H2 based Star Formation -

Progress Report

with Frazer Pearce, Inti Pelupessy, Padelis Papadopoulos, Paul Torrey

Hanni Lux

Outline | SubGrid ISM

Final Goal:

Run a “more realistic” cosmological simulation of galaxy formation with additional observable predictions

Means:

Use Gadget +SubgridISM

Status:

Testing Implementation + Physical consistency

Why is this interesting?

• Stars form in molecular clouds in the MW/other nearby galaxies (Blitz 1993, Fukui &Kawamura 2010)

• SFR seems to be correlated stronger with the H2 surface density than the HI surface density (Wong & Blitz 2002)

• Jury is still out on whether stars form from H2 or both form under similar conditions

•Many CO/H2 observations to match

SGISM | Model•H2 formation on dust grains

•H2 destruction by UV radiation (self-shielding + dust shielding)

•H2 destruction by collisions in WNM phase

• time-dependent algorithm

• star formation recipe based on H2 fraction + stellar feedback

•Metal + H2 cooling

Pelupessy et al. 2006, 2009

SGISM | Parameters

•H2 formation uncertainties fudge factor

• unknown density profile in molecular clouds

•Ortho-to-Para ratio of hydrogen

SGISM | Parameters

•H2 formation uncertainties fudge factor

• unknown density profile in molecular clouds

•Ortho-to-Para ratio of hydrogen

Do not seem to introduce the biggest uncertainties!

SGISM | Model

Pelupessy et al. 2006, 2009

n, T, Z, ne, dt

SGISM | Temp. Dependence

Pelupessy et al. 2006, 2009

T > T4 = 104K:No molecular hydrogen can exist above thistemperature (Cazaux & Tielens 2004).

T4 ≥ T > Tdes = 3× 103K:H2 destruction through collisions.

Tdes ≥ T > Tform = 103KH2 destruction through external radiation field.

Tform ≥ T :H2 formation in equilibrium with destructionthrough external radiation field.

Subgrid ISM | H2 Fraction

Figure 3: The equilibrium molecular fraction fm in dependence of the gas num-ber density n and the gas temperature T for di!erent parameter sets. Theseplots show the contours corresponding to fm = 0.1, 0.3, 0.6, 0.9, respectively.The plots are created for a formation rate parameter µ = 3.5 and values forthe cloud power-law index !, the metallicity Z the radiation field G0 in unitsof the Draine field and the velocity dispersion "/km/s as denoted in each plot.These plots are analogous to Figure 1 in [8].

6

Cloud Model

Radiation field

Vel. Disp.

Metallicity

fH2 =2nH2

n

Subgrid ISM | H2 Fraction

Figure 3: The equilibrium molecular fraction fm in dependence of the gas num-ber density n and the gas temperature T for di!erent parameter sets. Theseplots show the contours corresponding to fm = 0.1, 0.3, 0.6, 0.9, respectively.The plots are created for a formation rate parameter µ = 3.5 and values forthe cloud power-law index !, the metallicity Z the radiation field G0 in unitsof the Draine field and the velocity dispersion "/km/s as denoted in each plot.These plots are analogous to Figure 1 in [8].

6

Cloud Model

Radiation field

Vel. Disp.

MetallicityMetallicity

fH2 =2nH2

n

SGISM | Metal Cooling

from C, N, O, Ne, Si, Fe

Raga et al. 1997, Silva & Viegas 2001

SGISM | H2 Cooling

LeBourlot et al. (1999)

n = 104cm−3

n = 100cm−3

n = 108cm−3

O/P = 1

fH2 = 0.9

SGISM in Gadget | Status

•H2 formation + destruction

• Primordial Cooling + Heating

•Metal Cooling

•H2 Cooling

•H2 based star formation

• Stellar Feedback

• ...

Pelupessy et al. (2006,2009), Katz et al. (1996), Le Bourlot et al. (1999), Silva & Viegas (2001)

SGISM in Gadget | Status

•H2 formation + destruction

• Primordial Cooling + Heating

•Metal Cooling

•H2 Cooling

•H2 based star formation

• Stellar Feedback

• ...

Pelupessy et al. (2006,2009), Katz et al. (1996), Le Bourlot et al. (1999), Silva & Viegas (2001)

SGISM in Gadget | Status

•H2 formation + destruction

• Primordial Cooling + Heating

•Metal Cooling

•H2 Cooling

•H2 based star formation

• Stellar Feedback

• ...

Pelupessy et al. (2006,2009), Katz et al. (1996), Le Bourlot et al. (1999), Silva & Viegas (2001)

SGISM in Gadget | Status

•H2 formation + destruction

• Primordial Cooling + Heating

•Metal Cooling

•H2 Cooling

•H2 based star formation

• Stellar Feedback

• ...

Pelupessy et al. (2006,2009), Katz et al. (1996), Le Bourlot et al. (1999), Silva & Viegas (2001)

SGISM in Gadget | Status

•H2 formation + destruction

• Primordial Cooling + Heating

•Metal Cooling

•H2 Cooling

•H2 based star formation

• Stellar Feedback

• ...

Pelupessy et al. (2006,2009), Katz et al. (1996), Le Bourlot et al. (1999), Silva & Viegas (2001)

SGISM in Gadget | Status

•H2 formation + destruction

• Primordial Cooling + Heating

•Metal Cooling

•H2 Cooling

•H2 based star formation

• Stellar Feedback

• ...

Pelupessy et al. (2006,2009), Katz et al. (1996), Le Bourlot et al. (1999), Silva & Viegas (2001)

SGISM in Gadget | Status

•H2 formation + destruction

• Primordial Cooling + Heating

•Metal Cooling

•H2 Cooling

•H2 based star formation

• Stellar Feedback

• ...

Pelupessy et al. (2006,2009), Katz et al. (1996), Le Bourlot et al. (1999), Silva & Viegas (2001)

SGISM | Tests

• collapse of a self-gravitating rotating gas sphere

• initially softened NFW profile (e.g. Sijacki et al. 2012)

• N = 104, M = 1012M⊙, Λ = 0.05

SGISM | Tests

SGISM | Tests

Outlook | Tests

•Investigating the effect of resolved/unresolved metallicity

•non-cosmological runs (mergers)

Outlook | Physics

• Low Z, H2 Formation (For Cosmologial Simulations)

•CO Formation/Destruction (Pelupessy et al. 2009)

•Non-Standard SPH (SPHS/ Hopkins 2012)

•Radiative Transfer

•Metal Diffusion?

SGISM | Summary

•H2 formation/destruction + cooling modules work as stand alone versions

• Implementation in Gadget still needs to be smoothed out

•More tests needed!

•More physics needed for consistent treatment!