Lecture 27 Flashcards
what is the interstellar medium
gas inside galaxies
what is the circum galactic medium
gas outside galaxies but in the halo
what is the intergalactic medium
gas outside halos
where are baryons in galaxies
mostly in the gas outside galaxies
what is the baryon cycle
inflows from the halo and surrounding filaments, outflows driven by supernovae, recycling of outflow material that rains back in
what is the temperature of deep space and what heats it
very hot
falling onto cosmic web, uv light from galaxies, uv and x rays from Black holes
why do big halos have a hot CGM and smaller ones have a cooler one
big halos have higher velocity dispersion so stronger shocks thus more heating
big halos are fluffier(lower concentration) so less dense so less cooling
what is the virial radius to do with gas
where infalling gas will smash into a wall of stable gas and shock heat
what is the cooling radius to do with gas
where cooling time becomes fast enough to cool gas and fall to the centre
what happens if virial radius > cooling radius
infalling gas will shock heat first then cool near centre
called hot mode accretion
what happens if cooling radius > virial radius
infalling gas cools so quickly that the virial shock doesnt happen
gas freely streams into the centre
called cold mode
is cold mode or hot mode accretion more efficient and why
cold mode is more efficient
allows free streaming to the middle, ignoring virial radius.
why is hot mode accretion inefficient
requires gas to shock, heat up and then cool stalling the inflow
where does cold mode occur
early epochs when universe is denser and cooling is faster
in smaller halos where concentration is higher
what does cool CGM mean
gas cannot support itself again gravity so there is fast cold mode accretion so it is a star forming galaxy
what does a hot cgm mean
gas holds itself up against gravity
slow hot mode accretion
not many new stars forming
thus red and dead
how can we view the CGM with x-rays
hot gas shines with x rays
only happens in massive halos
current sensitivities of telescopes mean cant even see groups well
how can we view the cgm with absorption
absorption lines are formed from light being scattered when quasars behind a galaxy shine through the gas in specific wavelengths
what can we tell from absorption lines with the CGM
how much cgm there is and what is it is made of
