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Disentangling Luminosity, Morphology, Stellar Age, Star Formation, and Environment in Galaxy Evolution
Daniel Christlein Andes Fellow
Yale University & Universidad de Chile &
Ann Zabludoff (U Arizona)
?=
Kant: Systems of Fixed Stars, Arrangements of Worlds, Worlds of Worlds, Milky Ways of Worlds
Island Universes
We know some basic statistics about galaxies:
- Luminosity Function
- Morphology-Environment Relation
- Star Formation-Environment Relation
but understanding incomplete:
-environmental dependence of LF?
-origin of morphological sequence?
-Nature or Nurture?
< Binggeli, Sandage & Tamman 1988
The Data
- 6 nearby (z<0.07), rich clusters
- R-band photometry
- spectroscopy for ~3000 galaxies:
star formation indices, stellar age indices
- 2MASS J-, K-photometry -> stellar mass
- quantitative morphology with GIM2D (Simard 2002)
- new ML algorithm
Abell 1060
Christlein & Zabludoff (2003)
Is Luminosity Function Dependent on Environment?
● field and cluster overall GLFs same
● no difference for star-forming galaxies
● GLFs for quiescent galaxies steeper in clusters
X
● steepening of quiescent LF ●difference between field and groups, not groups and clusters
Which Environments Shape the GLF?
Which Environments Shape the GLF?
GLFs are pretty uniform in clusters (>60%, >40% for NEL)
all galaxies quiescent galaxies
- the high-mass end
● quiescent GLF● dwarf/giant ratio● uniformity of GLF in clusters● 2dF & SDSS: break in SFR●
cD < 400 km s-1
● gE in subclumps ● early type fraction ● HI deficiency in groups
many saturation points:
=> Groups are where it's at! Gomez et al.
Lewis et al.
Are Groups the Most Important Environments?
x
● quantify morphology by bulge fraction (B/T; GIM2D)
● dense environments => higher bulge fraction
● two types of transformation mechanisms:
● disk fading (e.g., ram-pressure stripping, strangulation)● increasing bulge luminosity (e.g., tidal interactions, mergers)
Christlein & Zabludoff 2004
How to Make an Early-Type Galaxy
The Discrete Maximum Likelihood Method
- ansatz for parent distribution:
- pipe it through maximum likelihood optimizer
- natural treatment of multivariate distributions- correct relative normalization- easy to code- retains advantage of ML method
Christlein, McIntosh & Zabludoff, 2004
X
How to Make an Early-Type Galaxy
B/T
0.7 1.0E
disk-dominated
bulges are brighter, but disks not fainter, in bulge-dominated systems
=> bulge-dominated systems (e.g., "S0s") cannot be producedby disk-fading alone
Star Formation
Morphology
Stellar Mass
Stellar Age
Star formation gradient and morphology-environment relation the same?
Star formation gradient due to initial conditions?
Partial Correlation Coefficients
rStar Formation,Environment . Morphology,Stellar Mass, Mean Stellar Age
Star Formation EW([OII])
Environment R
Morphology B/T
Stellar Mass from 2MASS J, K & D4000
Mean Stellar Age D4000
hold constantresidual correlation
Removing Morphology, Stellar Mass, Stellar Age...
total SF gradient residual SF gradient
r = 0.295 (Z=10.9) r = 0.221 (Z=8.0)
=> SF gradient not explained by Morphology, Stellar Mass, Stellar Age gradients
Conclusions
LF vs. environment - little change in LF from field -> cluster or cluster -> cluster
- significant steepening of quiescent LF field -> groups
- little variation of quiescent LF groups -> clusters or cluster -> cluster
=> strong impact of environment on SF properties, little on luminosity
=> lower-density envs. decisive
Bulge/Disk LFs vs. Morph. & Env.
-Early Types are Early Types because
Bulges are brighter, not because Disks are
fainter
=> Bulge-enhancing processes (e.g., tidal interactions, mergers) necessary -> low-density envs
Conclusions(2)
Residual SF gradient remains after accounting for Morphology, Stellar Mass, Stellar Age
- smoking gun for late-epoch environmental transformations
- net effect of evolutionary/formation mechanisms on star formation & morph. dependent on environment
Conclusions (3)
- Which Environment?
Radius or Local Density?
Morph. Evolution (bulge enhancement) probably driven by LD
but residual SF impact could have different dependence
- define environmental indices sensitive to mechanisms?
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