On the Star Formation Histories of Massive Galaxies · On the Star Formation Histories of Massive...

On the Star Formation Histories of Massive Galaxies

Casey Papovich (Texas A&M University)Massive Galaxies through Cosmic Time 3, Tucson, AZ

credit: Volker Springel

Tuesday, November 9, 2010

• How and when do galaxies acquire their gas ?

• How is it converted to stars ?

-What are the Star Formation Histories of Galaxies ?

-What is the duty cycle of high-z star-forming galaxies ?

-When do galaxies assemble their stars? (Where do the stars form?)

Some Questions in the Formation of Massive Galaxies


What are the Star Formation Histories of Galaxies ?

Finlator, Davé, & Oppenheimer (2010, arXiv:1005.4066)



Finlator, Davé, & Oppenheimer (2010, arXiv:1005.4066)

SFR ∼ M*

high duty cycle

> 0d(SFR)

dt



K.-S. Lee, Dey, Reddy et al. (arXiv:1009.3022)

See also, Renzini (2009), Maraston et al. (2010), Lee et al. (2010).

Magn

itude

(AB)

Wavelength [micron]1 2 4 7 100.5

21

22

23

24

25

26

27

28

Stacked SEDs of z=3.7 galaxies.


Star-Formation and Mass Growth in High-z Galaxies

Finkelstein, Papovich, Giavalisco, Reddy, Ferguson, Dickinson(2010, ApJ, 719, 1250)


Do high redshift galaxies have Star Formation Histories that Rise with Time ?


Empirical Constraints on Star-Formation Histories and Mass Growth in High-z Galaxies

•Trace mass growth by comparing massive high-z galaxies at constant number density:

- track descendants and progenitors in galaxies in a relatively robust way (van Dokkum et al. 2010; similar to abundance matching Conroy & Weschler 2009)

- SFRs of galaxies with n=2 x 10-4 Mpc-3 increase from z=8 to z=3.

- galaxies with this number density have M=1.5 x 1011 M⊙ at z=0,

- star formation history of these galaxies matches stellar mass growth.


z=7.3 z=5.7 z=4.9

z=4.2 z=3.6 z=3.0

1 2 3 1 2 3 1 2 3Log (Mass / 1010 M⊙)

n(>

M)

[10-4

Mpc

-3]

3

2

1

0

3

2

1

0

Mass Functions and Halo Merger Trees from Millennium (Springel+05)

Track the Progenitors and Descendants of High-z Galaxies by Comparing at Constant Number Density


z=7.3 z=5.7 z=4.9

descendants of z=7.5 galaxies

z=4.2 z=3.6 z=3.0

1 2 3 1 2 3 1 2 3Log (Mass / 1010 M⊙)

n(>

M)

[10-4

Mpc

-3]

3

2

1

0

3

2

1

0

Mass Functions and Halo Merger Trees from Millennium (Springel+05)



Completeness = Fraction of selected galaxies with a progenitor selected at z=7.5 (descendant selected at z=3.0).

Similar results from simulations of the effects of mergers on mass functions (van Dokkum et al. 2010).

Progenitors of z=3 Galaxies

Descendants of z=7.5 Galaxies


Papovich, Finkelstein, Ferguson, Lotz, Giavalisco (2010, arXiv:1007.4554)


Integrated UV Luminosity Functions (Reddy & Steidel 2008; Bouwens et al. 2007, 2010).

Galaxy Populations selected at constant luminosity (or mass) correspond to very different number densities at different redshifts.

n=2x10-4 Mpc-3



Star Formation Histories of High-z Galaxies

SFH of galaxies with n(>LUV) = 2 x 10-4 Mpc-3

Dust

Corre

cted S

FR

Papovich, Finkelstein, Ferguson, Lotz, Giavalisco (2010, arXiv:1007.4554)

Daddi et al. 2005


Star Formation Histories of High-z GalaxiesStar Formation History of simulated galaxies show Rising SFRs

(Finlator, Davé, Papovich & Hernquist 2006, ApJ, 639, 672)

SFR ~ tα


Stellar Mass Growth of High-z Galaxies

Mass Growth of Galaxies

Masses of galaxies withn(>LUV) = 2 x 10-4 Mpc-3 (Shapley et al. 2005; Gonzalez et al. 2010;

Finkelstein et al. 2010)

Papovich, Finkelstein, Ferguson, Lotz,

Giavalisco (2010, arXiv:1007.4554)



Masses of galaxies withn(>M) = 2 x 10-4 Mpc-3

from stellar-mass functions(Marchesini et al. 2009)





Empirical Constraints on Star-Formation Histories and Mass Growth in High-z Galaxies

•Trace mass growth by comparing galaxies at constant number density:

- Massive galaxies have empirical star-formation histories that increase from z=8 to z=3.

- Basic agreement between empirical and theoretical SFHs.

- Star formation History of these galaxies matches stellar mass growth:

‣ if near unity “Duty cycle” of Star-formation,

‣ then high-mass end of IMF approximately Salpeter/Chabrier-like.

• Prediction: Star-formation and Mass growth predict Gas masses must Increase and that the Gas Accretion Rate tracks SFR.


What are the Star Formation Histories of Massive Galaxies?

Redshift

SFR

I. Period from 3 < z < 8 characterized by increasing SFRs.

II. Period from z < 3 with exponentially decreasing SFRs.

III


Where do stars form ?

When do they assemble into galaxies ?


Assembly Histories of Massive Galaxies

Oser, Ostriker, Naab, Johansson, & Burkert (arXiv:1010.1381)

See also talks by Ostriker and Naab tomorrow.

Log R / Rvir

-4 -3 -2 -1 0 1 2Ag

e [Gy

r]

02

0

0.3

0.6

11.5248

468

1012

RedshiftM

/ M

tot material

formed in situ

material accreted outside Rvir

total

in situ

accreted


Growth of Massive Galaxies at z < 2

z=2.0z=1.6z=1.1z=0.6

van Dokkum et al. (2010)

redshift0 0.5 1 1.5 2

10.6

10.8

11

11.2

11.4

Log

(M/M

⊙)

total mass

mass > 5 kpc

mass < 5 kpc


Summary: On the Star Formation Histories of Massive Galaxies

• Some convergence between Theory and Observations on Star Formation Histories.

‣ empirically, period at high redshifts 3 < z < 8 where SFRs increase with time.

‣ prediction that gas accretion rate also increases with time.

‣ period of declining SFRs at z <~ 3 in accord with observations of galaxy colors and stellar population ages.

‣ period at z < 3 possibly marked by rapid accretion of stars formed at large virial radii. Perhaps testable from metallicity gradients in early-type galaxies ?

Open questions:

-How and when do galaxies acquire their gas ?

-How well do we know the Duty Cycle of high-z star-forming galaxies ?

-What causes galaxies to stop forming stars ?


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