AndreyAndrey

KravtsovKravtsov The University of ChicagoThe University of Chicago

withwith

Nick Nick GnedinGnedin((Fermilab/U.ChicagoFermilab/U.Chicago)) Kostas Kostas TassisTassis

(JPL)(JPL)

The chemistry of galaxy formation:environmental dependence of the Schmidt-Kennicutt relation

and implications for galaxy evolution

GnedinGnedin, , TassisTassis & & KravtsovKravtsov 2009, 2009, ApJApJ 697, 55697, 55GnedinGnedin & & KravtsovKravtsov 2010, 2010, ApJApJ in press (arXiv/0912.3005)in press (arXiv/0912.3005)

GnedinGnedin & & KravtsovKravtsov 2010, 2010, ApJApJ submitted (arXiv/1004.0003)submitted (arXiv/1004.0003)

what are we trying to do?generally speaking, to figure out how galaxies form and evolve…

i.e., the hierarchical merging, gas accretion (cold/hot), and conversion of gas into stars (aka star formation)

+ whatever feedback processes are relevantstandard recipe for star formation in simulations

Incorrect galaxies formed: bulges too big, angular momentum too small, etc., etc.

new recipe based on H2 as a tracer of star forming regions with empirically motivated efficiency (~1% per free fall time):

more realistic galaxies (cf. next talk by Oscar Agertz)

+ arbitrary thresholds for T and gas density (constant in time and space)

“on the fly” treatment of H2 in cosmological simulations

spatial resolution ~20-50 pc (physical; slowly changing with redshift)

H2 formation of dust grains/destruction by UV with a model for approximate H2 self-shielding and shielding by dust, assuming dust-to-gasratio scales linearly with metallicity of the gas

see see GnedinGnedin, , TassisTassis, , KravtsovKravtsov2009, 2009, ApJApJ 697, 55 697, 55

and and GnedinGnedin & & KravtsovKravtsov 2010 2010 2010, 2010, ApJApJ submitted (arXiv/1004.0003)submitted (arXiv/1004.0003)

blueblue = HI= HI

ffH2H2 > 0.5> 0.5red = molecular gas

500

kpc

(com

ov.)

500

kpc

(com

ov.)

50 k

pc10

kpc

ionization by cosmic and localinterstellar UV flux (on the fly RT

using OTVET approximation)on the fly atomic andmolecular chemistry

+ dust chemistry

MultiMulti--phase ISM in simulated galaxiesphase ISM in simulated galaxiestemperature-density diagram: main phases of the ISM are

reproduced in our galaxy formation simulations

GnedinGnedin, N., , N., TassisTassis, , KravtsovKravtsov2009, 2009, ApJApJ 697, 55697, 55

“on the fly” treatment of H2 in cosmological simulations

spatial resolution ~20-50 pc (physical; slowly changing with redshift)

H2 formation of dust grains/destruction by UV with a model for approximate H2 self-shielding and shielding by dust, assuming dust-to-gasratio scales linearly with metallicity of the gas

see see GnedinGnedin, , TassisTassis, , KravtsovKravtsov2009, 2009, ApJApJ 697, 55 697, 55

and and GnedinGnedin & & KravtsovKravtsov 2010 2010 2010, 2010, ApJApJ submitted (arXiv/1004.0003)submitted (arXiv/1004.0003)

blueblue = HI= HI

ffH2H2 > 0.5> 0.5red = molecular gas

500

kpc

(com

ov.)

500

kpc

(com

ov.)

50 k

pc10

kpc

ionization by cosmic and localinterstellar UV flux (on the fly RT

using OTVET approximation)on the fly atomic andmolecular chemistry

+ dust chemistry

Tracking abundance of species of H, He, and HTracking abundance of species of H, He, and H22

GnedinGnedin & & KravtsovKravtsov 2010 2010 2010, 2010, ApJApJ submitted (arXiv/1004.0003)submitted (arXiv/1004.0003)

Molecular fraction as a function of gas densityMolecular fraction as a function of gas density

the trends approximated by:the trends approximated by:

Strong trends with metallicity (dust-to-gas ratio) and ambient UV flux

GnedinGnedin & & KravtsovKravtsov2010 2010 ApJApJ submittedsubmitted(arXiv/1004.0003)(arXiv/1004.0003)

DDMWMW = dust= dust--toto--gas ratio gas ratio in units of the MW valuein units of the MW value

UUMWMW = interstellar UV flux at 1000 A= interstellar UV flux at 1000 Ain units of the MW valuein units of the MW value

smaller dustsmaller dust--toto--gasgasratios Dratios D

HIHI-->>H2H2 transition shifts transition shifts to higher densities forto higher densities for

larger FUV flux Ularger FUV flux U

mol

ecul

ar fr

actio

n

GnedinGnedin, N., , N., TassisTassis, , KravtsovKravtsov 2009, 2009, ApJApJ 697, 55; 697, 55; GnedinGnedin & & KravtsovKravtsov 2010, 2010, ApJApJ submitted (arXiv/1004.0003)submitted (arXiv/1004.0003)

also also KrumholzKrumholz et al. 2009, et al. 2009, ApJApJ 693, 216; 693, 216; ApJApJ 701, L12701, L12McKee & McKee & KrumholzKrumholz 2010, 2010, ApJApJ 709, 308 709, 308

HI+H2 column density

mol

ecul

ar fr

actio

nModel is tuned to reproduce observed trend of molecular Model is tuned to reproduce observed trend of molecular

fraction with gas column density fraction with gas column density in MW, LMC, and SMCin MW, LMC, and SMC

Sensitivity of the SK relation to FUV flux and Sensitivity of the SK relation to FUV flux and dustdust--toto--gas ratiogas ratio

test models simulated to z=3 but with different fixed dusttest models simulated to z=3 but with different fixed dust--toto--gas ratios and gas ratios and interstellar UV fluxes show that the main difference is gas interstellar UV fluxes show that the main difference is gas metallicitymetallicity

GnedinGnedin & & KravtsovKravtsovarXiv/1004.0003arXiv/1004.0003

varying varying dustdust--toto--gas ratiogas ratio

varying varying interstellar UV fluxinterstellar UV flux

observed:observed:BigielBigiel et al. 2008et al. 2008

((graygray band)band)

observed:observed:KennicuttKennicutt 1998 fit1998 fitsfrsfr --HIHI

sfrsfr --H2H2 model:model:sfrsfr --HI+H2HI+H2Z=0.1ZsunZ=0.1ZsunZ=0.3ZsunZ=0.3Zsun

Z=Z=ZsunZsun

z=0 SK relation z=0 SK relation

SchmidtSchmidt--KennicuttKennicutt

relation relation for simulated galaxies @ z=3 for simulated galaxies @ z=3

comparison with star formation constraints in the DLA and LBG sycomparison with star formation constraints in the DLA and LBG systems stems by Wolfe & Chen (2006) and by Wolfe & Chen (2006) and RafelskiRafelski et al. (2010)et al. (2010)

surface densitiessurface densitiesare measuredare measured

in 500 pc patchesin 500 pc patches

sfrsfr --H2H2

model:model:sfrsfr --HI+H2HI+H2Z~0.3ZsunZ~0.3ZsunZ~0.1ZsunZ~0.1Zsun

sfrsfr --HIHI

KennicuttKennicutt ‘‘98 fit98 fit

observations:observations:Wolfe &Chen 06Wolfe &Chen 06

upper limitsupper limits

GnedinGnedin & & KravtsovKravtsov2010 2010 ApJApJ in pressin press(arXiv/0912.3005) (arXiv/0912.3005) RafelskiRafelski+ 09+ 09

RafelskiRafelski et al. 2010et al. 2010measurementmeasurement

cB58 LBG galaxycB58 LBG galaxy(Baker et al. 2004)(Baker et al. 2004)

comparison with observations at z~3comparison with observations at z~3--44

GnedinGnedin & & KravtsovKravtsov 2009, 2009, ApJApJ in press (arXiv/0912.3005)in press (arXiv/0912.3005)

galaxy formation simulations with selfgalaxy formation simulations with self--consistent consistent evolution of evolution of metallicitymetallicity, dust, dust--toto--gas, UV field, gas, UV field,

and nonand non--equilibrium H2 formationequilibrium H2 formation

datadata: : ManucciManucci et al. 2009; et al. 2009; ErbErb et al. 2006; et al. 2006; PettiniPettini et al. 2001; Stark et al. 2009et al. 2001; Stark et al. 2009colocoloredred pointspoints = galaxies in simulations = galaxies in simulations

Some implications of the inefficiency of gas conversion into Some implications of the inefficiency of gas conversion into stars in lowstars in low--metallicitymetallicity, high, high--redshiftredshift

galaxiesgalaxies

new mechanism for suppressing star formation in halos at high znew mechanism for suppressing star formation in halos at high z

z=3z=3

GnedinGnedin & & KravtsovKravtsov2010, 2010, ApJApJ in pressin press(arXiv/0912.3005)(arXiv/0912.3005)

strong implications for the prevalence of highstrong implications for the prevalence of high--z disks, clumpy galaxies at z disks, clumpy galaxies at z~1z~1--2, morphological evolution at z<2 (formation of galaxies with re2, morphological evolution at z<2 (formation of galaxies with realistic alistic

bulgebulge--toto--disk ratios)disk ratios)

SummarySummary Different (steepening at higher gas ) Schmidt-Kennicutt relation is predicted for lower-metallicity, high-UV field environments of high-z galaxies. This is consistent with and explains observational constraints on the z~3 S-K relation (Wolfe & Chen 2006; Rafelski et al. 2010).

Our results have many interesting implications for galaxy formation, and interpretation of high-z observations, e.g.:

sizes of high-z galaxies predicted by models, which use z=0 S-K relation, are l ikely overestimated by a factor of >2. Sizes may evolve simply because metallicity of the disk increases.

inefficient (slow) formation of H2 in low-mass, low-metallicity high-z halos can lead to a delay or suppression of star formation even in halos with Tvir>104 K(which leave such objects gas rich and quite dark until lower redshifts)

this should make most of the mergers for MW-sized progenitors gas-rich andmake the disks more resilient to mergers (explaining prevalence of thin stellar disks at low z) and more realistic bulge-to-gas ratios (cf. next talk)

GnedinGnedin, , TassisTassis & & KravtsovKravtsov 2009, 2009, ApJApJ 697, 55697, 55GnedinGnedin & & KravtsovKravtsov 2010, 2010, ApJApJ in press (arXiv/0912.3005)in press (arXiv/0912.3005)

GnedinGnedin & & KravtsovKravtsov 2010, 2010, ApJApJ submitted (arXiv/1004.0003)submitted (arXiv/1004.0003)