Island Universes: Structure and Evolution of Disk Galaxies

1
Island Universes Structure and Evolution of Disk
Galaxies
2
In the footsteps of Kapteyn

• Early career radio continuum work
• Late 70s 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

3
(No Transcript)
4
A foray into statistics
5
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

6
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 vdKS truncation
  (Freeman II)
• Idem, but outer slope shallower than inner one
• Ratio of scale lengths constant out to z1
  (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)

7
Outer Regions

• Heroic star counts in M31 (Ferguson/Guhathakurt
  a)
• Very extended structure (gt50 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)

8
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 Piets 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)

9
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

10
Thick disks

• Most disk galaxies have additional, thick, disk
  (Yoachim/Dalcanton)
• Modest mass fraction,
  but increases below
  
  vc120 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)

11
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 z1?
  (Bell)
• Bars do not transform into bulges today
  (Elmegreen)
• End-on peanut looks like bulge (Bureau)

12
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

13
Baryonic Halo

• 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

HI in NGC 891
Oosterloo, Fraternali, Sancisi 2005
14
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 dSphs, dIrr, of LMC-clones (Venn)
• Comparison of MW properties with simulations key
  test of formation paradigm (Bullock/Sommer-Larsen)
  

15
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 SEDs, 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)

16
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
17
Integral-field Spectroscopy
NGC 7742
(Falcon-Barroso)
18
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 z2 (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 z3
• Much progress for disks (Kewley)
• Also for the ISM, via DLAs (Fall)
• Beware of selection effects

19
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