The first galaxies in the Universe are the building blocks of all observed galaxies .
We present scaling relations for galaxies forming at redshifts z \geq 15 when reionization is just beginning .
We utilize the ‘ ‘ Rarepeak ’ ’ cosmological radiation hydrodynamics simulation that captures the complete star formation history in over 3,300 galaxies , starting with massive Population III stars that form in dark matter halos as small as \sim 10 ^ { 6 } { M _ { \odot } } .
We make various correlations between the bulk halo quantities , such as virial , gas , and stellar masses and metallicities and their respective accretion rates , quantifying a variety of properties of the first galaxies up to halo masses of 10 ^ { 9 } { M _ { \odot } } .
Galaxy formation is not solely relegated to atomic cooling halos with virial temperatures greater than 10 ^ { 4 } \textrm { K } , where we find a dichotomy in galaxy properties between halos above and below this critical mass scale .
Halos below the atomic cooling limit have a stellar mass – halo mass relationship \log M _ { \star } \simeq 3.5 + 1.3 \log ( M _ { vir } / 10 ^ { 7 } { M _ { \odot } } ) .
We find a non-monotonic relationship between metallicity and halo mass for the smallest galaxies .
Their initial star formation events enrich the interstellar medium and subsequent star formation to a median of 10 ^ { -2 } { Z _ { \odot } } and 10 ^ { -1.5 } { Z _ { \odot } } , respectively , in halos of total mass 10 ^ { 7 } { M _ { \odot } } that is then diluted by metal-poor inflows , well beyond Population III pre-enrichment levels of 10 ^ { -3.5 } { Z _ { \odot } } .
The scaling relations presented here can be employed in models of reionization , galaxy formation and chemical evolution in order to consider these galaxies forming prior to reionization .