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We present new observations from Z-Spec, a broadband 185-305 GHzspectrometer, of five sub-millimeter bright lensed sources selected from theHerschel Astrophysical Terahertz Large Area Survey (H-ATLAS) sciencedemonstration phase (SDP) catalog. We construct a redshift finding algorithmusing combinations of the signal-to-noise of all the lines falling in theZ-Spec bandpass to determine redshifts with high confidence, even in caseswhere the signal-to-noise in individual lines is low. We measure the dustcontinuum in all sources and secure CO redshifts for four out of five(z~1.5-3). In one source, SDP.17, we tentatively identify two independentredshifts and a water line, confirmed at z=2.308. Our sources have propertiescharacteristic of dusty starburst galaxies, with magnification-corrected starformation rates of 10^(2-3) M_sun/yr. Lower limits for the dust masses (~a few10^8 M_sun) and spatial extents (~1 kpc equivalent radius) are derived from thecontinuum spectral energy distributions, corresponding to dust temperaturesbetween 54 and 69K. In the LTE approximation, we derive relatively low COexcitation temperatures (< 100 K) and optical depths (tau<1). Performing anon-LTE excitation analysis using RADEX, we find that the CO lines measured byZ-Spec (from J=4->3 to 10->9, depending on the galaxy) localize the bestsolutions to either a high-temperature / low-density region, or alow-temperature / high-density region near the LTE solution, with the opticaldepth varying accordingly. Observations of additional CO lines, CO(1-0) inparticular, are needed to constrain the non-LTE models.

Measurements of CO redshifts with Z-Spec for lensed submillimeter galaxies discovered in the H-ATLAS survey