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