Galaxy Formation: high-z observations


(Notes borrowed from ASTR222)


Complications:

Cosmological effects distort our view of high redshift galaxies:
We use imperfect clocks to judge evolution:

High redshift galaxies are intrinsically different from those around us today -- they are younger. Think of comparing a massive galaxy nearby to a massive galaxy in the early universe:



Reminder: Connection between redshift and age (for H0=72, OmegaM=0.25, OmegaL=0.75):




The Hubble Ultradeep Field

Field of view: 202x202 arcseconds (1/100th the area of the full moon)

    Half scale
    Full resolution




Looking across space and back through time/redshift: how do we assess redshifts for galaxies?

(courtesy Mauro Giavalisco)



How well do they compare? Not bad, if you can tolerate some catastrophically bad outliers:



(from Brian Mobasher)



So we can look at the deep imaging, estimate redshifts (then confirm spectroscopically for better accuracy when necessary) and look at samples of galaxies at different redshifts. From Conselice, ARAA, 2014:
High redshift galaxies often look smaller, lumpier, and bluer than galaxies at intermediate and low redshift.


What about morphology? Look at massive galaxies first (again from
Conselice, ARAA, 2014). The mix of types appears to change with redshift -- Peculiar objects and disky things first, spheroidal types later. But this is almost certainly very dependent on environment and galaxy mass!