lit: Where do the dwarf galaxies go?

I've just attended a colloquium by J. Navarro of the NFW fame, which was really related to my current reading list. I'm writing an introductory chapter on hierarchical galaxy assembly for my thesis at the moment.
One unsolved problem of LCDM cosmology is the apparent lack of dwarf galaxies: simulations and statistical frameworks (such as EPS) predict that we should see a large number (hundreds) of dwarf galaxies around each bright galaxy such as the Milky Way, but we only know of a dozen. Same with Andromeda.
J. Navarro also showed some puzzling properties of local dwarfs, for example, the fact that their star formation histories are wildly different. Some formed all their gas 10 or so Gyr ago, some had a starburst recently, and some have double-peaked SFH's. He presented the work of his student which could explain it: the CLUES simulation shows that a combination of interaction with the collapsing cosmic web, mergers of dwarfs and reionisation stripping can in principle explain this. Some dwarfs lost their gas simply because they moved too fast through the cosmic web. The remainders of such galaxies may be just too faint for us to see.

Jerusalem WS lecture notes: 16. Signatures of Inflows and Outflows

By R. Dave, slides here.

• metals in diffuse IGM -- outflows!
• at high z, SF can't keep up with inflow: the gas accumulation phase: gas can even turn into molecular phase, but due to low efficiency it won't all be processed into stars (equilibrium breaks down), RD 2012
• eta scaling ~ M_{halo} ^{-1/3} -- z_{equil} ~ 5 for massive galaxies
• equilibrium model code at http://ursa.as.arizona.edu/~/rad/work/equil.c
• 'thesis back in the stone age'
• constraining outflow parameters: direct observation and direct modelling are challenging
• direct observation of preventive feedback:
  • mass in CGM: gas in absorption, X-ray emission, soft X-ray bg: COS (Cosmic Origins Spectrograph): OVI high ionisation line, 2 components: photo- and collisional excitation: SF galaxies are probing 300 000 K gas: http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=49663, Anderson 2012
  • direct observations of ejective feedback: outflowing ISM lines: LBG tomography
  • direct observations of wind recycling: _metallicity_ of inflowing gas. Disk outskirts: \alpha_z ~ 0.3
• indirect constraints:
  • counting statistics are not as good as scaling relations
  • galaxies to 0th order are a 1-parameter family (stellar or halo mass) --> good scaling parameters
  • conversion efficiency peaks at 10^{12} M_{\odot}
  • if you don't have winds, you have overcooling problems
  • cosmic SFR efficiency: SFR vs. Halo mass infall rate: a simple combination of model parameters (Behroozi et al), simulations are hard
  • SFR vs. M_{\odot}: galaxy MS is the parameter to compare SF galaxies across redshifts, not SFR -- present starbursts and past normal SF galaxies have identical SFRs
  • MS evolution is currently difficult to model
  • SFR -- metallicity relation
  • M_{star} -- feedback relation
  • M_{star} function -- Baldry 2008 simulations -- reproduces the lower mass GSMF well, arbitrary quenching at logM > 11, governed by differential recycling which flattens the relation at intermediate masses --> inflection
  • gas fractions and X_{co}
• DLAs: kinematics favor ejection, not prevention, CDM has many low-mass halos, if they have many HI, too many narrow DLAs result

Jerusalem WS lecture notes: 13. Galaxy Formation with Inflows and Outflows

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