Green Bank Telescope observations of interstellar glycolaldehyde: Low-temperature sugar

Interstellar glycolaldehyde (CH2OHCHO) has been detected with the 100 m Green Bank Telescope (GBT) toward the star-forming region Sagittarius B2(N) by means of the 1(10)-1(01), 2(11)-2(02), 3(12)-3(03), and 4(13)-4(04) rotational transitions at 13.48, 15.18, 17.98, and 22.14 GHz, respectively. An analysis of these four high signal-to-noise ratio rotational transitions yields a glycolaldehyde state temperature of similar to8 K. Previously reported emission-line detections of glycolaldehyde with the NRAO 12 m telescope at millimeter wavelengths (71-103 GHz) are characterized by a state temperature of similar to50 K. By comparison, the GBT detections are surprisingly strong and are seen in emission at 13.48 GHz, emission and absorption at 15.18 GHz, and absorption at 17.98 and 22.14 GHz. We attribute the strong absorption observed by the GBT at the higher frequencies to the correspondingly smaller GBT beams coupling better to the continuum source(s) in Sagittarius B2(N). A possible model for the two-temperature regions of glycolaldehyde is discussed.