shapley scs lec1

Galaxy Formation and Evolution (in Clusters) #1: 

Galaxy Formation and Evolution (in Clusters) #1 Alice Shapley (Princeton) June 14, 15, 16th, 2006

Overview and Motivation: 

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

0. Introductory Remarks about Galaxy Formation and Evolution : 

0. Introductory Remarks about Galaxy Formation and Evolution

Different Types of Galaxies: 

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)

History of Galaxy Evolution : 

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

History of Galaxy Evolution : 

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 Don’t use elliptical galaxies to measure cosmic deceleration!!!!

Models of Galaxy Evolution : 

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

Models of Galaxy Evolution : 

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

Models of Galaxy Evolution : 

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

Monolithic Collapse: 

Monolithic Collapse Eggen, Lynden-Bell andamp; 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)

Monolithic Collapse: 

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

Hierarchical Stucture Formation: 

Hierarchical Stucture Formation Whereas monolithic collapse works backwards from present using understanding of stellar evolution and stellar dynamics (what’s 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)

Hierarchical Stucture Formation: 

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: what’s the best way to constrain the baryonic physics of galaxy formation, now that there appears to be agreement on underlying cosmological model?

Hierarchical Stucture Formation: A comment on the meaning of “formation”: 

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

Why Clusters are Useful: 

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 z=1.45 (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

I. Galaxy Evolution in Clusters from z~0-1: 

I. Galaxy Evolution in Clusters from z~0-1

Evolution of E/S0 galaxies : 

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 zandgt;2 (evidence for passive evolution? monolithic collapse?)  Evolution of colors  Evolution of Color-Magnitude (CM) relation  M/LB from evolution in Fundamental Plane

Evolution of E/S0 galaxies : 

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 zandgt;2 (Bower et al. 1992)

Evolution of E/S0 galaxies : 

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 zandgt;2 (Bower et al. 1998)

Evolution of E/S0 galaxies : 

Evolution of E/S0 galaxies Early-type galaxies in local clusters form a homogeneous class z~0 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)

Evolution of E/S0 galaxies : 

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 z~0.5 (use HST for morphological separation) CM-relation has same slope at z~0.5 as z~0, small scatter, which does not increase at fainter magnitudes Tight scatter at z~0.5 can be understood if bulk of sf occurred 5-6 Gyr ago zandgt;2 z=0.56 Central ~1 Mpc

Evolution of E/S0 galaxies : 

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 z~0.5 (use HST for morphological separation) CM-relation has same slope at z~0.5 as z~0, small scatter, which does not increase at fainter magnitudes Tight scatter at z~0.5 can be understood if bulk of sf occurred 5-6 Gyr ago zandgt;2 (images are 10'x10' or 60x60 kpc)

Evolution of E/S0 galaxies : 

Evolution of E/S0 galaxies Evolution in E/S0 colors vs. z can give us some clues about early-type galaxy formation z=0.56 Ellis et al. (1997) look at CM relation in clusters at z~0.5 (use HST for morphological separation) CM-relation has same slope at z~0.5 as z~0, small scatter, which does not increase at fainter magnitudes Tight scatter at z~0.5 can be understood if bulk of sf occurred 5-6 Gyr ago zandgt;2 Coma CMD w/0 color evolution

Evolution of E/S0 galaxies : 

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 0.3andlt;zandlt;0.9, (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

Evolution of E/S0 galaxies : 

Evolution of E/S0 galaxies Evolution in E/S0 M/LBvs. z can give us some clues about early-type galaxy formation Offset in FP 0-pt indicates difference in M/LB (see problem) From Treu et al. (2005)

Evolution of E/S0 galaxies : 

Evolution of E/S0 galaxies Evolution in E/S0 M/LBvs. z can give us some clues about early-type galaxy formation van Dokkum andamp; Stanford (2003) look at cluster at z=1.27, 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 z~2 Statistics at z~1 not great!

Evolution of E/S0 galaxies : 

Evolution of E/S0 galaxies Some unresolved questions at z~1: De Lucia et al. (2004) construct CM relations for 4 z~0.7-0.8 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 z=0.83 and find no deficit Interloper corrections!

Evolution of E/S0 galaxies : 

Evolution of E/S0 galaxies Some unresolved questions at z~1: De Lucia et al. (2004) construct CM relations for 4 z~0.7-0.8 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 z=0.83 and find no deficit Interloper corrections!

Evolution of E/S0 galaxies : 

Evolution of E/S0 galaxies Some unresolved questions at z~1: Homeier et al. (2006) measure CM-relation in clusters at z~0.9 (part of supercluster), and find evidence for scatter increasing at fainter magnitudes, consistent with younger ages

Evolution of E/S0 galaxies : 

Evolution of E/S0 galaxies Some unresolved questions at z~1: 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 z~0.3-1.2 Note: evidence at z~0.4 that field E/S0 are younger by 20% than cluster E/S0, zformandgt;1.5 (van Dokkum et al. 2001)

Evolution of Galaxy Mix : 

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/E+A)

To be continued….: 

To be continued….