Conference “Summary” Alice Shapley (Princeton)

Overview Multitude of new observational, multi-wavelength results on massive galaxies from z~0 to z>5: CMR/bimodality, luminosity functions, stellar mass functions, star-formation rates, clustering, AGN, structural and dynamical properties, environmental effects. Several different types of theoretical models (Millennium+SAM, cosmological SPH, zoomed-in cosmo-SPH, QSO/gas-rich-merger, dissipationless). Many different “themes”: downsizing, quenching, merging (as relates to AGN and red galaxies), feedback.

What about MGCT? Already knew about evolution of stellar mass density of red galaxies (Bell et al. 2004), but not DEEP2 or NOAO DWFS, nor explicit mass fns. Comparison of different z>1.5 survey techniques Some discussion of fact that high fraction of mass density of massive galaxies at z>1 is in star-forming galaxies, but not framed as “downsizing” (Fontana) No discussion of AGN feedback (of either kind) Less comprehensive use of Spitzer IRAC/MIPS observations as stellar mass or SF/AGN indicator

What about MGCT? Already knew about evolution of stellar mass density of red galaxies (Bell et al. 2004), but not DEEP2 or NOAO DWFS, nor explicit mass fns. Comparison of different z>1.5 survey techniques Some discussion of fact that high fraction of mass density of massive galaxies at z>1 is in star-forming galaxies, but not framed as “downsizing” (Fontana) No discussion of AGN feedback (of either kind) Less comprehensive use of Spitzer IRAC/MIPS observations as stellar mass or SF/AGN indicator

Observations up to z~1: LF Measurement of red galaxy LF out to z~1 from DEEP2, COMBO-17, NOAO DWFS, indicates growth in stellar mass density of red galaxies of factor of ~2-5 Level of agreement among surveys. Challenge of making differential measurement at low-z and z~1. Robustness of color-magnitude diagram. Do we know the evolution of this stellar mass density well enough observationally to constrain theoretical models?

Observations up to z~1: MF Differential evolution of red galaxies as a function of luminosity/mass. More massive galaxies appear to grow less between z~1 and z~0. Shown in Bundy et al. (stellar mass functions) Shown in Brown et al. (luminosity function)

Observations up to z~1: CMR vs. dynamics CMR in clusters at z~ Lack of faint red galaxies at higher redshifts (consistent with Bundy et al., or in general at z~0.8)? CMR evolution at z~ indicates z form ~3 for stars in bright red galaxies Dynamical studies (evolution of FP to z~0.5) indicate z form =2.0 for M>10 11 M sun Are these two results consistent?

Observations up to z~1: What are red z~1 galaxies? Red sequence observed in z~1 CMD. What is the nature of these red galaxies? Are they passive? Are they hosting dusty star-formation? What are their star-formation rates (AGN accretion)? To answer these questions: need multi-wavelength (Spitzer, Chandra) and spectroscopic data.

Observational constraints on models? New observations out to z~1 provide additional constraint at significant lookback time for models that try to reproduce z~0. Example: differential evolution in stellar mass function vs. stellar mass Remember: (Bundy et al)

Observational constraints on models? De Lucia et al. (Croton, White). Predict more massive z=0 ellipticals assembled later What does this model predict for the evolution of the red galaxy stellar mass function and luminosity function from z~1 to z~0?

Observational constraints on models? Additional tests: FP evolution almost indistinguishable for field and cluster galaxies (4.1% younger in field, 0.4 Gyr). Is this predicted by models? How are field and cluster defined? CMD at z~0 and z~1: are these reproduced? Ask question for both Millennium+SAM (de Lucia, White, Croton) and SPH (Davé)

Observations Beyond z~1 Arguably, z>1 is even more crucial to understand. Most of the stellar mass is already in place by z~1, and lower-z observations indicate z form ~2-3. Yan et al. 2006

Observations Beyond z~1 We heard about observations of sfr, dust extinction, AGN content, dynamics of z>1.5 galaxies. Outflows and metallicities also very important. Models of cold accretion (Davé) and merger-driven AGN activity (Hopkins) were presented. 2 observational points: AGN fraction, and nature of star formation at high redshift

Observations Beyond z~1 ~20-25% of M>10 11 M sun galaxies at z~2 may host AGN (Kriek) Few percent of UV-selected galaxies at similar redshifts host AGN (Steidel et al. 2002, 2004), typical mass fewx10 10 M sun. In UV-selected sample (Erb et al. 2006), AGN are found among most massive/oldest galaxies. Compare with Heckman result for low redshift: for emission-line AGN, as AGN lum increases, stellar pop in bulge becomes younger, dust/cold gas increases. How does z~2 narrow-line AGN phase relate to that at z~0? (progenitors of local radio AGN?) To end of star- formation episode? To M BH -  relation?

z~2 Star formation: UV-selected Well-defined sequence in [OIII]/H  vs. [NII]/H  in local galaxies (SDSS) (star- formation vs. AGN) small sample of z~2 star- forming galaxies with [OIII]/H  are offset from this locus (as is DRG) n e, ionization parameter, ionizing spectrum (IMF, star- formation history) What does this tell us about nature of SF? (Erb et al. 2006a)

z~2 Star formation: DRG Well-defined sequence in [OIII]/H  vs. [NII]/H  in local galaxies (SDSS) (star- formation vs. AGN) small sample of z~2 star- forming galaxies with [OIII]/H  are offset from this locus (as is DRG) n e, ionization parameter, ionizing spectrum (IMF, star- formation history) What does this tell us about nature of SF? (Kriek et al. 2006)

Observations Beyond z~1 What is the best way to compare between observations and simulations? Observed quantities: fluxes, colors, spectroscopic features, FP evolution, morphologies Derived quantities: star-formation rates, stellar masses, ages, formation redshifts, etc. etc. We did not discuss systematic uncertainties in going from observational to physical quantities!!

Question Why do we keep discussing downsizing? Is it a surprise?

Question What are the best observational tests of importance of major gas-rich mergers at high redshift? (TJ Cox proposed low-z signature, but what about direct high-z observations -- simultaneous high- resolution imaging and IFU spectroscopy in rest-frame optical)

Question What would be smoking-gun proof of causal link between AGN and evolution of SF-history of massive galaxies? (Bundy AGN host mass function? Higher AGN fraction in z~2 massive galaxies?) Heckman presented evidence for the opposite, in local outflows with and without AGN contribution.

Question Are we any closer to answering the question “Big galaxies: what shuts them off?” Big piece of missing information: direct observations of gas content of galaxies (at most redshifts)

Question What is the best way to construct a comprehensive survey at z>1-3 to study massive galaxies while they are still growing (i.e. forming stars)? Sample definition and data collection, volume probed, number of objects. Or do we want to do detailed analysis of a smaller sample to determine physical processes?