Lecture 24

Question 1

what can we hypothesise about high-redshift galaxies

Answer 1

fewer and smaller - not enough time to grow hierarchically
forming stars - denser universe, radiative cooling easier
younger - universe isn’t old enough

Question 2

is early galaxies being fewer and smaller true or false

Answer 2

true - data confirms this

Question 3

is younger galaxies being bluer star forming and younger true or false

Answer 3

true
star forming fraction increases towards higher redshifts
bluer once redshift is accounted for

Question 4

what does JWST’s increased sensitivity show?

Answer 4

many previous irregulars and ellipticals actually have faint spiral arms

Question 5

what happens at a low redshift with mergers

Answer 5

spirals are destroyed, irregulars formed, these become ellipticals

if gas rich, disk regrows

Question 6

what is the madau plot and what does it show

Answer 6

a graph of the cosmic SFR density as a function of redshift

star formation rate increases to a peak then drops off at Z = 2

shows early universe forms stars faster

Question 7

explain the rise in the madau plot

Answer 7

bigger galaxies, more gravity, more gas falling in, more SF

Question 8

what are the possibilities for the drop at Z=2 in madau plot

Answer 8

universe less dense, cooling less efficient, gas accretion slower so less SF but happening earlier so why z=2?

universe stars to accelerate, stuff moves apart faster, harder to get infall, less SF but acceleration dominates at z <~1

massive galaxies start to form into ellipticals and quench

Question 9

what redshift do we observe massive quenched galaxies becoming increasingly common

Answer 9

Z~2-3

Question 10

what is the main sequence

Answer 10

star forming galaxies

Question 11

what is the rough story of milky way

Answer 11

started out small
grew along main sequence, growing in mass and SFR
at z~2. resembled a spiral galaxy
early old stars formed the bulge which is redder, bluer disk is where star formation occurs
today it is star forming spiral
in 5 Gyr, will merge with Andromeda and form an elliptical

Question 12

what is cosmic dawn

Answer 12

first stars and galaxies appearing (roughly first billion years)

need high sensitivity and IR to detect these

Question 13

what is reionization

Answer 13

universe went from being ionised to neutral (opaque to transparent)

when first stars formed, lots of UV light was put out that recognised the universe taking about a billion years

Question 14

current improvements due to JWST

Answer 14

detecting galaxies in epoch of reionization

galaxies seem to form earlier and brighter than we thought

not yet saw first stars