Island Universes: Structure Island Universes: Structure and Evolution of Disk and Evolution of Disk

GalaxiesGalaxies

In the footsteps of KapteynIn the footsteps of Kapteyn Early career: radio continuum work Early career: radio continuum work

Late 70’s: focus on optical dataLate 70’s: focus on optical data

Key contributions to our Key contributions to our understanding of disk galaxies:understanding of disk galaxies:– Truncation at ~4 scale-lengthsTruncation at ~4 scale-lengths– Constant vertical scale-heightConstant vertical scale-height– Pioneering stellar kinematicsPioneering stellar kinematics

Supervision of number of Supervision of number of high-quality PhD theses high-quality PhD theses

Major influence on development of Major influence on development of astronomy on (inter)national level astronomy on (inter)national level

A foray A foray into into

statisticsstatistics

This ConferenceThis Conference

Many new (and some old) results on disk galaxiesMany new (and some old) results on disk galaxies– Disk galaxies are quite complex ‘Island Universes’Disk galaxies are quite complex ‘Island Universes’– They are key to galaxy formation processThey are key to galaxy formation process– Significant challenge to theorySignificant challenge to theory

Brief summary restricted to some highlightsBrief summary restricted to some highlights– Structure and properties of stellar disksStructure and properties of stellar disks– Thick disks, bulges, bars, peanuts & other componentsThick disks, bulges, bars, peanuts & other components– Expanding horizons: panchromatic surveys to high zExpanding horizons: panchromatic surveys to high z

OutlookOutlook

Stellar DisksStellar Disks Gospel by Freeman Gospel by Freeman (1970)(1970) and by van der Kruit & and by van der Kruit &

Searle Searle (1981-2)(1981-2) re-addressed and extended re-addressed and extended

Three types of surface brightness profile Three types of surface brightness profile (Pohlen)(Pohlen) – Pure exponential, sometimes to 9 disk scale-lengthsPure exponential, sometimes to 9 disk scale-lengths– Double exponential, like vdK+S truncation (Freeman Double exponential, like vdK+S truncation (Freeman IIII))– Idem, but outer slope shallower than inner oneIdem, but outer slope shallower than inner one

Ratio of scale lengths constant out to Ratio of scale lengths constant out to z~1z~1 (Perez)(Perez)

Studies of ~face-on and edge-on disks disagree? Studies of ~face-on and edge-on disks disagree? – Fractions of three different types need to be checkedFractions of three different types need to be checked– Try to do this in much larger samples (SDSS/MGC)Try to do this in much larger samples (SDSS/MGC)

Outer Regions Outer Regions Heroic star counts in M31 Heroic star counts in M31

(Ferguson/Guhathakurta)(Ferguson/Guhathakurta) – Very extended structure (>50 kpc)Very extended structure (>50 kpc)– Disk or metal-poor halo? Disk or metal-poor halo? – Spectroscopy: kinematics, [Fe/H]Spectroscopy: kinematics, [Fe/H]

UV & HUV & H evidence for faint evidence for faint outer disks outer disks (Zaritsky)(Zaritsky)

Origin of these components? Origin of these components? – Star formation threshold?Star formation threshold?– Is there a link with presence of HI warp or flare?Is there a link with presence of HI warp or flare?

Origin of warps most likely connected to torque Origin of warps most likely connected to torque caused by local cosmic inflow pattern caused by local cosmic inflow pattern (Binney)(Binney)

Dark halos, kinematics, and Dark halos, kinematics, and M/LM/L

HI studies of dark halo now ‘mature’ HI studies of dark halo now ‘mature’ – Some work seems stalled in ‘cusp wars’: time to refocusSome work seems stalled in ‘cusp wars’: time to refocus

Key development: determine (M/L)Key development: determine (M/L) of disk of disk– Measure vertical velocity dispersionMeasure vertical velocity dispersion– Breaks the degeneracy between stellar vs halo massBreaks the degeneracy between stellar vs halo mass– Builds on Piet’s early work, followed by BottemaBuilds on Piet’s early work, followed by Bottema

IFU spectroscopy can constrain shape of velocity IFU spectroscopy can constrain shape of velocity ellipsoid and value of (M/L)ellipsoid and value of (M/L) ( (Verheyen/Bershady)Verheyen/Bershady)

Compare with (M/L)Compare with (M/L) from colors/linestrengths from colors/linestrengths– Sets limits on IMF (de Jong/Bell)Sets limits on IMF (de Jong/Bell)– Specific angular momentum content of halo (Kassin)Specific angular momentum content of halo (Kassin)

Other ComponentsOther Components

Classical picture of thin disk + RClassical picture of thin disk + R1/41/4-bulge -bulge embedded in dark halo is now more complicatedembedded in dark halo is now more complicated

Thick disks are ubiquitousThick disks are ubiquitous

Majority of disk galaxies are barred (~70%)Majority of disk galaxies are barred (~70%)

Much confusion about the central regions: Much confusion about the central regions: – Classical and ‘pseudo’-bulges, bars and peanutsClassical and ‘pseudo’-bulges, bars and peanuts

Neutral and ionized gas in halosNeutral and ionized gas in halos

Not discussed: central black holes in disksNot discussed: central black holes in disks

Thick disksThick disks Most disk galaxies have additional, thick, disk Most disk galaxies have additional, thick, disk

(Yoachim/Dalcanton)(Yoachim/Dalcanton)– Modest mass fraction, Modest mass fraction,

but increases below but increases below vvcc~120 km/s~120 km/s

– Some counter-rotate: Some counter-rotate: external origin external origin

– Heavier counter-rotating Heavier counter-rotating disks seen in S0sdisks seen in S0s

[[/Fe] vs [Fe/H] in MW thick disk /Fe] vs [Fe/H] in MW thick disk it cannot have it cannot have formed by accretion of small stellar lumps formed by accretion of small stellar lumps (Venn)(Venn)

Origin in Origin in gas-richgas-rich merger merger (cf Sommer-Larsen)(cf Sommer-Larsen)

BarsBars Bar influences dynamics and star formation activityBar influences dynamics and star formation activity

– They drive gas to the center (and so do interactions)They drive gas to the center (and so do interactions)– This can trigger starburst, sometimes in ring This can trigger starburst, sometimes in ring

Bars slow down and change shape due to friction Bars slow down and change shape due to friction by halo by halo (Sellwood/Athanassoula)(Sellwood/Athanassoula)

– Consistent with ~constant bar fraction since z~1? (Bell)Consistent with ~constant bar fraction since z~1? (Bell)

Bars do not transform into bulges today Bars do not transform into bulges today (Elmegreen)(Elmegreen)

– End-on peanut looks like bulge (Bureau)End-on peanut looks like bulge (Bureau)

Impostor Bulges?Impostor Bulges? Traditional bulges may be mix of structuresTraditional bulges may be mix of structures

– Some classical bulges similar to E/S0sSome classical bulges similar to E/S0s– Nearly 50% of bulges have exponential profiles, and may Nearly 50% of bulges have exponential profiles, and may

be disks; these all have central star clusters be disks; these all have central star clusters – In many cases the central bar may be the bulge; it may In many cases the central bar may be the bulge; it may

have an embedded central disk (cf Milky Way)have an embedded central disk (cf Milky Way)– Not clear at all which of these have central black holeNot clear at all which of these have central black hole

Some classification schemes tied to prejudices Some classification schemes tied to prejudices about formation scenarioabout formation scenario– Definition of ‘pseudo-bulge’ needs further clarificationDefinition of ‘pseudo-bulge’ needs further clarification

Baryonic HaloBaryonic Halo Extended extraplanar gasExtended extraplanar gas

– HI (Fraternali)HI (Fraternali)– HH and X-rays (Dettmar) and X-rays (Dettmar)

Properties consistent with Properties consistent with theory of fountains/winds theory of fountains/winds – Not evident that in situ star Not evident that in situ star

formation is needed in haloformation is needed in halo– Effect of run-away stars to Effect of run-away stars to

be investigatedbe investigated

Oosterloo, Fraternali, Sancisi 2005Oosterloo, Fraternali, Sancisi 2005

HI in NGC 891HI in NGC 891

The Milky WayThe Milky Way Piet measured scale-length of MW diskPiet measured scale-length of MW disk

– Based on Pioneer 10 dataBased on Pioneer 10 data– This is Paper This is Paper VV in the legendary series (but vdK only) in the legendary series (but vdK only)– Generated follow-up work to measure run of Generated follow-up work to measure run of with R with R

Milky Way received relatively little attention hereMilky Way received relatively little attention here– Kinematics of disk stars (Binney)Kinematics of disk stars (Binney)– Stellar halo not formed by dissolving present-day like Stellar halo not formed by dissolving present-day like

dSph’s, dIrr, of LMC-clones (Venn)dSph’s, dIrr, of LMC-clones (Venn)– Comparison of MW properties with simulations: key test Comparison of MW properties with simulations: key test

of formation paradigm (Bullock/Sommer-Larsen)of formation paradigm (Bullock/Sommer-Larsen)

Panchromatic SurveysPanchromatic Surveys Beautiful multi-wavelength high-resolution imagingBeautiful multi-wavelength high-resolution imaging

– From UV (GALEX) via HST to Spitzer and HI/CO From UV (GALEX) via HST to Spitzer and HI/CO – Kennicutt, Regan, Murphy/Braun et al.Kennicutt, Regan, Murphy/Braun et al.

Systematic representative surveys (e.g. SINGS)Systematic representative surveys (e.g. SINGS)– Separation of stars and different types of dust Separation of stars and different types of dust – Still to be linked with NIR extinction method (Alves)Still to be linked with NIR extinction method (Alves)– Get full SED’s, star formation rates, CR structureGet full SED’s, star formation rates, CR structure– Images constrain lifetime of embedded phase of Images constrain lifetime of embedded phase of

massive star formationmassive star formation

Key challenge is to model all this in detail Key challenge is to model all this in detail (Dopita)(Dopita)

0.15 m 0.4-0.8 m 1.2-2.2 m 3.6 m

8.0 m 24 m 70 m 160 m

Integral-field SpectroscopyIntegral-field Spectroscopy

WPFC2/F336W/F555W/F675WWPFC2/F336W/F555W/F675W

(Falcon-Barroso)(Falcon-Barroso)

NGC 7742NGC 7742

Studies to high redshiftStudies to high redshift Much work on properties of galaxies to high zMuch work on properties of galaxies to high z

– Be careful with selection biases (Vogt)Be careful with selection biases (Vogt)– Most objects found: progenitors of present-day Most objects found: progenitors of present-day

spheroids (Pettini)spheroids (Pettini)– Disks detected to z~2 (Abraham/Kassin)Disks detected to z~2 (Abraham/Kassin)– DLA hosts resemble local galaxies with HI (Zwaan)DLA hosts resemble local galaxies with HI (Zwaan)– Inside-out formation (Bell/Trujillo)Inside-out formation (Bell/Trujillo)– Evolution of population Evolution of population evolution of objects (Bell) evolution of objects (Bell)

Metallicity determinations to z~3Metallicity determinations to z~3– Much progress for disks (Kewley)Much progress for disks (Kewley)– Also for the ISM, via DLA’s (Fall) Also for the ISM, via DLA’s (Fall) – Beware of selection effectsBeware of selection effects

The FutureThe Future Studies of resolved stellar populations in MW Studies of resolved stellar populations in MW

and Local Group galaxies hold much promiseand Local Group galaxies hold much promise

Panchromatic surveys complemented with IFU Panchromatic surveys complemented with IFU spectroscopy in optical and IR, to high zspectroscopy in optical and IR, to high z

Theoretical models & simulations need to fit Theoretical models & simulations need to fit observations in detail; this is within reachobservations in detail; this is within reach

Herschel, ALMA, GAIA and JWST to comeHerschel, ALMA, GAIA and JWST to come

Much scope for more pioneering work by Piet Much scope for more pioneering work by Piet