Lecture 21 Flashcards
relationship between galaxies forming from halos and where halos form from
galaxies form in halos, halos form in the nodes of the cosmic web
what is a galaxy cluster
a very large halo consumes smaller halos
each small halo forms a galaxy
how does gas behave in clusters
since gravity is so strong, the gas is heated to incredible high temperatures and cannot cool
its photons are emitted as x rays
what is the virial temperature
the temperature gas needs to be stable against gravity (hold itself up with kinetic energy)
what are galaxy groups
step down from clusters but contain several Milky Way sized galaxies
groups contain most of the galaxies in the universe
what are field/void galaxies
galaxies with no comparable size neighbours
what is the environment go galaxies connected to
how quickly the node hierarchy assembled of the halo
fast - clusters
what types of galaxies do clusters typically contain and why
more mergers as more galaxies so more big ellipticals
these are oldest galaxies
what types of galaxies do groups typically contain
spirals have mild interactions so modest spirals
middle aged galaxies
what types of galaxies do field galaxies have
very few interactions so small spirals
young galaxies
what types of galaxies are voids
irregular
what is the local group
contains Milky Way and Andromeda
Milky Way has two large-ish satellites - LMC, SMC
some dwarf satellites too
what is the missing satellites problem
LambdaCDM predicts hundreds of small halos around the Milky Way forming tiny disk galaxies
only see a few dozen
solutions to missing satellites problem
- could not have been found (but we have looked hard)
- galaxies don’t form in small halos (SHMR says small halos don’t form galaxies efficiently)
- lambda CDM is wrong
