Lecture 19 Flashcards
what is the turnaround radius in dark matter halos
the line between where matter moves towards the halo and spreads apart.
different from virial radius
infall region is between virial radius and turnaround radius
what does halos being triaxial mean
they connect to the surrounding large scale structure which reflects the triaxality of the initial density perturbations
what is halo spin
as halos merge in, they contribute their angular momentum to the main halo
it is a random process so all halos the average is 0 but any given halo will have spin
how is halo spin quantified
the parameter measures the amount of rotational support
halos are not entirely dispersion-supported, small amount of rotational support too which is crucial for forming disk galaxies
what is the density profile of a dark matter halo
lower you go, more pressure so matter is more dense towards the middle
what parameters fully define a dark matter halo
mass of the halo, virial radius of the halo, halo spin parameter, halo concentration
mass, radius and Hal concentration are related
how do dark matter halos grow via mergers
first halos are small formed from CMB fluctuations
halos grow by attracting matter around them, much of this is in even smaller halos
so they merge - hierarchical growth
what is growth of halos represented by
a merger tree
what is a sub-halo
for a small period of time when a smaller halo merges in, it retains some identity as its own unit before mixing with main halo
how can you define the age of a halo
based on a merger tree, can define the age as the time when half its main mass assembled
halo concentration vs mass
concentration is higher at lower halo mass, halos remember the same density of the universe when it formed
