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Disentangling Luminosity, Morphology, Stellar Age, Star Formation, and Environment in Galaxy Evolution

Kant : Systems of Fixed Stars, Arrangements of Worlds, Worlds of Worlds, Milky Ways of Worlds. Island Universes. Disentangling Luminosity, Morphology, Stellar Age, Star Formation, and Environment in Galaxy Evolution. Daniel Christlein Andes Fellow Yale University & Universidad de Chile &

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Disentangling Luminosity, Morphology, Stellar Age, Star Formation, and Environment in Galaxy Evolution

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  1. Kant: Systems of Fixed Stars, Arrangements of Worlds, Worlds of Worlds, Milky Ways of Worlds Island Universes 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) ? =

  2. We know some basic statistics about galaxies: - Luminosity Function - Morphology-Environment Relation - Star Formation-Environment Relation < Binggeli, Sandage & Tamman 1988 but understanding incomplete: -environmental dependence of LF? -origin of morphological sequence? -Nature or Nurture?

  3. 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

  4. Is Luminosity Function Dependent on Environment? Christlein & Zabludoff (2003) • field and cluster overall GLFs same • no difference for star-forming galaxies • GLFs for quiescent galaxies steeper in clusters X

  5. Which Environments Shape the GLF? • steepening of quiescent LF • difference between field and groups, not groups and clusters

  6. Which Environments Shape the GLF? - the high-mass end all galaxies quiescent galaxies GLFs are pretty uniform in clusters (>60%, >40% for NEL)

  7. Are Groups the Most Important Environments? x Lewis et al. many saturation points: • 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 Gomez et al. => Groups are where it's at!

  8. How to Make an Early-Type Galaxy Christlein & Zabludoff 2004 • 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)

  9. The Discrete Maximum Likelihood Method Christlein, McIntosh & Zabludoff, 2004 - 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 X

  10. How to Make an Early-Type Galaxy B/T  0 0.2 late-type spirals

  11. How to Make an Early-Type Galaxy B/T  0.2 0.3 early-type spirals

  12. How to Make an Early-Type Galaxy B/T  0.3 0.4 early-type spirals & S0s

  13. How to Make an Early-Type Galaxy B/T  0.4 0.5 S0

  14. How to Make an Early-Type Galaxy B/T  0.5 0.7 S0s & Es

  15. How to Make an Early-Type Galaxy B/T  0.7 1.0 E

  16. How to Make an Early-Type Galaxy bulges are brighter, but disks not fainter, in bulge-dominated systems => bulge-dominated systems (e.g., "S0s") cannot be produced by disk-fading alone disk-dominated B/T  0.7 1.0 E

  17. The Star Formation Gradient Lewis et al. Gomez et al. Christlein & Zabludoff 2004b MorDen

  18. Morphology Stellar Mass Stellar Age Star formation gradient and morphology-environment relation the same? Star formation gradient due to initial conditions? Star Formation

  19. 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 residual correlation hold constant

  20. Removing Morphology, Stellar Mass, Stellar Age... residual SF gradient total 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

  21. 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

  22. Conclusions(2) 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

  23. Conclusions (3) 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

  24. The End

  25. Morphology-Environment Relation SF gradient The End

  26. - 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?

  27. Corrected vs. uncorrected Spearman Coefficients corrected uncorrected The End

  28. Corrected vs. uncorrected Spearman Coefficients <r>=0 corrected r uncorrected r The End

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