The Dynamical Masses, Densities, And Star Formation Scaling Relations Of Ly Alpha Galaxies

We present the first dynamical mass measurements for Ly alpha galaxies at high redshift, based on velocity dispersion measurements from rest-frame optical emission lines and size measurements from Hubble Space Telescope imaging, for nine galaxies drawn from four surveys. We use these measurements to study Ly alpha galaxies in the context of galaxy scaling relations. The resulting dynamical masses range from 109 to 10(10) M-circle dot. We also fit stellar population models to our sample and use them to place the Ly alpha sample on a stellar mass versus line width relation. The Ly alpha galaxies generally follow the same scaling relation as star-forming galaxies at lower redshift, although, lower stellar mass fits are also acceptable in similar to 1/3 of the Ly alpha galaxies. Using the dynamical masses as an upper limit on gas mass, we show that Ly alpha galaxies have unusually active star formation for their gas mass surface density. This behavior is consistent with what is observed in starburst galaxies, despite the typically smaller masses and sizes of the Ly alpha galaxy population. Finally, we examine the mass densities of these galaxies and show that their future evolution likely requires dissipational ("wet") merging. In short, we find that Ly alpha galaxies are low-mass cousins of larger starbursts.