19 - Dark Matter Halos

What counters cosmic expansion?

Gravity

Far from a halo, matter moves _____. Near a halo, matter _______ towards the halo.

Apart, collapses

What is the divine line between matter collapsing and moving apart called?

The turnaround radius

If there is more mass, it needs more _______ _________ to hold itself up.

Velocity dispersion

What happens when smaller halos merge in?

They contribute their angular momentum to the main halo, speeding up the spin.

How do you quantify spin?

Spin parameter I measures the amount of rotation support, typically around 3%

Halos are not entirely dispersion-supported; there is a tiny amount of _______ support too.

Rotational

The closer to the middle of a halo you go, the more the ________, so matter is denser.

pressure

Simulations in the 1990s showed that all halos have broadly a similar _______ _____

density profile

A common representation of the scale radius is the __________.

Concentration

A halo with larger mass will have a ____ radius and a ______ concentration

Larger, smaller

The first halos are tiny, formed from tiny CMB __________.

Fluctuations

Halos grow by eating other halos, i.e. _______. This is known as __________ growth.

Merging, hierarchical

What is growth by mergers represented by?

Merger trees

After a smaller halo is merged in, for a while it still retains some identity as its own unit, known as a ________, eventually mixing in with the main halo.

Sub-halo

Based on a merger tree, how do you define the age of a halo?

The time when half its main progenitor mass assembled

Concentration is ______ at lower halo mass. Halos remember the density of the universe when it was formed: Smaller halos formed ______, with higher concentration.

Higher, earlier