TY  - JOUR
TI  - Herschel-SPIRE Fourier Transform Spectrometer observations of excited CO and [C I] in the Antennae (NGC 4038/39): warm and cold molecular gas
IS  - 2
ID  - discovery10093776
N1  - This version is the version of record. For information on re-use, please refer to the publisher?s terms and conditions.
Y1  - 2014/02/01/
JF  - The Astrophysical Journal
N2  - 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 ?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 ?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 ?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 ~ 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 ?CO ~ 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 ?m 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.
KW  - galaxies: individual (NGC 4038
KW  -  NGC 4039)
KW  -  galaxies: interactions
KW  -  infrared: galaxies
KW  -  ISM: molecules
KW  -  submillimeter: galaxies
VL  - 781
UR  - https://doi.org/10.1088/0004-637X/781/2/101
A1  - Schirm, MRP
A1  - Wilson, CD
A1  - Parkin, TJ
A1  - Kamenetzky, J
A1  - Glenn, J
A1  - Rangwala, N
A1  - Spinoglio, L
A1  - Pereira-Santaella, M
A1  - Baes, M
A1  - Barlow, MJ
A1  - Clements, DL
A1  - Cooray, A
A1  - De Looze, I
A1  - Karczewski, OL
A1  - Madden, SC
A1  - Rémy-Ruyer, A
A1  - Wu, R
AV  - public
ER  -