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: 15. Star-Forming Galaxies

By R. Genzel, slides here

• ways to look back in time:
  • look-back imaging surveys
  • local stellar archaeology
  • detailed, resolved in situ observations
  • pathologies: Hanny's Voorwerp: radiation echo --> timescales of AGN evolution
• SF in MW:
  • shielded regions, pressure comparable to diffuse ISM, density far above MW mean
  • highly structured, velocity dispersion ~5 km/s (supersonic motions), increases with scale
  • unstable to fragmentation
  • in large scales -- virialised, in small scales -- not --> inefficient SF:
  • MW SFR ~ 3 M_{\odot}/yr
  • Krumholz 2005
  • gas depletion time way smaller than Hubble time -- why stars are still forming: MHD pressure (Alfven) prevents collapse, GMCs are magnetically supercritical, but highly supersonic --> theory and observations tend to support the second explanation
• SF occurs in clusters (70-90%, Lada & Lada 1993), super star clusters with M ~ 10^6 M_{\odot} -- from the collapse of the whole MC
• SF tracers: Kennicutt 1998
  • H\alpha: traces Lyman continuum, issues w/ extinction correction
  • UV continuum: IR fine structure lines, C+ --> easily collisionally excited, in areas that are exposed to UV, OI line
  • mid and far IR: calorimetric method: UV heats dust, reprocessing: FIR is currently the best, esp. due to Herschel
  • radio: FIR-radio relation, works if there is no AGN, evolutionary changes
  • SFH uncertainties: SF tracers are no better than 0.3 dex
• pictures of extinction:
  • 'screen' of dust and gas surrounding SF region
  • 'mixed' -- dust and stars are mixed, high and low exctinction regions: you can observe short and high wavelengths together, Calzetti 2000
• dust extinction: 'greyer' -- less dependent on wavelength
• mass tracers (see the slides):
  • SED fitting: live stellar mass
  • rotcurves: dynamical mass: HI not detectable beyond z = 0.1-0.2 until at least SKA
  • velocity dispersion
  • CO -- variation of X
  • lensing
  • submm dust luminosity (ALMA)
  • uncertain up to at least factor of 2: SFH, IMF, extinction, spatial distribution, kinematics, conversion factors
• gas-SF formation:
  • K-S relation (empirical, simple physical motivation (see slides)), Kennicutt & Evans 2012 review
  • conversion factor: MW factor not appropriate for metal poor galaxies
  • classic papers on SF: 'very good papers were written beyond our event horizon': Kenicutt 1983: infall required for SF over cosmic time
  • spatially resolved SF relation: KS law between H_2 and SFR is more linear -- can we ignore HI?
  • HCN traces very dense regions
  • detection thresholds: stellar surface density
  • KS relation breaks down in scales < 500 pc -- CO and H\alpha are not correlated, due to local evolutionary effects: larger areas are necessary to 'smear out'
  • 'J. Gunn in suit'
• VLT: very thin, large mirror supported by adaptive optics pads
• LBT: thin faceplate on light honeycomb ceramic structure
• Concepts for > 20 m telescopes:
  • aplanatic Gregorian optics
  • 30 m telescope (TMT), EELT (10" FoV, 5 mirrors)
• JWST: 6m, 'Keck in space'
• AO:
  • wavefront sensor
  • deformable mirror
  • guide star | artificial guide stars
  • feedback w/ computer
• IFUs: KMOS
• mm interferometry of cold gas:
  • IRAM Plateau de Bure -- exploration of molecular gas in high redshift
  • ALMA: 0.005" resolution, R = 30 000000

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

Jerusalem WS lecture notes: 11. The physics of stellar feedback

By M. Krumholz, the slides.

• 'conservative weed'
• Bate 2009 simulation -- SC formation. SF too efficient and fast -- SF efficiency close to 100%
• what inhibits SF? feedback:
• hot gas or photons push material away from the star, kinetic energy in the material shell = star energy output | radius set by momentum conservation (energy or momentum driven cases, radiation or winds). Mass in the shell way larger than the wind mass
• feedback budgets:
  • Q -- radiant energy, wind energy, number of ionising photons
  • IMF-averaged production rate: luminosity per unit mass (~M/L ratio)
  • lifetime-weighted production rate -- energy out of unit mass (e.g. ergs/g)
  • stochastic IMF sampling in dwarfs -- SLUG code
  • galactic wind: at least as much mass as went into stars
  • what feedbacks are interesting? those that can cause velocities higher than escape velocities --> lower limt
  • losses: gravity, collisions (loss of momentum)
• ISM feedback taxonomy:
  • ionising radiation: not important for galactic winds formation (sound speed ~10 km/s, so can influence in smaller MCs, Krumholz 2006, 2009, Dale 2012), probably the most important SF regulator today
  • radiation pressure (photon momentum, Thompson scattering) -- ~200 km/s -- cannot be responsible for galactic winds, unless radiation enhancing fraction f_{trap} >> 1. Can be important for subgalactic objects, dwarf galaxies, can blow up gas clouds.
  • the important question: what is the f_{trap}?:
  • 30 Dor: dust grain temperature can help infer the IR radiation field, Lopez 2011
  • simulations: 2D, high resoluton: RT instability -- similar to oil floating on water, right panel: no gravity, 2 different optical depths[surface densities]: RP may affect sub-galactic objects, but cannot produce galactic winds, Krumholz & Thompson 2013
  • stellar winds: Solar wind is a wimpy old thing, O stars. Momentum driven
  • 30 Dor -- most massive binary star system, each ~83 M_{\odot}, still on the MS
  • supernovae: energy budget in stars of 8-10 M_{\odot}
    • N_{SN}/M = 0.01 M_{odot}
    • less energy and momentum than radiation feedback
    • more energy, less momentum than winds
    • SN are most important because they are much closer to energy conserving feedback -- large velocities, post-schock ejecta temperatures are ~10^{10} K --> cooling time is ~ 60 Myr, whereas time required to escape the galaxy is << 1 Myr, so gas cannot cool
    • Sedov-Taylor similarity solution -- first developed for nuclear tests, open literature only in 1995 --> energy of Trinity blast from Time pictures (R_blast as a fn of time, Sedov), http://www.seas.harvard.edu/brenner/taylor/handouts/bomb/node1.html
    • trapping factor ~30-40, momentum goes up by this factor during the energy conserving phase, density dependent: SNe explode in low density environments due to star radiation --> f_{trap} is elevated
    • SNs can dominate momentum budget --> proper simulation should take other feedbacks into accounts
  • metallicity feedback
  • metallicity changes SF law (makes difference in dwarfs, high z galaxies) --> metallicity regulated SF (Kuhlen 2012 simulation), interactions wih other feedbacks

Jerusalem WS lecture notes: 09. the IMF and the SFR

By M. Krumholz, slides here. I especially liked Mark's lectures, because he wades into murky, difficult topics of the ISM physics that many researchers like to leave out and assume something.

• THE 2 problems
• IMF:
  • determines stellar feedback (more at top-heavy IMF, etc), abundances, stellar masses
  • Observations:
  • Bastian 2010 -- MW MF plot http://arxiv.org/abs/1001.2965 -- universal IMF in different regions
  • Why a typical star is a few 10ths M_{\odot}? Insensitive to SF environment, metallicity, dwarf/spiral galaxy type
  • Andersen 2009: IMF in MCs (brightest HII region in the Local Group). Sabbi 2008: in SMC (0.2 Z_{\odot})
  • Variation in cDs? van Dokkum & Conroy 2010 (unresolved stars, red & dead galaxies, stars formed at z = 2) -- http://www.nature.com/nature/journal/v468/n7326/abs/nature09578.html: "The direct detection of the light of low-mass stars implies that they are very abundant in elliptical galaxies, making up over 80% of the total number of stars and contributing more than 60% of the total stellar mass. We infer that the IMF in massive star-forming galaxies in the early Universe produced many more low-mass stars than the IMF in the Milky Way disk, and was probably slightly steeper than the Salpeter form in the mass range 0.1M_{\odot} to 1M_{\odot}"
  • Peak location: non-isothermality is required, comes either from:
  • galactic properties, e.g. Hopkins 2012
  • local non-isothermality approximation:
  • isothermality broken by star formation: accreting star is brighter than non-accreting star --> Krumholz 2012: the characteristic mass is set by deviation from isothermality due to SF, the characteristic mass (peak location) depends on pressure of the core (lower mass at higher p). Pressure is set by balance vs. gravity (surface density)
  • Slope: universal, probably due to turbulence
• SFR:
  • bathtub model (gas in, gas out) when t_{SF} << t_H
  • Correlation b/ween molecular gas SD and SF on galactic scales
  • sub-galactic scales: cloud mass vs. no of YSOs, IR luminosity vs. amount of gas (Wu 2005)
  • Galaxy metallicity dependence
  • phase dependence
  • SFR is a function of Toomre Q in galaxy. Dobbs 2011 simulation: self-regulation
  • Top-down model is not sufficient
  • Bottom-up model: what matters is the small scales (local SF law)
  • Why is \epsilon_{eff} (gas conversion to stars ratio) so low, ~1%? Federrath & Klessen 2012 --> few % efficiency for turbulent, virialised objects.
  • l_s -- sound length, size scaling
  • metallicity-phase dependence:
  • why most of the gas is atomic? Dissociation by UV, except in areas where UV is shielded by dust or H_2, 'magic number' -- surface density that shields, ~10M_{\odot}/pc^2
  • why SF follows H_2? Photons that are responsible for dissociation of H_2, are the same that heat the gas, so if the gas is shielded, it cools --> H_2
  • extragalactic phase dependence (SMC has a different SF law because of different metallicity). SF is not only self-regulating process, it depends on global galaxy properties

Jerusalem WS lecture notes: 04. Physics of Star-Forming Clouds

By Mark Krumholz, 'the only obstacle between you and the exciting opportunity to combine drinking with jet lag'. Here are the slides.
Observations:

• SF gas is cold: observations in radio, mm, far-IR
• Diffuse gas: emission lines, dust
• SF ISM is mostly molecular
• H_2: proof that nature has a cruel sense of humour:
  no electronic excitation in cold gas, vibration: mid-IR energy, too high. Rotations: H2 has no dipole mode, no J1 -> J0 transitions, the lowest transition is J2 --> J0. J2 state -- 511 K off ground: no H2 molecules emission.
• CO: proof that astronomers are stubborn bastards:
  
  • If density is high, radiation doesn't change energy distribution (Boltzmann, collisions). Else: way fewer excited molecules than excpected, because collisions don't happen often.
  • Brightness temperature
  • Integrated CO intensity is measure of velocity dispersion (=total gravitating mass), if T = const.
  • Intensity --> directly tells the column density (\Sigma) of CO and H2
  • Motion in gas: bulk, non-thermal, highly supersonic
• Gas properties:
  • cold (10K, 100K in starbursts): adiabatic compression, viscous dissipation, EUV ionisation/FUV photoelectric heating, CR/X ray heating, cooling processes: adiabatic expansion, lines. Dynamical timescales. CRs and X rays can penetrate high columns.
  • Isothermal gas -- efficient cooling if the gas is compressed. Equilibrium T ~ 10K, hard to change. CR -- main source of heating.
  • dense (n > 100cm^{-3})
  • very supersonic: magnetic forces are important, extremely turbulent (Re ~ 10^9).
  • linewidth-size relation (\sigma ~ size of the region), power spectrum
  • VT: thermal motion/thermal pressure prevent collapse, Bonnor-Ebert mass: for a given pressure, there is a maximum mass that can be stable against collapse.
  • for GMCs: M_{BE} ~= 10^7 M_{\odot}: that's why stars form in MCs.