Large‐Scale Structure of the Molecular Gas in Taurus Revealed by High Linear Dynamic Range Spectral Line Mapping

We report the results of a 100 deg 2 survey of the Taurus molecular cloud region in 12 CO and 13 CO J = 1→ 0. The image of the cloud in each velocity channel includes ≃3 × 10 6 Nyquist-sampled pixels on a 20 ” grid. The high sensitivity and large spatial dynamic range of the maps reveal a very complex, highly structured cloud morphology, including filaments, cavities, and rings. The axes of the striations seen in the 12 CO emission from relatively diffuse gas are aligned with the direction of the magnetic field. We have developed a statistical method for analyzing the pixels in which 12 CO but not 13 CO is detected, which allows us to determine the CO column in the diffuse portion of the cloud, as well as in the denser regions in which we detect both isotopologues. Using a column-density-dependent model for the CO fractional abundance, we derive the mass of the region mapped to be 2.4 × 10 4 M ☉ , more than twice as large as would be obtained using a canonical fixed fractional abundance of 13 CO, and a factor of 3 greater than would be obtained considering only the high column density regions. We determine that half the mass of the cloud is in regions having column density below 2.1 × 10 21 cm −2 . The distribution of young stars in the region covered is highly nonuniform, with the probability of finding a star in a pixel with a specified column density rising sharply for N (H 2 ) = 6 × 10 21 cm −2 . We determine a relatively low star formation efficiency (mass of young stars/mass of molecular gas), between 0.3% and 1.2%, and an average star formation rate during the past 3 Myr of 8 × 10 −5 stars yr −1 .