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Herschel-SPIRE Fourier transform spectrometer observations of excited CO and [CI] in the antennae (NGC 4038/39): warm and cold molecular gas

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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 similar to 19"-43") and spectral (1.2 GHz) resolution mapping spectrometer covering a large spectral range (194-671 mu m, 450-1545 GHz). We detect five CO transitions (J = 4-3 to J = 8-7), both [CI] transitions, and the [N I] 205 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 Am. Using the CO and [CI] transitions, we perform both a local thermodynamic equilibrium (LTE) analysis of [CI] 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 similar to 10-30 K) and a warm (T-kin greater than or similar to 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) similar to 5 x 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 alpha(co) similar to 7 M circle dot pc(-2) (K km s(-1))(-1) in the cold component, similar to the value for normal spiral galaxies. We estimate the cooling from H-2, [C II], CO, and [O 1] 63 Am to be similar to 0.01 L circle dot/M circle dot. 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) similar to 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.
Keywords
galaxies: interactions, infrared: galaxies, NGC 4039), galaxies: individual (NGC 4038, ISM: molecules, submillimeter: galaxies, SPECTRAL ENERGY-DISTRIBUTION, STAR-FORMING GALAXIES, INTERSTELLAR-MEDIUM, NEARBY GALAXIES, SUPERNOVA-REMNANTS, CIRCUMNUCLEAR DISK, INFRARED GALAXIES, ARP 220, EMISSION, M82

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Citation

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MLA
Schirm, Maximilien RP, Christine D Wilson, Tara J Parkin, et al. “Herschel-SPIRE Fourier Transform Spectrometer Observations of Excited CO and [CI] in the Antennae (NGC 4038/39): Warm and Cold Molecular Gas.” ASTROPHYSICAL JOURNAL 781.2 (2014): n. pag. Print.
APA
Schirm, M. R., Wilson, C. D., Parkin, T. J., Kamenetzky, J., Glenn, J., Rangwala, N., Spinoglio, L., et al. (2014). Herschel-SPIRE Fourier transform spectrometer observations of excited CO and [CI] in the antennae (NGC 4038/39): warm and cold molecular gas. ASTROPHYSICAL JOURNAL, 781(2).
Chicago author-date
Schirm, Maximilien RP, Christine D Wilson, Tara J Parkin, Julia Kamenetzky, Jason Glenn, Naseem Rangwala, Luigi Spinoglio, et al. 2014. “Herschel-SPIRE Fourier Transform Spectrometer Observations of Excited CO and [CI] in the Antennae (NGC 4038/39): Warm and Cold Molecular Gas.” Astrophysical Journal 781 (2).
Chicago author-date (all authors)
Schirm, Maximilien RP, 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, and Ronin Wu. 2014. “Herschel-SPIRE Fourier Transform Spectrometer Observations of Excited CO and [CI] in the Antennae (NGC 4038/39): Warm and Cold Molecular Gas.” Astrophysical Journal 781 (2).
Vancouver
1.
Schirm MR, Wilson CD, Parkin TJ, Kamenetzky J, Glenn J, Rangwala N, et al. Herschel-SPIRE Fourier transform spectrometer observations of excited CO and [CI] in the antennae (NGC 4038/39): warm and cold molecular gas. ASTROPHYSICAL JOURNAL. 2014;781(2).
IEEE
[1]
M. R. Schirm et al., “Herschel-SPIRE Fourier transform spectrometer observations of excited CO and [CI] in the antennae (NGC 4038/39): warm and cold molecular gas,” ASTROPHYSICAL JOURNAL, vol. 781, no. 2, 2014.
@article{4385142,
  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 similar to 19"-43") and spectral (1.2 GHz) resolution mapping spectrometer covering a large spectral range (194-671 mu m, 450-1545 GHz). We detect five CO transitions (J = 4-3 to J = 8-7), both [CI] transitions, and the [N I] 205 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 Am. Using the CO and [CI] transitions, we perform both a local thermodynamic equilibrium (LTE) analysis of [CI] 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 similar to 10-30 K) and a warm (T-kin greater than or similar to 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) similar to 5 x 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 alpha(co) similar to 7 M circle dot pc(-2) (K km s(-1))(-1) in the cold component, similar to the value for normal spiral galaxies. We estimate the cooling from H-2, [C II], CO, and [O 1] 63 Am to be similar to 0.01 L circle dot/M circle dot. 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) similar to 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.},
  articleno    = {101},
  author       = {Schirm, Maximilien RP and Wilson, Christine D and Parkin, Tara J and Kamenetzky, Julia and Glenn, Jason and Rangwala, Naseem and Spinoglio, Luigi and Pereira-Santaella, Miguel and Baes, Maarten and Barlow, Michael J and Clements, Dave L and Cooray, Asantha and De Looze, Ilse and Karczewski, Oskar Ł and Madden, Suzanne C and Rémy-Ruyer, Aurélie and Wu, Ronin},
  issn         = {0004-637X},
  journal      = {ASTROPHYSICAL JOURNAL},
  keywords     = {galaxies: interactions,infrared: galaxies,NGC 4039),galaxies: individual (NGC 4038,ISM: molecules,submillimeter: galaxies,SPECTRAL ENERGY-DISTRIBUTION,STAR-FORMING GALAXIES,INTERSTELLAR-MEDIUM,NEARBY GALAXIES,SUPERNOVA-REMNANTS,CIRCUMNUCLEAR DISK,INFRARED GALAXIES,ARP 220,EMISSION,M82},
  language     = {eng},
  number       = {2},
  pages        = {24},
  title        = {Herschel-SPIRE Fourier transform spectrometer observations of excited CO and [CI] in the antennae (NGC 4038/39): warm and cold molecular gas},
  url          = {http://dx.doi.org/10.1088/0004-637X/781/2/101},
  volume       = {781},
  year         = {2014},
}

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