2010ApJ...711..399Q

We present the Submillimeter Array (SMA) observations of molecular lines at 330 and 340 GHz toward G19.61 - 0.23. The SMA observations have a spatial resolution of ∼2'' and a bandpass of 2x2 GHz bandwidth. With the SMA data, we have detected 131 molecular transitions. Ninety-four molecular transitions from 17 species and their isotopomers are identified, including complex organic molecules and simple linear molecules. Most of the complex molecules (CH₃OH, ¹³CH₃OH, C₂H₅OH, HCOOCH₃, HNCO, NH₂CHO, CH₃CN, and CH₃CH₂CN) have a sufficient number of transitions in this observation to allow analysis using the rotational temperature diagram method. The results from rotation temperature diagram fitting have shown that the complex nitrogen-bearing molecules have higher rotation temperatures (296-609 K) and lower column densities (6.5x10¹⁵-6.4x10¹⁶/cm2). In contrast, the temperatures and column densities of the complex oxygen-bearing molecules range from 95 to 151 K, and from 1.1x10¹⁶ to 5.2x10¹⁷/cm2, respectively. The H₂ column density is estimated from the submillimeter continuum, and the fractional abundances of various species relative to H₂ are calculated. The oxygen-bearing molecules have higher fractional abundances than those of the nitrogen-bearing molecules. The different gas temperatures and fractional abundances suggest a chemical differentiation between oxygen- and nitrogen-bearing molecules. The images of the spatial distribution of different species have shown that the oxygen-bearing and nitrogen-bearing molecules peak at different positions. Through comparing the rotation temperatures and fractional abundances with the spatial distributions of the molecules, we discuss possible chemical processes for producing the complex molecules, as well as nitrogen and oxygen differentiation in G19.61 - 0.23.