Super spirals are the most massive star-forming disk galaxies in the universe ( 42 ; 41 ) .
We measured rotation curves for 23 massive spirals Based on observations made with the Southern African Large Telescope ( SALT ) and find a wide range of fast rotation speeds ( 240-570 km s ^ { -1 } ) , indicating enclosed dynamical masses of 0.6 - 4 \times 10 ^ { 12 } M _ { \odot } .
Super spirals with mass in stars \log M _ { \mathrm { stars } } / M _ { \odot } > 11.5 break from the baryonic Tully-Fisher relation ( BTFR ) established for lower mass galaxies .
The BTFR power-law index breaks from 3.75 \pm 0.11 to 0.25 \pm 0.41 above a rotation speed of \sim 340 km s ^ { -1 } .
Super spirals also have very high specific angular momenta that break from the ( 17 ) relation .
These results indicate that super spirals are undermassive for their dark matter halos , limited to a mass in stars of \log M _ { \mathrm { stars } } / M _ { \odot } < 11.8 .
Most giant elliptical galaxies also obey this fundamental limit , which corresponds to a critical dark halo mass of \log M _ { \mathrm { halo } } / M _ { \odot } \simeq 12.7 .
Once a halo reaches this mass , its gas can no longer cool and collapse in a dynamical time .
Super spirals survive today in halos as massive as \log M _ { \mathrm { halo } } / M _ { \odot } \simeq 13.6 , continuing to form stars from the cold baryons they captured before their halos reached critical mass .
The observed high-mass break in the BTFR is inconsistent with the Modified Newtonian Dynamics ( MOND ) theory ( 2 ) .