Gas and metal flows around galaxies in FIRE simulations Du an Kere - - PowerPoint PPT Presentation

Gas and metal flows around galaxies in FIRE simulations

Dušan Kereš

UC San Diego

What Matters Around Galaxies Durham, June 20, 2017

with Sasha Muratov, Bili Dong and the FIRE collaboration

(C.-A Faucher Giguere, P. Hopkins, C. Hummels, N. Murray, E. Quataert, D. Angles-Alcazar, Z. Haffen, T. K. Chan, X. Ma et al.)

FIRE Project

• FIRE resolves ~giant molecular clouds in a multi-phase ISM (m_g~102-104Msun, 1-20pc

in dense ISM): enables local SF and spatial and time correlation of stellar feedback.

• Includes feedback processes from young stars: photo-ionized HII regions, stellar winds,

photoelectric heating, radiation pressure and finally SN energy and momentum.

• No hydro decoupling, no cooling prevention!
• Momentum is crucial: thermal energy cools out, but momentum remains. We carefully

account for the radial momentum generated in the S-T phase of the SNe.

50 kpc scale, ~MW mass at z=0 magenta-cold, green-warm, red-hot gas

Star formation driven outflows

• FIRE reproduces M*-Mh and mass-metallicity relations: success owes to ejection of

metal enriched gas from galaxies.

• Star formation in FIRE is bursty! Bursts drive wind episodes that eject gas out of

galaxies and create cycle of infall, star formation and outflows.

Muratov, Keres et al. 2015

• utflows

infall

~1011Msun halo (z=2)

Lack of low redshift outflows

• Star formation is more continuous at low redshift, no outflows at 0.25Rvir (only local

fountains): enables formation of thin disks!

• Key requirement to form late type disky galaxies.

Muratov, Keres et al. 2015

How much material is expelled?

Muratov, Keres+ 2015

• Mass loading in inner halo (shell at 0.25Rvir) decreases with stellar mass; << 1 in Milky

Way-mass halos at z=0.

z~3 z~1 z~0.25

slope ~ -0.35

Metallicity of the outflows

• Ejected gas has metallicity similar to the ISM (slightly higher at high-z and slightly

lower at low-z and low masses).

• Outflows at Rvir have lower metallicity: entrainment of lower metallicity halos gas,

especially at z<~2. The bulk of ejected metals remains in halos and recycles back

• nto galaxies.

Metal outflows

Muratov, DK et al. 2017

z~3 z~1 z~0.25

• z=2: halos loose about half of the metals and only a small fraction is locked in stars!
• z=0: stellar metal fraction overtakes CGM in ~MW mass galaxies. Halos (except smallest

dwarfs) keep most of the metals, higher fraction than retained baryons.

• The amount of metals in the CGM of L* galaxies broadly agrees with observations (Bouche

+2007, Peeples+14). Obs. estimates are uncertain and simulation statistics are poor.

• More detailed comparisons are needed: e.g. absorption lines.

z=2 z=0

Muratov, Keres et al. 2017

Preliminary: EWs at z~2 for Mh~10^12Msun (e-mail me for details/ figures).

Conclusions

• Stellar feedback in FIRE produces galactic outflows that lower galaxy masses and

eject material into the CGM and IGM.

• Outflows are bursty at low masses and high-z, weak in L* galaxies at low-z.
• Most of the metals produced by galaxies stay within virial radius.
• Detailed studies are needed for proper comparison with observations: important

to have good statistics and/or to capture time evolution of the halo absorbers.

• Halo gas is much calmer at low redshift (talks by C. Hummels and N. Murray

talks) but shows a strong dependence on resolution.