Conference “Summary”
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Transcript of Conference “Summary”
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Conference “Summary”
Alice Shapley (Princeton)
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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.
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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
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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
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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?
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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)
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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?
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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.
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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)
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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?
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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)
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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.
Yan et al. 2006
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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
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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. 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 MBH- relation?
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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)
• ne, ionization parameter, ionizing spectrum (IMF, star-formation history)
• What does this tell us about nature of SF?(Erb et al. 2006a)
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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)
• ne, ionization parameter, ionizing spectrum (IMF, star-formation history)
• What does this tell us about nature of SF?(Kriek et al. 2006)
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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!!
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Question• Why do we keep discussing downsizing? Is it a surprise?
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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)
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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.
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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)
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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?