Lecture 30 Flashcards
what causes the cosmic web
gravitational instability
ellipsoidal collapse forms sheets which form filaments which form nodes leaving voids
denser regions have larger fluctuations so collapse quicker
all stages present at any given time
how are redshift surveys mapped as 3D
map 2d in RA and DEC to get distance from redshift
why is distance approximate in redshift surveys
peculiar velocities
how is redshift actually measured
from emission lines or absorption lines from galaxies
cosmic webs effect on cosmological parameters
cosmic web pattern constrains cosmological parameters
what does the correlation function do
measures how clustered galaxies are
how to do a cosmological simulation
start with “particles in a box” with tiny mass fluctuations like the CMB
compute forces, advance velocity, position for small timestamp, repeats until today
soften gravity, set a dynamic range : L/epsilon
set delta t to not be too jumpy
add gas, complex but doable
compare results to known date
what is the endpoint of collapse in dark matter halos
triaxial halo supported by velocity dispersion
why do dark matter halos rotate
due to uneven pull of nearby mass
what are dark matter halos defined by
mass, velocity, dispersion, spin, concentration
what are dark matter halos density like
they have a self similar density profile (NFW), denser in the middle
how do dark matter halos grow and assemble
big halos eat smaller sub halos, big halos assemble late when universe is less dense
how do spiral galaxies form
baryons lose energy and fall into dark matter halos via radiative cooling
cooling ~ density^2 so stronger towards middle of halo
angular momentum is conserved as rotation disk
size of disk is set by the initial spin parameter of the halo
spiral arms are density waves orbiting distinctly from gas and stars
how are other galaxies formed from spirals
spirals merge, orbits random, elliptical galaxy is formed
Hubble sequence
ellipticals - red and dead , spirals - blue and star forming , irregulars - mergers and starbursts
what are the 4 galaxy environments
clusters, groups, field, voids
what is gas in clusters and groups heated to
virial temperature
when do most massive halos form
earliest - biggest and oldest galaxies
where are ellipticals typically and why
dense regions as there are more mergers
what makes up the local group
Milky Way, Andromeda, satellites
what is the missing satellite problem
too many DM sub halos vs satellites, potentially purely cold DM is wrong
explain massive stars (>8M)
live fast (<30mil yr) , burn bright, emit energetic bluer light, die explosively in supernova
they are rare but one massive star can outshine hundreds of low mass stars
explain galaxy colours based on stars and galaxy mass to light
if it is blue, has formed stars recently, most mass is in the lower mass stars but most of the light comes form higher mass stars
what do we expect galaxies and see them to be at earlier times
younger, smaller, more star forming, bluer, more irregular
what is the madau plot
cosmic star formation density history - shows rise then fall
what is the fall in madau plot dye to
increase in large quenched galaxies
what is cosmic dawn
first galaxies form, IGM reionizes
from lambda CDM model and cooling, what do we expect the %mass of any halo to be in stars
10%
what is peak efficiency from observation of baryons
ADD INFO Slide 14
what is feedback
energy that prevents cooling(preventative) and expels cold gas (ejective)
when must feedback be stronger
high and low halo masses
what happens with supernova feedback when a massive star goes supernovae
releases a significant amount of energy 10^51J, that can boil gas out of galaxies
what is supernova feedback particularly effective for
starburst galaxies, smaller galaxies, higher redshift galaxies
what does supernovae feedback explain about low mass halos converting baryons to stars
explains why they are so inefficient
how is supernovae feedback detected
high vel emission or absorption
how do supernovae effect elements
create and disperse heavy elements
where are most of the cosmic baryons contained
IGM - intergalactic medium that is outside halos
where can gas reside in space
inside galaxies (ISM), within the galaxies halo (CGM) or outside of halos (IGM)
what is baryon cycling
gas inflows and outflows going through the cgm
do small halos have hot or cold cgm
cold
do large halos have hot or cold cgm
hot
how is hot cgm saw?
x rays
how is cold cgm saw?
absorption lines
what is the event horizon (Schwarzschild radius)
the point at which matter cannot escape a black hole
how do black holes grow?
massive star seeds via an accretion disk which is limited by the Eddington rate
what forms does the accretion disk release energy in?
winds - driven by radiation pressure
jets - driven by magnetic fields
how did early BHs differ from newer ones
they must’ve either exceeded Eddington rate or came from a different “seed”
AGN feedback vs SNe strength
AGN can way exceed SNe
give info on SMHB’s locations and masses
all sizeable galaxies have central SMBHs and the SMBH’s mass is proportional to the galaxies bulge mass
relationship between mergers and bulgers and SMBH
mergers co-grow bulges with SMBHs, merger to starburst to quasar to elliptical
how does the quasar phase effect star formation
it quenches it temporarily, need to keep CGM hot with jets to quench it fully
AGN feedback process for quenching star formation
merger grows large BH in elliptical, jets from ellipticals BH keep CGM hot, eventually galaxy is starved of gas
SHMR when agn feedback in play
halo mass grows but solar mass doesnt
ellipticals typical environment, size, colour, star formation rate, ISM gas temp, dust?, black hole size? AGN feedback type?
environment: clusters
size: massive
colour: red
star formation rate: low
ISM gas temp: mostly hot
Dust? very little
CGM temp:hot
black hole size?: large
AGN feedback type:jets
spirals typical environment, size, colour, star formation rate, ISM gas temp, dust?, black hole size? AGN feedback type?
environment: groups
size: modest
colour: red+blue
star formation rate: moderate
ISM gas temp: mostly cold
Dust? significant
CGM temp: cool
black hole size?: medium
AGN feedback type:winds
merging irr typical environment, size, colour, star formation rate, ISM gas temp, dust?, black hole size? AGN feedback type?
environment: groups
size: modest
colour: IR
star formation rate: rapid
ISM gas temp: cold
Dust? lots
CGM temp:mixed
black hole size?: growing
AGN feedback type:jets + winds
environment: clusters
size: massive
colour: red
star formation rate: low
ISM gas temp: mostly hot
Dust? very little
CGM temp:hot
black hole size?: large
AGN feedback type:jets
