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The natural emergence of the SFR-H2 surface density relation in - - PowerPoint PPT Presentation
The natural emergence of the SFR-H2 surface density relation in - - PowerPoint PPT Presentation
The natural emergence of the SFR-H2 surface density relation in galaxy simulations Alessandro Lupi (Institut dAstrophysique de Paris) THE ROLE OF GAS IN GALAXY DYNAMICS with: S. Bovino, P. R. Capelo, M. Volonteri, J. Silk October 2nd, 2017
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Standard prescription: H2-based prescription:
(Gnedin+09, Christensen+12, Hopkins+14, Tomassetti+15, Pallottini+17, Hopkins+17)
H2-based star formation
ρg > ρg,thr (Tg < Tg,thr)
BUT
Recent theoretical studies have revealed a lack of causal connection between H2 and SF (Krumholz et al. 2011, Clark et al. 2012). The formation of H2 is controlled by SF, or, in general, by the gravitational collapse of atomic gas, not vice versa (Mac Low 2016).
MORE LIKELY
˙ ρSF = ερgas tff ˙ ρSF = ε0fH2 ρgas tff
October 2nd, 2017 University of Malta
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(Turbulent magnetized clouds)
Star formation model
ps(s) = 1 p 2πσ2
s
exp[−(s − s0)2 2σ2
s
]
Padoan & Nordlund 2011
σ2
s = ln(1 + b2M2)
The critical density for SF is related to the magnetic shock jump conditions and to the magnetic critical mass for collapse
scrit = ln ⇥ 0.067θ−2αvirM2⇤ " = ✏? 2t exp(3 82
s)
" 1 + erf 2
s − scrit
p 22
s
!# αvir = 5σ2
vL/(6GMcloud)
Federrath & Klessen 2012
October 2nd, 2017 University of Malta
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Physically motivated SF SN feedback + Mass losses from low-mass stars Interstellar radiation field Clumping factor
Numerical setup
Galaxy with typical z=3 properties NFW DM halo + exp. decay: Rvir = 45 kpc Mhalo = 2x1011 M⦿ Stellar + gaseous disc: R0 = 1.28 kpc Mstar = 1.6x109 M⦿ ; Mgas = 2.4x109 M⦿ Hernquist stellar bulge: a = 0.256 kpc Mbulge = 8x108 M⦿ Evolved for 400 Myr in isolation GIZMO mesh-less finite mass KROME Non-eq. chemistry (Photochemistry)
GIZMO-KROME
October 2nd, 2017 University of Malta
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The Interstellar radiation field
We implemented two sub-grid models and compared them with a full-RT simulation. Model ‘S’ τ = σeff mH (ρgRmax |rρg|R2
max/2)
F = X
i
Li,? 4πd2
i
exp(−τi) lSob = ρg |rρg| τ = X
j
σj,binnjλ
October 2nd, 2017 University of Malta
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The Interstellar radiation field
Model ‘T’ lSob = ρg |rρg| F = "X
i
Li,? 4πd2
i
exp(−τi) # exp(−τg) Around star: Around gas: λJ = √πcs √Gρ
October 2nd, 2017 University of Malta
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RT in GIZMO
Momentum method with M1 closure scheme (Rosdahl et al. 2013) 1 c ∂Iν ∂t + n · rIν = Sν kνIν ∂N⌫ ∂t + r · F⌫ = N ?
⌫ k⌫cN⌫
∂F⌫ ∂t + c2r · P⌫ = k⌫cF⌫ Hopkins et al. (in preparation)
October 2nd, 2017 University of Malta
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The clumping factor
Rf(H2) = 3 × 1017nHtotntotZ/Z cm3s1 hRf(H2)i = 3 ⇥ 1017hnHtotntotiZ/Z cm3s1 hRf(H2)i = 3 ⇥ 1017hnHtotihntotiCρZ/Z cm3s1 PDF averaged rate Express using average density Cρ = hρ2i hρi2 = exp(σ2
s) = 1 + b2M2
October 2nd, 2017 University of Malta
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The effect of the interstellar radiation
G_RAD_S G_RT G_RAD_T
4 2 2 4
log nHtot (cm3)
1 2 3 4 5 6 7
log T(K)
103 104 105 106 107
M (M)
4 2 2 4
log nHtot (cm3)
6 5 4 3 2 1
log fH
103 104 105 106 107
M (M)
4 2 2 4
log nHtot (cm3)
0.0 0.2 0.4 0.6 0.8 1.0
fH2
103 104 105 106 107
M (M)
4 2 2 4
log nHtot (cm3)
0.0 0.2 0.4 0.6 0.8 1.0
fH2
103 104 105 106 107
M (M)
4 2 2 4
log nHtot (cm3)
1 2 3 4 5 6 7
log T(K)
103 104 105 106 107
M (M)
4 2 2 4
log nHtot (cm3)
6 5 4 3 2 1
log fH
103 104 105 106 107
M (M)
4 2 2 4
log nHtot (cm3)
0.0 0.2 0.4 0.6 0.8 1.0
fH2
103 104 105 106 107
M (M)
4 2 2 4
log nHtot (cm3)
6 5 4 3 2 1
log fH
103 104 105 106 107
M (M)
4 2 2 4
log nHtot (cm3)
1 2 3 4 5 6 7
log T(K)
103 104 105 106 107
M (M)
October 2nd, 2017 University of Malta
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The effect of the interstellar radiation
100 101 102 103
Σgas (M/pc2)
104 103 102 101 100
˙ Σ? (M/yr/kpc2)
G RAD S G RT G RAD T 101 100 101 102 103
ΣH2 (M/pc2)
102 101 100 101 102 103
˙ Σ? (M/Gyr/pc2)
0.1 Gyr 1 Gyr 10 Gyr G RAD S G RT G RAD T
October 2nd, 2017 University of Malta
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What’s next
zfin = 6 Mvir ~ 2x1012 M⦿ —————————— Mgas = ~ 1.5x104 M⦿/part MDM = ~ 8x104 M⦿/part —————————— Ngas = 6.75x107 NDM = 6.75x107 NDM,low = 2.2x107 —————————— 휖gas,min = 40 cpc | 2.5 pc 휖DM = 640 cpc | 40 pc 휖star = 192 cpc | 12 pc 2) Formation of C+ in dwarf galaxies, using a more complete network including C, O an Si. 1)
October 2nd, 2017 University of Malta
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Conclusions
We developed a new model to accurately track H2 in numerical simulations using the package KROME, including photochemistry, SF, SNe, stellar radiation and shielding (gas, dust, H2). We tested the model on an idealised setup of an isolated galaxy with typical properties of z=3 galaxies, assessing the effect of the different processes included.
- We found that the correlation between H2 and SF surface densities can be naturally
reproduced, if we account for all the most important processes and for a self-consistent clumping factor.
- We found that the correlation is also maintained at low H2 surface densities.
- We concluded that an H2-dependent SF prescription is not necessary and also
unmotivated.
October 2nd, 2017 University of Malta
Lupi et al. 2017 (submitted) - soon on ArXiv
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