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 0.2late-type spirals

How to Make an Early-Type Galaxy

B/T

0.2 0.3early-type spirals

How to Make an Early-Type Galaxy

B/T

0.3 0.4early-type spirals & S0s

How to Make an Early-Type Galaxy

B/T

0.4 0.5S0

How to Make an Early-Type Galaxy

B/T

0.5 0.7S0s & Es

How to Make an Early-Type Galaxy

B/T

0.7 1.0E

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

The Star Formation Gradient

Gomez et al.

Lewis et al.

Christlein & Zabludoff 2004bMorDen

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)

The End

Morphology-Environment Relation

SF gradientThe End

- 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?

uncorrected

corrected

Corrected vs. uncorrected Spearman Coefficients

The End

Corrected vs. uncorrected Spearman Coefficients

<r>=0

uncorrected rcorrected r

The End