Redshift distribution of faint submm galaxies inferred from their radio-to-submm spectral index

Utilizing the radio-FIR correlation obeyed by all star forming galaxies, we have recently proposed radio-to-submm spectral index as a redshift indicator for dusty star forming galaxies at high redshifts (see Carilli & Yun 1999). A large scatter in the relation limits the utility of this technique, and only a gross redshift estimation is possible for any individual source. A statistical inference on the redshift distribution is more secure, and we derive a conservative lower limit to the median redshift of 2.0 for the published sample of faint submm sources. Modeling observed spectral energy distribution (SED) in terms of star formation rate offers a useful insight into the nature of the scatter. Rapid determination of detailed radio-to-IR SEDs should become possible using ALMA and next generation radio telescopes (e.g. expanded VLA), and the SED modeling may be used to derive more reliable redshifts.