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Thick Disk Formation . Chris Brook, Hugo Martel, Vincent Veilleux Université Laval . Brad Gibson Swinburne University, Melbourne, Australia . Daisuke Kawata Carnegie Observatory . Introduction. -review our knowledge of thick disks

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thick disk formation

Thick Disk Formation

Chris Brook, Hugo Martel, Vincent Veilleux

Université Laval

Brad Gibson

Swinburne University, Melbourne, Australia

Daisuke Kawata

Carnegie Observatory

introduction
Introduction
  • -review our knowledge of thick disks
  • -show that our simulated gals have thin disk, thick disk, & stellar halo components
  • -thick disk formation in our simulated galaxies
  • -merger history of Milky Way sized gals
  • -properties of our simulated thick disks
  • -relationship to halo formation
  • -subsequent thin disk growth
thick disk info

Milky Way Thick Disk

  • Gilmore & Reid (`83)- star counts
  • scale height~0.6-1 kpc(e.g. Phelps et al `99)
  • ~5% of the mass of the thin disk
  • lags thin disk by ~ 40 km/s
  • dynamically hot
  • old ~10 Gyrs(e.g. Gilmore & Wyse `95)
  • -1<[Fe/H]<-0.2(peak~-0.6)
  • no vertical metallicity gradient
  • distinct chemical abundance patterns

Thick disk info

slide4

thin disk

thick disk

halo stars

□ dwarf spheroidal stars

Shetrone et al 2001, 2003

Geisler et al 2004

Venn et al. 2004

bensby abundance

thick disk stars

Bensby abundance

thin disk stars

Bensby et al `03

thick disk info2

Milky Way Thick Disk

  • Gilmore & Reid (`83)- star counts
  • large scale height~ 0.6-1 kpc (e.g. Phelps et al `99)
  • ~5% of the mass of the thin disk
  • lags thin disk by~40 km/s
  • dynamically hot
  • old stars ~10 Gyrs (e.g. Gilmore & Wyse `95)
  • -1<[Fe/H]<-0.2 (peak~-0.6)
  • no vertical metallicity gradient
  • distinct chemical abundance patterns

Thick disk info2

Kinematics, metal abundances and ages support the hypothesis it is a distinct component

exgal th disks

Extra-Galactic Thick Disks

photometric observations(Dalcanton & Bernstein `02)

  • thick disks common in disk galaxies
  • thick disk stars relatively old and metal rich
  • resolved stellar populations
  • (Mould `05; Davidge `05; Tikhonov `05;
  • Seth, Dalcanton & de Jong `05)
  • more evidence that thick disks are common
  • thick disk stars old, relatively metal rich
  • lack of vertical colour gradient
  • counter-rotating thick disk? (Yoachim & Dalcanton `05)

Exgal th disks

code details
Code details

GCD+: Details of the Code

  • parallel chemo-dynamical galaxy evolution code
  • tree N-body -DM & stars
  • SPH -gas
  • radiative cooling -metallicity (Sutherland & Dopita)
  • SFR ~ ρ1.5
  • supernovae feedback Ia (Kobayashi et al. 2000) & II
  • metal enrichment:
  • H, He, C, N, O, Ne, Mg, Si, Fe
  • SNII (Woosley & Weaver 1994)
  • Intermediate (van den Hoek & Groenewgen 1997)
  • SNIa (Iwamoto 1999)
velocity dispersion

Edvardsson 1993

Thick Disk?

Velocity dispersion

Nordstrom `04

+, x: simulations

gal 2 ev

Gal 2 ev

Abrupt increase in velocity dispersion, as well as period of rapid star formation, coincide with period of chaotic merging of gas rich building blocks, during which a central galaxy forms.

gal 2 ev16

Gal 2 ev

Abrupt increase in velocity dispersion, as well as period of rapid star formation, coincide with period of chaotic merging of gas rich building blocks, during which a central galaxy forms.

gal 2 ev17

Gal 2 ev

Abrupt increase in velocity dispersion, as well as period of rapid star formation, coincide with period of chaotic merging of gas rich building blocks, during which a central galaxy forms.

gal 2 ev18

Gal 2 ev

Abrupt increase in velocity dispersion, as well as period of rapid star formation, coincide with period of chaotic merging of gas rich building blocks, during which a central galaxy forms.

slide20

See also Zunter & Bullock `03

  • Number of merging building blocks vs lookback time.
  • >1010 Msun.
  • Contribute >4% mass of the halo (Quinn et al 1993)
  • Be merged by the next timestep
slide22

Simulations:

 z~1

□z~0.5

z=0

Brook, Kawata, Martel Gibson, Bailin, submittedto ApJ

Observations:

x z=0: Schwarzkopf & Dettmarr (`00)

o z~1: Reshetnikov, Dettmar & Combes (`03)

slide23

#1 T. Nykytyuk

Enhance star formation and infall of pre-enriched gas satisfy nicely the criteria set by Kim Venn.

Halo: Robertson et al. `05

scalelengths heights

Scalelengths/heights

+ thick

X thin

radius

Scale length:

Thin 4.1 kpc

Thick 2.6 kpc

Scale height:

Thin~ 0.5 kpc

Thick~ 1.2 kpc

slide25

Formation scenariosGilmore et al. (1989):

  • a slow, pressure supported collapse (Larson 1976);
  • Enhanced kinematic diffusion of the thin disk stellar orbits (Norris 1987);
  • a rapid dissipational violent dynamical heating of the early thin disk (Quinn et al. 1993, Jones & Wyse 1983);
  • direct accretion of thick disk material (Statler 1988)
  • collapse triggered by high metallicity (Wyse & Gilmore 1988).
  • -information of themetallicity,ages, andchemical abundancesof thick disk stars can be compared to the predictions that the various scenarios make.
slide26

scenario 2well supportedby Galactic observations (Quillen & Garret 2001; Wyse 2000; Gilmore et al. 2002; Freeman & Bland-Hawthorn 2002; Feltzing et al. 2003).

scenario 3 also has contemporary support from observations and simulations (Abadi et al. `03, Helmi et al. `05, Yoachim & Dalcanton `05, but see poster #60 Brooks & Governato, metallicity?)

Thick disk formation during the high redshift epoch of multiple mergers of gas rich building blocks is consistent with observations of the Milky Way and extra-galactic thick disks.

slide27

Thick disk and thin disk material are spatially well separated at high redshift

Support hierarchical models

Decoupled cores, counter-rotating disks

Two accretion events

slide32

Conclusions

Thick Disk: chemical abundance evidence suggest seperate formation from thin disk

(although ongoing research req’d)

Early heating of thin disk most accepted model (e.g. Freeman & Bland-Hawthorn 2000)

Recent observations suggest that old, metal rich thick disks are prevalent (perhaps even ubiquitous) in disk galaxies.

Our work suggests thick disk formed through chaotic merging of gas rich “building blocks” at high redshift.

cbrook@phy.ulaval.ca

http://www.astro.phy.ulaval.ca/CHRIS/chris.html

slide36

Disk

  • -overcooling
  • -angular momentum
  • -disk size
  • -feedback from AGN, supernovae, solar winds…
  • -multi-phase gas
  • -different recipes: thermal, kinematic, adiabatic feedback, subgrid physics
  • -resolution issues persist
  • -regulate star formation in earliest forming halos