MOLECULAR CLOUDS IN THE NORTH AMERICAN AND PELICAN NEBULAE: STRUCTURES

Abstract

We present observations of 4.25 square degree area toward the North American and Pelican Nebulae in the $J = 1-0$ transitions of $^{12}$CO, $^{13}$CO, and C$^{18}$O. Three molecules show different emission area with their own distinct structures. These different density tracers reveal several dense clouds with surface density over 500 $M_\odot$ pc$^{-2}$ and a mean H$_2$ column density of 5.8, 3.4, and 11.9$\times10^{21}$ cm$^{-2}$ for $^{12}$CO, $^{13}$CO, and C$^{18}$O, respectively. We obtain a total mass of $5.4\times10^4 M_\odot$ ($^{12}$CO), $2.0\times10^4 M_\odot$ ($^{13}$CO), and $6.1\times10^3 M_\odot$ (C$^{18}$O) in the complex. The distribution of excitation temperature shows two phase of gas: cold gas ($\sim$10 K) spreads across the whole cloud; warm gas ($>$20 K) outlines the edge of cloud heated by the W80 H II region. The kinetic structure of the cloud indicates an expanding shell surrounding the ionized gas produced by the H II region. There are six discernible regions in the cloud including the Gulf of Mexico, Caribbean Islands and Sea, Pelican's Beak, Hat, and Neck. The areas of $^{13}$CO emission range within 2-10 pc$^2$ with mass of (1-5)$\times10^3 M_\odot$ and line width of a few km s$^{-1}$. The different line properties and signs of star forming activity indicate they are in different evolutionary stages. Four filamentary structures with complicated velocity features are detected along the dark lane in LDN 935. Furthermore, a total of 611 molecular clumps within the $^{13}$CO tracing cloud are identified using the ClumpFind algorithm. The properties of the clumps suggest most of the clumps are gravitationally bound and at an early stage of evolution with cold and dense molecular gas.