Poster Presentation

Relationship between [CI] and CO inside molecular clouds probed by absorption line observations with ALMA

Author(s): Yusuke Miyamoto (Fukui University of Technology)

Presenter: Yusuke Miyamoto (Fukui University of Technology)

In the photodissociation region (PDR) model, which is the basis for the structural description of molecular clouds, neutral atoms are expected to be distributed in layers on the surface of molecular clouds due to dissociation by interstellar UV radiation. On the other hand, recent observations of molecular clouds in the Galaxy and extra galaxies have revealed cases in which the distribution of neutral atomic carbon ([CI]) and carbon monoxide (CO) is consistent. The Clumpy-PDR model has been proposed as a model to explain these results. When molecular clouds have inhomogeneous internal structures, e.g., dense clumps exist in diffuse molecular clouds, UV radiation can penetrate into the molecular clouds and dissociate molecular gases, which explains the agreement between [CI] and CO distributions at the molecular cloud scale. This model has been attempted to be verified by observations of [CI] emission lines at high spatial resolution (several 100 to several 1000 AU) towards molecular clouds in the Galaxy, but this has not yet been proven. To confirm the existence of high-density clumps (≤ 100 au) deep inside molecular clouds and to compare [CI] and CO on this spatial scale would be useful. Therefore, we measured the molecular clouds in the Galaxy as absorption lines by observing quasars behind the Galaxy. When high-density clumps in molecular clouds are observed with high spatial resolution, absorption lines with velocity widths corresponding to the size of the clumps are expected to be detected. Comparison of CO and [CI] spectral profiles also allow us to infer their spatial relationship. In this talk, I will present the results of 12CO, 13CO, and [CI] with ALMA for two quasars behind the Galaxy.