image decomposition of barred galaxies and agn hosts dimitri gadotti
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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
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