Direct estimation of electron density in the Orion Bar PDR from mm-wave carbon recombination lines.

ABSTRACT: A significant fraction of the molecular gas in star-forming regions is irradiated by stellar UV photons. In these environments, the electron density (ne) plays a critical role in the gas dynamics, chemistry, and collisional excitation of certain molecules. We determine ne in the prototypical strongly irradiated photodissociation region (PDR), the Orion Bar, from the detection of new millimeter-wave carbon recombination lines (mmCRLs) and existing far-IR [13Cii] hyperfine line observations. We detect 12 mmCRLs (including α, β, and γ transitions) observed with the IRAM 30m telescope, at ~ 25″ angular resolution, toward the H/H2 dissociation front (DF) of the Bar. We also present a mmCRL emission cut across the PDR. These lines trace the C+/C/CO gas transition layer. As the much lower frequen

SUBMITTER: Cuadrado S 

PROVIDER: S-EPMC6558286 | biostudies-literature | 2019 May

REPOSITORIES: biostudies-literature