By R. Dave, slides here.
- 4 phases of baryons:
- diffuse
- unbound shock-heated
- virial shock-heated (condensed)
- cool halo gas (condensed)
- low mas haloes cannot keep their gas
- how gas gets into galaxies:
- hot mode (shock heating at virial radius, cooling onto disk. slower, limited by cooling time, more spherical)
- cool mode: more rapid, line emission cooled, filamentary: cold streams (dominant: cold accretion dominates globally, mergers are a small contribution to gas supply: SF is supply-limited)
- mergers: DM grows by mergers (mass fn is steep), mergers contribute little to gas supply
- mass dependence of accretion mode: large halos: hot mode, small halos: cold mode, separation at roughly ~10^{11.5} M_{\odot}, with metal cooling -- 10^{12} M_{\odot} -- connection with galaxy bimodality
- shock stability: shocks form up from a certain mass, that's why cold mode dominates (virial shocks cannot form)
- simulations
- accretion w/out feedback overpredicts cold baryon mass (overcooling): conversion efficiency peaks at 10 ^{12}
- red and dead: AGN feedback as the power source, blue: SNe, YSOs
- abundance matching: equate nr density of haloes and galaxies with a given mass -- halo occupation distribution -- galaxies and satellites. Procedure assigns galaxies to haloes, matching halo masses to stellar masses, Behroozi +13 -- peak of conversion efficiency constant at all redshifts.
- galaxies are gas processing factories: raw materials from IGM (infall rate due to gravity)
- not all infall material ends up in the galaxy -- some gas is prevented from getting into the galaxy, outflow of hot and polluted gas from SF regions (just like in a factory), some outflow material is recaptured -- infall metallicity (\alpha_z in the diagram)
- resulting SF: mass balance: infall = formed stars + Outflow + gas reservoir change
- equilibrium condition: reservoir gas is constant over time (from hydro and obs, not true for dwarfs, just for L_{\star}) --> high z galaxies have higher ISM gas fractions
- Inflow: primordial and recycled gas: recycling metallicity vs. SN ejecta metallicity
- SFR: set by 3 baryon cycling parameters:
- feedback preventing parameter (inflow)
- outflow mass loading factor (outflow)
- recycled wind metallicity ratio
- SFH does not depend on (it's expressed in correlations):
- SF law
- merger history
- environment or clustering
- morphology
- gas content
- MS of galaxy evolution: SFR vs. M_{\star}:
- relation should be close to linear, D. Elbaz
- SFR should grow with z rapidly --> feeding rate change
- feedback parameters:
- quenching at high mass (AGN?)
- gravitational heating transition to hot mode (\zeta_{grav}, RD 2012) -- power law all the way to high masses, weak dependence on z
- wind heating suppress accretion
- specific SFR: feedback effects
- gas metallicity relation, its evolution -- gas phase metallicities
- gas content, M_{gas} -- cold gas in the ISM:
- H_2 gas fraction ~= t_{dep} \cdot sSFR (how much gas is in the ISM that waits to become stars)
- depletion time t_{dep}
- t_{dep}: depends on Schmidt law, Kennicutt relation
- SF law sets t_{dep}, which sets f_{gas} ~ t_{dep}
- the role of merging: second order effect (like environment), sets scatter (e.g. M_{star}-Z relation)
- first order: smooth accretion
- second order: stochasticity: clumps (mergers) --> lower Z, higher SFR (signals recent accretion event) --> high star formation points lie below MZ relation
- dilution time -- explains scatter
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