Radio–to–Far‐Infrared Spectral Energy Distribution and Photometric Redshifts for Dusty Starburst Galaxies

As a logical next step in improving the radio-to-submm spectral index as aredshift indicator (Carilli & Yun 1999), we have investigated a technique ofusing the entire radio-to-FIR spectral energy distribution (SED) for derivingphotometric redshifts for dusty starburst galaxies at high redshift. A dustystarburst SED template is developed from theoretical understanding on variousemission mechanisms related to massive star formation process, and the templateparameters are selected by examining the observed properties of 23 IR selectedstarburst galaxies: $T_d=58$ K, $\beta=1.35$, and $f_{nth}=1$. The majorimprovement in using this template SED for deriving photometric redshifts isthe significant reduction in redshift uncertainty over the spectral indextechnique, particularly at higher redshifts. Intrinsic dispersion in the radioand FIR SEDs as well as absolute calibration and measurement errors contributeto the overall uncertainty of the technique. The derived photometric redshiftsfor five submm galaxies with known redshifts agree well with theirspectroscopic redshifts within the estimated uncertainty. Photometric redshiftsfor seven submm galaxies without known spectroscopic redshifts (HDF850.1,CUDSS14.1, Lockman850.1, SMM J00266+1708, SMM J09429+4658, SMM J14009+0252,FIRBACK J1608+5418) are derived.Comment: 29 pages with 7 embedded figures and 2 tables. Latex using aastex. To appear in the March 20, 2002 issue (v568) of The Astrophysical Journa