Image Decomposition of Barred Galaxiesand AGN Hosts

Dimitri GadottiMax Planck Institute for Astrophysics

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

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.html)

• 2D (Image Fitting)

• Bulge (Sérsic 1968)

• Disk (Freeman 1970)

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

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.html)

• 2D (Image Fitting)

• Bar• Sérsic profile• n=1: late-type bars• n<1: early-type bars

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

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.html)

• 2D (Image Fitting)

• Central Source• Moffat (1969)

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

BUDDA on Very Nearby Galaxies

17 galaxies (mostly barred and some AGN) @ V & R broadbandsresolution ~ 150 pc

Gadotti & de Souza (2006)

Athanassoula (1992a, b)

Athanassoula (1992a, b)

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

BUDDA on Very Nearby Galaxies

ellipticity peak in ellipse fitting

1 – b/a

bars might be more eccentric!

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

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

• bar ellipticity from image fitting

BUDDA on Very Nearby Galaxies

What if you don’t include bars?

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

BUDDA on Very Nearby Galaxies

What if you don’t include bars?

D/T increase by 10% (average)30% maximum

B/T increase by 50% (average)100% maximum

See also Laurikainen, Salo & Buta (2005)

BUDDA on Very Nearby Galaxies

What if you don’t include AGN?

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

BUDDA on Artificially Redshifted Galaxies

resolution ~ 1.5 kpc

BUDDA on Artificially Redshifted Galaxies

What if you go for farther galaxies?

original images

artificially redshifted imagesresolution = 1.5 kpc

1.5” @ z = 0.05 (my SDSS sample)0.75” @ z = 0.1 (MGC – Allen et al. 2006)

HST, VLT (w/ AO) @ z ≈ 1-2

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

• general good agreement

• disk parameters are the most robust

• B/T overestimated on average by 5% (re ~ seeing radius…)

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

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

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

• ~ 15% in bulges

• ~ 15% in bars • ~ 15% in elliptical galaxies

• ~ 1/2 in disks

The Stellar Mass Budget at z ~ 0

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

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

Purec = 2

Boxyc > 2

Diskyc < 2

generalized ellipses(e.g., Athanassoula et al. 1990)

The BUDDA Code(de Souza, Gadotti & dos Anjos 2004)

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

BUDDA on Very Nearby Galaxies

scale-length of disk (see also Erwin 2005)

bar semi-major axis from ellipse fitting

bar semi-major axis from image fitting

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

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

BUDDA on Very Nearby GalaxiesTwo 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

BUDDA on Very Nearby GalaxiesTwo special cases

Gadotti (2008): bar growth is ~ 70%, through capture of ≈ 13% of disk stars (one and only observational constraint to date)

But best fit is achieved with Freeman (1970) type II disk

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