Relativistic ideal Fermi gas at zero temperature and preferred frame

We discuss the limit $T\to 0$ of the relativistic ideal Fermi gas of luxons (particles moving with the speed of light) and tachyons (hypothetical particles faster than light) based on observations of our recent paper: K. Kowalski, J. Rembieliński, and K. A. Smoliński, Phys. Rev. D 76, 045018 (2007). For bradyons this limit is in fact the nonrelativistic one and therefore it is not studied herein.