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Island Universes: Structure and Evolution of Disk Galaxies

Island Universes: Structure and Evolution of Disk Galaxies. Early career: radio continuum work Late 70’s: focus on optical data Key contributions to our understanding of disk galaxies: Truncation at ~4 scale-lengths Constant vertical scale-height

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Island Universes: Structure and Evolution of Disk Galaxies

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  1. Island Universes: Structure and Evolution of Disk Galaxies

  2. Early career: radio continuum work Late 70’s: focus on optical data Key contributions to our understanding of disk galaxies: Truncation at ~4 scale-lengths Constant vertical scale-height Pioneering stellar kinematics Supervision of number of high-quality PhD theses Major influence on development of astronomy on (inter)national level In the footsteps of Kapteyn

  3. A foray into statistics

  4. This Conference • Many new (and some old) results on disk galaxies • Disk galaxies are quite complex ‘Island Universes’ • They are key to galaxy formation process • Significant challenge to theory • Brief summary restricted to some highlights • Structure and properties of stellar disks • Thick disks, bulges, bars, peanuts & other components • Expanding horizons: panchromatic surveys to high z • Outlook

  5. Stellar Disks • Gospel by Freeman (1970) and by van der Kruit & Searle (1981-2) re-addressed and extended • Three types of surface brightness profile (Pohlen) • Pure exponential, sometimes to 9 disk scale-lengths • Double exponential, like vdK+S truncation (Freeman II) • Idem, but outer slope shallower than inner one • Ratio of scale lengths constant out to z~1(Perez) • Studies of ~face-on and edge-on disks disagree? • Fractions of three different types need to be checked • Try to do this in much larger samples (SDSS/MGC)

  6. Outer Regions • Heroic star counts in M31 (Ferguson/Guhathakurta) • Very extended structure (>50 kpc) • Disk or metal-poor halo? • Spectroscopy: kinematics, [Fe/H] • UV & H evidence for faint outer disks (Zaritsky) • Origin of these components? • Star formation threshold? • Is there a link with presence of HI warp or flare? • Origin of warps most likely connected to torque caused by local cosmic inflow pattern (Binney)

  7. Dark halos, kinematics, and M/L • HI studies of dark halo now ‘mature’ • Some work seems stalled in ‘cusp wars’: time to refocus • Key development: determine (M/L) of disk • Measure vertical velocity dispersion • Breaks the degeneracy between stellar vs halo mass • Builds on Piet’s early work, followed by Bottema • IFU spectroscopy can constrain shape of velocity ellipsoid and value of (M/L) (Verheyen/Bershady) • Compare with (M/L) from colors/linestrengths • Sets limits on IMF (de Jong/Bell) • Specific angular momentum content of halo (Kassin)

  8. Other Components • Classical picture of thin disk + R1/4-bulge embedded in dark halo is now more complicated • Thick disks are ubiquitous • Majority of disk galaxies are barred (~70%) • Much confusion about the central regions: • Classical and ‘pseudo’-bulges, bars and peanuts • Neutral and ionized gas in halos • Not discussed: central black holes in disks

  9. Thick disks • Most disk galaxies have additional, thick, disk (Yoachim/Dalcanton) • Modest mass fraction, but increases below vc~120 km/s • Some counter-rotate:  external origin • Heavier counter-rotating disks seen in S0s • [/Fe] vs [Fe/H] in MW thick disk  it cannot have formed by accretion of small stellar lumps (Venn) • Origin in gas-rich merger (cf Sommer-Larsen)

  10. Bars • Bar influences dynamics and star formation activity • They drive gas to the center (and so do interactions) • This can trigger starburst, sometimes in ring • Bars slow down and change shape due to friction by halo (Sellwood/Athanassoula) • Consistent with ~constant bar fraction since z~1? (Bell) • Bars do not transform into bulges today (Elmegreen) • End-on peanut looks like bulge (Bureau)

  11. Impostor Bulges? • Traditional bulges may be mix of structures • Some classical bulges similar to E/S0s • Nearly 50% of bulges have exponential profiles, and may be disks; these all have central star clusters • In many cases the central bar may be the bulge; it may have an embedded central disk (cf Milky Way) • Not clear at all which of these have central black hole • Some classification schemes tied to prejudices about formation scenario • Definition of ‘pseudo-bulge’ needs further clarification

  12. Extended extraplanar gas HI (Fraternali) H and X-rays (Dettmar) Properties consistent with theory of fountains/winds Not evident that in situ star formation is needed in halo Effect of run-away stars to be investigated Baryonic Halo HI in NGC 891 Oosterloo, Fraternali, Sancisi 2005

  13. The Milky Way • Piet measured scale-length of MW disk • Based on Pioneer 10 data • This is Paper V in the legendary series (but vdK only) • Generated follow-up work to measure run of  with R • Milky Way received relatively little attention here • Kinematics of disk stars (Binney) • Stellar halo not formed by dissolving present-day like dSph’s, dIrr, of LMC-clones (Venn) • Comparison of MW properties with simulations: key test of formation paradigm (Bullock/Sommer-Larsen)

  14. Panchromatic Surveys • Beautiful multi-wavelength high-resolution imaging • From UV (GALEX) via HST to Spitzer and HI/CO • Kennicutt, Regan, Murphy/Braun et al. • Systematic representative surveys (e.g. SINGS) • Separation of stars and different types of dust • Still to be linked with NIR extinction method (Alves) • Get full SED’s, star formation rates, CR structure • Images constrain lifetime of embedded phase of massive star formation • Key challenge is to model all this in detail (Dopita)

  15. 0.15 mm 0.4-0.8 mm 1.2-2.2 mm 3.6 mm 8.0 mm 24 mm 70 mm 160 mm

  16. WPFC2/F336W/F555W/F675W Integral-field Spectroscopy NGC 7742 (Falcon-Barroso)

  17. Studies to high redshift • Much work on properties of galaxies to high z • Be careful with selection biases (Vogt) • Most objects found: progenitors of present-day spheroids (Pettini) • Disks detected to z~2 (Abraham/Kassin) • DLA hosts resemble local galaxies with HI (Zwaan) • Inside-out formation (Bell/Trujillo) • Evolution of population  evolution of objects (Bell) • Metallicity determinations to z~3 • Much progress for disks (Kewley) • Also for the ISM, via DLA’s (Fall) • Beware of selection effects

  18. The Future • Studies of resolved stellar populations in MW and Local Group galaxies hold much promise • Panchromatic surveys complemented with IFU spectroscopy in optical and IR, to high z • Theoretical models & simulations need to fit observations in detail; this is within reach • Herschel, ALMA, GAIA and JWST to come • Much scope for more pioneering work by Piet

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