Schirm, MRP;
Wilson, CD;
Parkin, TJ;
Kamenetzky, J;
Glenn, J;
Rangwala, N;
Spinoglio, L;
... Wu, R; + view all
(2014)
Herschel-SPIRE Fourier Transform Spectrometer observations of excited CO and [C I] in the Antennae (NGC 4038/39): warm and cold molecular gas.
The Astrophysical Journal
, 781
(2)
, Article 101. 10.1088/0004-637X/781/2/101.
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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 ~ 19''-43'') and spectral (~1.2 GHz) resolution mapping spectrometer covering a large spectral range (194-671 μm, 450-1545 GHz). We detect five CO transitions (J = 4-3 to J = 8-7), both [C I] transitions, and the [N II] 205 μm 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 μm. 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 ~ 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 ~ 5 × 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 αCO ~ 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 μm to be ~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 ~ 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.
| Type: | Article |
|---|---|
| Title: | Herschel-SPIRE Fourier Transform Spectrometer observations of excited CO and [C I] in the Antennae (NGC 4038/39): warm and cold molecular gas |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1088/0004-637X/781/2/101 |
| Publisher version: | https://doi.org/10.1088/0004-637X/781/2/101 |
| Language: | English |
| Additional information: | This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions. |
| Keywords: | galaxies: individual (NGC 4038, NGC 4039), galaxies: interactions, infrared: galaxies, ISM: molecules, submillimeter: galaxies |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10093776 |
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