摘要
The H 2 S 2 2, 0 -2 1, 1 and SO 5 5 -4 4 transitions were observed simultaneously toward the starburst galaxy NGC 253 using the Submillimeter Array. Two H 2 S emission peaks are found at positions ∼2″ northeast (30 pc) and ∼5″ southwest (80 pc) from the galactic center, associated with the circumnuclear disk and coinciding with the inner ring structure seen on the SiO map by García-Burillo and coworkers. SO emission is detected, weakly, only toward the northeast, By combining data in the literature, we estimate H 2 S rotational temperatures of 130 K toward the northeast H 2 S peak and 46 K toward the southwest peak and derive H 2 S column densities of ∼3 and ∼1 × 10 15 cm -2 and SO column densities of ∼4 and ≤3 × 10 14 cm -2 toward the northeast and southwest peaks, respectively. The fractional abundances, relative to molecular hydrogen, are f∼ (1-3) × 10 -8 and 4 × 10 -9 for H 2 S and SO, comparable with the values observed in Galactic massive star forming cores. The H 2 S emission is supposed to trace the ongoing star formation through hot core activity, and a rough comparison with the massive star forming region Orion KL indicates that several thousands of Orion KL-like cores may exist toward each of the H 2 S peaks. © 2007. The American Astronomical Society. All rights reserved.