Herschel SPIRE-FTS Observations of Excited CO and [CI] in the Antennae (NGC 4038/39): Warm and Cold Molecular Gas

Maximilien R. P. Schirm; Christine D. Wilson; Tara J. Parkin; Julia Kamenetzky; Jason Glenn; Naseem Rangwala; Luigi Spinoglio; Miguel Pereira-Santaella; Maarten Baes; Michael J. Barlow; Dave L. Clements; Asantha Cooray; Ilse De Looze; Oskar Ł. Karczewski; Suzanne C. Madden; Aurélie Rémy-Ruyer; Ronin Wu

doi:10.1088/0004-637X/781/2/101

paper

Herschel SPIRE-FTS Observations of Excited CO and [CI] in the Antennae (NGC 4038/39): Warm and Cold Molecular Gas

arXiv:1312.2522 · doi:10.1088/0004-637X/781/2/101

Abstract

We present Herschel SPIRE-FTS observations of the Antennae (NGC 4038/39), a well studied, nearby ( $22$ Mpc) ongoing merger between two gas rich spiral galaxies. We detect 5 CO transitions ( $J = 4 - 3$ to $J = 8 - 7$ ), both [CI] transitions and the [NII] $205 μ m$ 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 PACS observations of [CII] and [OI] $63 μ m$ . Using the CO and [CI] transitions, we perform both a LTE analysis of [CI], and a non-LTE radiative transfer analysis of CO and [CI] 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 ( $T_{k in} \sim 10 - 30$ K) and a warm ( $T_{k in} ≳ 100$ K) component. By comparing the warm gas mass to previously observed values, we determine a CO abundance in the warm gas of $x_{C O} \sim 5 \times 1 0^{- 5}$ . 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 $α_{C O} \sim 7 M_{⊙} p c^{- 2} (K k m s^{- 1})^{- 1}$ in the cold component, similar to the value for normal spiral galaxies. We estimate the cooling from H $_{2}$ , [CII], CO and [OI] $63 μ m$ to be $\sim 0.01 L_{⊙} / M_{⊙}$ . We compare PDR 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 $G_{0} \sim 1000$ . 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.

50 pages, 15 figures, 8 tables, Accepted for publication in The Astrophysical Journal

Herschel SPIRE-FTS Observations of Excited CO and [CI] in the Antennae (NGC 4038/39): Warm and Cold Molecular Gas

Abstract

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