CO J=1-0 spectroscopy of four submillimeter galaxies with the Zpectrometer on the Green Bank Telescope

TL;DR

This study used the Zpectrometer on the Green Bank Telescope to detect CO J=1-0 lines in three high-redshift submillimeter galaxies, revealing complex interstellar media and implications for molecular mass estimates.

Contribution

First detection of CO J=1-0 in multiple high-redshift SMGs, showing multi-component interstellar media and challenging assumptions in molecular mass calculations.

Findings

CO J=1-0 line is stronger than expected, affecting mass estimates.

Interstellar media in SMGs are multi-component, not single-phase.

Method developed for detecting weak lines in broadband spectra.

Abstract

We report detections of three z ~ 2.5 submillimeter-selected galaxies (SMGs; SMM J14011+0252, SMM J14009+0252, SMM J04431+0210) in the lowest rotational transition of the carbon monoxide molecule (CO J = 1-0) and one nondetection (SMM J04433+0210). For the three galaxies we detected, we find a line-integrated brightness temperature ratio of the J = 3-2 and 1-0 lines of 0.68 +/- 0.08; the 1-0 line is stronger than predicted by the frequent assumption of equal brightnesses in the two lines and by most single-component models. The observed ratio suggests that mass estimates for SMGs based on J = 3-2 observations and J = 1-0 column density or mass conversion factors are low by a factor of 1.5. Comparison of the 1-0 line intensities with intensities of higher-J transitions indicates that single-component models for the interstellar media in SMGs are incomplete. The small dispersion in the ratio, along with published detections of CO lines with J_upper > 3 in most of the sources, indicates that the emission is from multi-component interstellar media with physical structures common to many classes of galaxies. This result tends to rule out the lowest scaling factors between CO luminosity and molecular gas mass, and further increases molecular mass estimates calibrated against observations of galaxies in the local universe. We also describe and demonstrate a statistically sound method for finding weak lines in broadband spectra that will find application in searches for molecular lines from sources at unknown redshifts.