Jerusalem WS lecture notes: 14. Observed galaxies from high to low redshift

By Simon Lilly. Slides here.

• individual & population observations
• evolving population: looks simple
• tracers at EM spectrum
• small FOVs of high-z surveys
• young stars: star formation | old stars: stellar mass
• relative sizes of HST surveys
• cosmic variance in high-z surveys -- zCOSMOS is completely dominated by LSS, related to CF
• larger fields: cosmic variance becomes larger relative to Poisson variance: 10% for COSMOS field
• CV fundamental limitation of high-z statistics
• beam sizes are non-negligible, sensitivity is limited by confusion noise
• lensing bias: amplification, esp. faint sources: change LFs
• the success of photo z's (R = 5 'spectroscopy'):
  • empirical approaches
  • template fitting approaches
  • quite good agreement with spectro z's: why do they work? galaxies occupy a small section of parameter space [eigenspectra]
  • spectroscopic surveys: Baldry picture, density vs. area: SDSS-like survey is impossible in high z
  • sample selection
  • sedfitting.org
  • H-R diagram: cool & dim | hot & dim | cool & bright | hot & bright
  • SFR estimates:
    • UV luminosity is best at high z
    • reddening can be estimated from the UV spectrum shape: it does not depend on the IMF, however, mass does, because it is dominated by low mass stars
    • dust absorption: UV is strongly absorbed by dust, estimation from re-radiated emission at IR
    • other UV proxies: H\alpha, [OII] 3727, radio continuum [empirical!], soft X-ray luminosity -- derived at local z
  • how do we define stellar mass?
  • how do we estimate stellar mass?
    • NIR is dominated by RGs, not tracing stellar mass as such. If SFR is constant, it will be dominated by younger populations. If SFR rises with time, SED becomes dominated by younger stars even in NIR.
    • SED fitting output depends on assumed SFR history, exponentially decaying SFR is not valid for higher redshifts, Lee et al, 2010, ApJ: stellar masses are the most robust, then Zs, ages.
  • FMR -- fundamental metallicity relation, Yates et al., 2 methods of SDSS Z estimation
  • sizes, structures and morphologies:
    • ZEST: introduced ellipticity, allows selecting spirals: we can now do automated morph classification
  • environment:
    • http://www.astro.phys.ethz.ch/ZENS/
    • overdensity field in high z Universe
  • halo masses aredifficult to get for lower mass haloes (M < 10^{14})
  • galaxy mergers, see Lotz 2011:
    • a key quantity: for a given galaxy, what part of the stars was brought by mergers, what part formed in situ?
    • observational bias when visually looking for disturbed objects
    • pairs of objects
  • gas content: limited information at high z
  • gas inflows, gas outflows:
    • spectra stacking -- very high S/N spectra of galaxy population
  • incomplete observations:
    • high z gas
    • DM haloes
    • systematic uncertainties in many key quantities: SFRs, M_{st}, Zs, etc.