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Conference “Summary”

Conference “Summary”. Alice Shapley (Princeton). Overview.

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Conference “Summary”

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  1. Conference “Summary” Alice Shapley (Princeton)

  2. 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.

  3. 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

  4. 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

  5. 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?

  6. 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)

  7. Observations up to z~1: CMR vs. dynamics • CMR in clusters at z~0.4-0.8. Lack of faint red galaxies at higher redshifts (consistent with Bundy et al., or in general at z~0.8)? • CMR evolution at z~0.4-0.8 indicates zform~3 for stars in bright red galaxies • Dynamical studies (evolution of FP to z~0.5) indicate zform=2.0 for M>1011Msun • Are these two results consistent?

  8. 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.

  9. 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)

  10. 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?

  11. 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)

  12. Yan et al. 2006 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 zform~2-3.

  13. 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

  14. Observations Beyond z~1 • ~20-25% of M>1011Msun 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 fewx1010 Msun. InUV-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 MBH- relation?

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

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

  17. 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!!

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

  19. 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)

  20. 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.

  21. 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)

  22. 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?

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