Lecture 23 Flashcards
what do stars form of
cold gas made of mostly Hydrogen and helium, small proportion of metals
what is the interstellar medium made of
Hydrogen, helium, metals, and dust
what temp does gas have to be to fall into a halo
under the virial temperature otherwise it is too hot
what are the coolest regions of gas called in halos
molecular clouds - stars typically form here
what is the kennicutt-schmidt law?
a scaling relation that relates the amount of cold gas in a region to the amount of new star formation
what is stimulated emission
bright stars light up nearby gas
gas absorbs specific wavelengths which bumps up the electrons
electrons fall back down emitting specific wavelengths
what is emission line nebulae
colours around stars caused by stimulated emission
it is from the light within the star interacting with the gas around it
what is the best way to measure galaxy star formation rates
emission lines
what is dust in space
metals that coagulate into molecules, typically carbonaceous or silicate
what is dust destroyed by
high temp - dust smashes and breaks
high uv - photons smash apart the dust
supernova - supersonic shocks that smash dust
dust is fragile !
how is dust created
planetary nebulae - dying stars make metals, making a gentle cooler environment for dust to stick together
supernova - remnants produce dust in a similar way
what is dust reddening
dust scatters UV and blue light
how can we get past dust
near-ir light is not absorbed much
what id dust reprocessing
photos absorbed in the optical and UV are remitted in the mid-far IR so mid-far IR is a tracer of dust
why cant dust survive in ellipticals
little star formation, not much cool gas so it cant survive
what are starburst galaxies
when halos merge, galaxies merge
this causes gas to be driven to the middle and become dense
by the k-s law, dense gas means lots of star formation
what are ultra luminous IR galaxies
dense dust causing most light from the galaxy to come out in IR
why don’t irregulars have much dust
very young so not enough time to build up metals from previous generations of stars
despite cold gas, not much metals, not much dust
IR emission in ellipticals, discs and starbursts and ULIRGS
ellipticals don’t have much, disks have a bit more
starbursts and ULIRGS are extremely bright
