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
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