GBT Zpectrometer CO(1-0) Observations of the Strongly-Lensed Submillimeter Galaxies from the Herschel ATLAS

TL;DR

This study uses the GBT Zpectrometer to measure CO(1-0) redshifts and molecular gas masses of strongly-lensed submillimeter galaxies from Herschel H-ATLAS, confirming their high redshifts and gas content, and comparing their properties to local ULIRGs.

Contribution

First measurements of CO(1-0) redshifts and molecular gas masses for Herschel-selected lensed SMGs using GBT, demonstrating the effectiveness of CO lines for redshift determination.

Findings

CO(1-0) redshifts of z=3.042 and z=2.625 obtained

Molecular gas masses of (1--3)x10^{10} Msun measured

No evidence for enhanced L(IR)/L'(CO) ratios compared to local ULIRGs

Abstract

The Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) has uncovered a population of strongly-lensed submillimeter galaxies (SMGs). The Zpectrometer instrument on the Green Bank Telescope (GBT) was used to measure the redshifts and constrain the masses of the cold molecular gas reservoirs for two candidate high-redshift lensed sources. We derive CO(1-0) redshifts of z=3.042+/-0.001 and z=2.625+/-0.001, and measure molecular gas masses of (1--3)x10^{10}Msun, corrected for lens amplification and assuming a conversion factor of alhpa=0.8 Msun(K km/s pc^2)^{-1}. We find typical L(IR)/L'(CO) ratios of 120+/-40 and 140+/-50 Lsun (K km/s pc^2)^{-1}, which are consistent with those found for local ULIRGs and other high-redshift SMGs. From analysis of published data, we find no evidence for enhanced L(IR)/L'(CO(1-0)) ratios for the SMG population in comparison to local ULIRGs. The GBT results highlight the power of using the CO lines to derive blind redshifts, which is challenging for the SMG population at optical wavelengths given their high obscuration.