A NEW SUBMILLIMETER GRATING SPECTROMETER

We have detected emission in the J = 6 → 5 transition (λ = 453 µm) of the carbon monoxide isotopologue 13CO from the starburst nucleus of the nearby galaxy NGC 253. This is the first extragalactic detection of this transition, which traces the warm, dense molecular gas found in regions of massive star forma-tion. An excitation analysis of the CO line strengths measured here and ob-tained from the literature finds that ≈ 35 % − 60 % of the molecular gas mass (MH2 ≈ 2.9 × 107 M⊙) in the nuclear region is both warm (T ∼ 110 K) and dense (nH2 ∼ 104 cm−3). We find that the gas is most likely heated either by an elevated density of cosmic rays, or by the dissipation of supersonic turbulence. As both of these heat sources are the result of stellar feedback within the starburst, our analysis suggests that the starburst may be self-limiting. We also present the detection of emission in the 2P3/2 → 2P1/2 transition (λ = 158 µm) of ionized carbon from MIPS J142824.0+352619, an extremely lu-minous star-forming galaxy at z = 1.325. We combine this measurement with existing observations of the far-infrared continuum and CO emission to esti