Dark molecular gas in Pegasus–Pisces

We examine the molecular content of a large region (∼2200 square degrees) in Pegasus–Pisces with an estimated dark molecular gas fraction of 59 per cent. Using the extensive CO(1-0) Southern Galactic hemisphere, high-latitude survey by Magnani et al. (2000), we re-examined the CO-detectable mass estimates for the region. By averaging all the CO spectra in subsections ranging in size from 3° × 3° to 15° × 15°, we decreased the rms of the averaged CO spectra by factors of 3–10, effectively trading spatial resolution for sensitivity. With the new spectra, we are able to make estimates of the CO-detectable mass as a function of sensitivity. Using the optimal estimate, the CO-detectable mass increases from 2200 to 4000 M⊙, thereby decreasing the dark molecular gas fraction in the region to 0.24. CO(1–0) observations with rms values in the 20–30 mK range can nearly double the molecular mass in regions with diffuse and translucent molecular clouds.