 2003)
Dimitri Gadotti (MPA) Image Decomposition of
Barred Galaxies and AGN Hosts
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BUDDA on Very Nearby Galaxies Two special cases
But best fit is achieved with Freeman (1970) type
II disk
Gadotti (2008) bar growth is 70, through
capture of 13 of disk stars (one and only
observational constraint to date)
Dimitri Gadotti (MPA) Image Decomposition of
Barred Galaxies and AGN Hosts