@article{discovery10093776, volume = {781}, title = {Herschel-SPIRE Fourier Transform Spectrometer observations of excited CO and [C I] in the Antennae (NGC 4038/39): warm and cold molecular gas}, journal = {The Astrophysical Journal}, number = {2}, year = {2014}, month = {February}, note = {This version is the version of record. For information on re-use, please refer to the publisher's terms and conditions.}, abstract = {We present Herschel Spectral and Photometric Imaging Receiver (SPIRE) Fourier Transform Spectrometer (FTS) observations of the Antennae (NGC 4038/39), a well-studied, nearby (22 Mpc), ongoing merger between two gas-rich spiral galaxies. The SPIRE-FTS is a low spatial ( FWHM {\texttt{\char126}} 19''-43'') and spectral ({\texttt{\char126}}1.2 GHz) resolution mapping spectrometer covering a large spectral range (194-671 {\ensuremath{\mu}}m, 450-1545 GHz). We detect five CO transitions (J = 4-3 to J = 8-7), both [C I] transitions, and the [N II] 205 {\ensuremath{\mu}}m transition across the entire system, which we supplement with ground-based observations of the CO J = 1-0, J = 2-1, and J = 3-2 transitions and Herschel Photodetecting Array Camera and Spectrometer (PACS) observations of [C II] and [O I] 63 {\ensuremath{\mu}}m. Using the CO and [C I] transitions, we perform both a local thermodynamic equilibrium (LTE) analysis of [C I] and a non-LTE radiative transfer analysis of CO and [C I] using the radiative transfer code RADEX along with a Bayesian likelihood analysis. We find that there are two components to the molecular gas: a cold (T kin {\texttt{\char126}} 10-30 K) and a warm (T kin gsim 100 K) component. By comparing the warm gas mass to previously observed values, we determine a CO abundance in the warm gas of x CO {\texttt{\char126}} 5 {$\times$} 10-5. If the CO abundance is the same in the warm and cold gas phases, this abundance corresponds to a CO J = 1-0 luminosity-to-mass conversion factor of {\ensuremath{\alpha}}CO {\texttt{\char126}} 7 M ? pc-2 (K km s-1)-1 in the cold component, similar to the value for normal spiral galaxies. We estimate the cooling from H2, [C II], CO, and [O I] 63 {\ensuremath{\mu}}m to be {\texttt{\char126}}0.01 L ?/M ?. We compare photon-dominated region models to the ratio of the flux of various CO transitions, along with the ratio of the CO flux to the far-infrared flux in NGC 4038, NGC 4039, and the overlap region. We find that the densities recovered from our non-LTE analysis are consistent with a background far-ultraviolet field of strength G 0 {\texttt{\char126}} 1000. Finally, we find that a combination of turbulent heating, due to the ongoing merger, and supernova and stellar winds are sufficient to heat the molecular gas.}, author = {Schirm, MRP and Wilson, CD and Parkin, TJ and Kamenetzky, J and Glenn, J and Rangwala, N and Spinoglio, L and Pereira-Santaella, M and Baes, M and Barlow, MJ and Clements, DL and Cooray, A and De Looze, I and Karczewski, OL and Madden, SC and R{\'e}my-Ruyer, A and Wu, R}, url = {https://doi.org/10.1088/0004-637X/781/2/101}, keywords = {galaxies: individual (NGC 4038, NGC 4039), galaxies: interactions, infrared: galaxies, ISM: molecules, submillimeter: galaxies} }