Galaxy Formation and Evolution in Clusters

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Galaxy Formation and Evolution (in Clusters) 1

• Alice Shapley (Princeton)
• June 14, 15, 16th, 2006

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Overview and Motivation

• 0. Introductory remarks about galaxy
  formation evolution and why clusters are useful
  for this
• Galaxy evolution in clusters from z0-1
  (emphasis on early-type)
• Galaxy evolution in general from z0-1
• Direct observations of cluster galaxy
  progenitors forming at high redshift (z 2)
• Protoclusters at high redshift (z 2)

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0. Introductory Remarks about Galaxy Formation
and Evolution
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Different Types of Galaxies

• Galaxies observed in different forms
• Divide by morphology, color, spectra
• E.g., morphological type E/S0 vs. spiral
• 80 of galaxies in cores of nearby clusters are
  E/S0 (Dressler 1980)
• Galaxies of different types have different
  formation mechanisms

Strateva et al. (2001)
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History of Galaxy Evolution

• Traditionally, galaxies used to constrain
  cosmological model (Sandage 1961)
• Cosmological tests compare measure of distance
  and redshift e.g., apparent magnitude, m, of
  standard candle (with known M) vs. redshift

Initially used cluster elliptical galaxies as
standard candles
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History of Galaxy Evolution

• Not only were galaxies brighter in the past
  (i.e., at higher z, M was brighter), but, Tinsley
  (1976) pointed out uncertainties in dM/dt
  translate into unacceptable uncertainties in q0
  (form of IMF, metallicity, star-formation
  history)
• In order to constrain q0, need to know
  evolutionary correction to high precision

Dont use elliptical galaxies to measure cosmic
deceleration!!!!
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Models of Galaxy Evolution
Of course, there is mutual uncertainty
uncertainty in evolution of galaxies hinders
interpretation of cosmological tests BUT
uncertainty in cosmological model hinders
interpretation of galaxy evolution data
Population synthesis models tell how SED evolves
with TIME -- but we observe galaxy mags, colors,
spectra at different REDSHIFTS Growth of
structure (e.g., the halo mass function and its
evolution) depends on cosmological parameters
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Models of Galaxy Evolution
Of course, there is mutual uncertainty
uncertainty in evolution of galaxies hinders
interpretation of cosmological tests BUT
uncertainty in cosmological model hinders
interpretation of galaxy evolution data
Population synthesis models tell how SED evolves
with TIME -- but we observe galaxy mags, colors,
spectra at different REDSHIFTS Growth of
structure (e.g., the halo mass function and its
evolution) depends on cosmological parameters
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Models of Galaxy Evolution

• Late 1970s, motivation for studying distant
  galaxies became not only for cosmological probes,
  but rather for understanding their history and
  formation
• Two basic paradigms for understanding galaxy
  formation
• ? Monolithic collapse
• ? Hierarchical structure formation

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Monolithic Collapse

• Eggen, Lynden-Bell Sandage (1962) observed
  that metal-poor halo stars in the Milky Way have
  highly elliptical orbits characteristic of system
  in free-fall
• Metal-rich stores have more disk-like
  distribution and kinematics

Color (bluer, metal poorer)
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Monolithic Collapse

• Interpretation 1010 years ago protogalaxy
  collapsed from intergalactic material, collapse
  was rapid (108 years for equilibrium to be
  reached), big burst of star-formation, formed
  stars with eccentric orbits during collapse, disk
  stars formed later

Color (bluer, metal poorer)
Monolithic collapse classical formation
mechanism for ellipticals and bulges, which are
collections of old stars
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Hierarchical Stucture Formation

• Whereas monolithic collapse works backwards from
  present using understanding of stellar evolution
  and stellar dynamics (whats the cosmological
  model?), hierarchical structure formation works
  from within the ?CDM cosmological framework,
  provides ab initio model for galaxy formation,
  motivated by CMB and large-scale structure
• Galaxy formation and evolution is a natural
  consequence of the growth of the power spectrum
  of fluctuations by gravitational instability, in
  a universe dominated by dark matter
• Model predicts evolution of dark matter halo
  mass function through merging and accretion

(Springel et al. 2005)
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Hierarchical Stucture Formation

• While the evolution of the dark matter is now
  fairly well understood (gravity, cosmological
  model), tracing the evolution of the baryons is
  complicated!
• Gas cooling and other hydrodynamical effects,
  star formation and IMF, feedback (from AGN and
  supernovae)
• Unfortunately, it is all these messy baryonic
  processes that translate the population of dark
  matter halos into the galaxies that we observe
  over a range of cosmic epochs.
• Big question whats the best way to constrain
  the baryonic physics of galaxy formation, now
  that there appears to be agreement on underlying
  cosmological model?

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Hierarchical Stucture Formation A comment on the
meaning of formation

• Possible difference between redshift at which
  XX of stars formed vs. redshift at which XX of
  stars were assembled into one unit

From de Lucia et al. (2005), on formation of
elliptical galaxies Semi-analytic model (w/AGN
feedback) grafted onto Millennium DM Simultion
Star-formation
Mass Assembly
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Why Clusters are Useful

• Clusters useful for galaxy evolution studies
  because (based on various identification
  techniques X-ray, optical/red-sequence, lensing,
  SZ) a cluster provides a large samples of
  galaxies at the same redshift and relatively
  compact field, now to z1.45 (Stanford et al.
  2006)
• Also, close proximity of galaxies with each
  other and ICM allows for study of environmental
  effects in high density environments
  (gravitational and hydrodynamical)
• Complexities to join in timeline, need to
  understand how clusters at high redshift relate
  to clusters at lower redshift (e.g., in terms of
  mass) -- also need to understand variation in
  cluster populations at each redshift before
  connecting cluster galaxies at different redshifts

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I. Galaxy Evolution in Clusters from z0-1
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Evolution of E/S0 galaxies

• Collectively refer to E/S0 as early-type
  galaxies (may be some ambiguity in classifying
  each type), the type that make up 80 of galaxy
  population in cores of nearby clusters. HST
  important for morph. Classification at higher
  redshift.
• Evidence that stars in these galaxies formed at
  zgt2 (evidence for passive evolution? monolithic
  collapse?)
• ? Evolution of colors
• ? Evolution of Color-Magnitude (CM) relation
• ? ?M/LB from evolution in Fundamental Plane

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Evolution of E/S0 galaxies

• Early-type galaxies in local clusters form a
  homogeneous class

• Color-magnitude diagram in Virgo/Coma scatter
  is 0.05 mag, of which 0.03 mag is observational
  error
• Physical sequence is increasing metallicity at
  increasing mass
• Small scatter around relation implies that stars
  (galaxies) formed at zgt2
• (Bower et al. 1992)

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Evolution of E/S0 galaxies

• Early-type galaxies in local clusters form a
  homogeneous class

• Color-magnitude diagram in Virgo/Coma scatter
  is 0.05 mag, of which 0.03 mag is observational
  error
• Physical sequence is increasing metallicity at
  increasing mass
• Small scatter around relation implies that stars
  (galaxies) formed at zgt2
• (Bower et al. 1998)

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Evolution of E/S0 galaxies

• Early-type galaxies in local clusters form a
  homogeneous class

• z0 Fundamental Plane
• Relationship among velocity dispersion, surface
  brightness, and effective radius
• Implies M/L?M0.24 with small scatter (20),
  which also implies small age scatter at fixed mass

(Jorgensen et al. 1996)
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Evolution of E/S0 galaxies

• Evolution in E/S0 colors vs. z can give us some
  clues about early-type galaxy formation

• Ellis et al. (1997) look at CM relation in
  clusters at z0.5 (use HST for morphological
  separation)
• CM-relation has same slope at z0.5 as z0, small
  scatter, which does not increase at fainter
  magnitudes
• Tight scatter at z0.5 can be understood if bulk
  of sf occurred 5-6 Gyr ago zgt2

Central 1 Mpc
z0.56
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Evolution of E/S0 galaxies

• Evolution in E/S0 colors vs. z can give us some
  clues about early-type galaxy formation

• Ellis et al. (1997) look at CM relation in
  clusters at z0.5 (use HST for morphological
  separation)
• CM-relation has same slope at z0.5 as z0, small
  scatter, which does not increase at fainter
  magnitudes
• Tight scatter at z0.5 can be understood if bulk
  of sf occurred 5-6 Gyr ago zgt2

(images are 10x10 or 60x60 kpc)
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Evolution of E/S0 galaxies

• Evolution in E/S0 colors vs. z can give us some
  clues about early-type galaxy formation

Coma CMD w/0 color evolution

• Ellis et al. (1997) look at CM relation in
  clusters at z0.5 (use HST for morphological
  separation)
• CM-relation has same slope at z0.5 as z0, small
  scatter, which does not increase at fainter
  magnitudes
• Tight scatter at z0.5 can be understood if bulk
  of sf occurred 5-6 Gyr ago zgt2

z0.56
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Evolution of E/S0 galaxies

• Evolution in E/S0 colors vs. z can give us some
  clues about early-type galaxy formation

• Stanford et al. (1998) look at clusters at
  0.3ltzlt0.9, (again use HST for morph.
• Colors get bluer consistent w/ expectations from
  passive evolution, roughly independent of cluster
  props., CMD slope does not evolve (CMD is M-Z),
  nor does scatter
• Again, consistent with stars being formed in
  single episode at high redshift, relative age
  spread low

slope
scatter
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Evolution of E/S0 galaxies

• Evolution in E/S0 M/LBvs. z can give us some
  clues about early-type galaxy formation

From Treu et al. (2005)

• Offset in FP 0-pt indicates difference in M/LB
  (see problem)

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Evolution of E/S0 galaxies

• Evolution in E/S0 M/LBvs. z can give us some
  clues about early-type galaxy formation

Statistics at z1 not great!

• van Dokkum Stanford (2003) look at cluster at
  z1.27, spectra for 3 galaxies, see how they
  relate to local fundamental plane. Offset in FP
  0-pt indicates difference in M/LB
• Mean star-formation age higher than z2

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Evolution of E/S0 galaxies

• Some unresolved questions at z1

• De Lucia et al. (2004) construct CM relations for
  4 z0.7-0.8 EDisCS clusters, find deficit of
  faint red galaxies, relative to Coma, important
  implications for formation of fainter red
  galaxies
• BUT Andreon et al. (2005) analyze MS 1054-083 at
  z0.83 and find no deficit
• Interloper corrections!

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Evolution of E/S0 galaxies

• Some unresolved questions at z1

• De Lucia et al. (2004) construct CM relations for
  4 z0.7-0.8 EDisCS clusters, find deficit of
  faint red galaxies, relative to Coma, important
  implications for formation of fainter red
  galaxies
• BUT Andreon et al. (2005) analyze MS 1054-083 at
  z0.83 and find no deficit
• Interloper corrections!

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Evolution of E/S0 galaxies

• Some unresolved questions at z1

• Homeier et al. (2006) measure CM-relation in
  clusters at z0.9 (part of supercluster), and
  find evidence for scatter increasing at fainter
  magnitudes, consistent with younger ages

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Evolution of E/S0 galaxies

• Some unresolved questions at z1

• What about field E/S0 galaxies? Treu et al.
  (2005) find difference in M/LB evolution stronger
  for less massive morphologically-selected E/S0
  galaxies over redshift range z0.3-1.2
• Note evidence at z0.4 that field E/S0 are
  younger by 20 than cluster E/S0, zformgt1.5 (van
  Dokkum et al. 2001)

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Evolution of Galaxy Mix

• While cluster E/S0 appear homogeneous, with
  stars formed at high redshift and passively
  evolving, there is evidence that cluster galaxy
  population mix is evolving
• Multiple ways to consider this, historically,
  which are all correlated
• Evolution in morphological mix (morph-dens
  relation)
• Evolution in mix of red/blue galaxies
  (Butcher/Oemler)
• Evolution in spectral types of galaxies
  (em/abs/EA)

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To be continued.