2007ApJ...661L.135M

The H₂ S 2_2, 0_–21, 1_and SO 5₅-4₄transitions were observed simultaneously toward the starburst galaxy NGC 253 using the Submillimeter Array. Two H₂ 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 H₂ S rotational temperatures of 130 K toward the northeast H₂S peak and 46 K toward the southwest peak and derive H₂ S column densities of ∼3 and ∼1x10¹⁵/cm2 and SO column densities of ∼4 and ≤3x10¹⁴/cm2 toward the northeast and southwest peaks, respectively. The fractional abundances, relative to molecular hydrogen, are f∼1-3x10^–8 and 4x10^–9 for H₂ S and SO, comparable with the values observed in Galactic massive star forming cores. The H₂ 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 H₂ S peaks.