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Title: Herschel-spire Fourier transform spectrometer observations of excited CO and [C I] in the antennae (NGC 4038/39): Warm and cold molecular gas

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 {sub kin} ∼ 10-30 K) and a warm (T {sub kin} ≳ 100 K) component. By comparing the warm gas mass to previouslymore » observed values, we determine a CO abundance in the warm gas of x {sub CO} ∼ 5 × 10{sup –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{sub CO} ∼ 7 M {sub ☉} pc{sup –2} (K km s{sup –1}){sup –1} in the cold component, similar to the value for normal spiral galaxies. We estimate the cooling from H{sub 2}, [C II], CO, and [O I] 63 μm to be ∼0.01 L {sub ☉}/M {sub ☉}. 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 {sub 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.« less
Authors:
; ;  [1] ; ; ;  [2] ; ;  [3] ; ;  [4] ;  [5] ;  [6] ;  [7] ;  [8] ; ; ;  [9]
  1. Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1 (Canada)
  2. Center for Astrophysics and Space Astronomy, 389-UCB, University of Colorado, Boulder, CO 80303 (United States)
  3. Istituto di Astrofisica e Planetologia Spaziali, INAF-IAPS, Via Fosso del Cavaliere 100, I-00133 Roma (Italy)
  4. Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, B-9000 Gent (Belgium)
  5. Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom)
  6. Astrophysics Group, Imperial College, Blackett Laboratory, Prince Consort Road, London SW7 2AZ (United Kingdom)
  7. Department of Physics and Astronomy, University of California, Irvine, CA 92697 (United States)
  8. Department of Physics and Astronomy, University of Sussex, Brighton BN1 9QH (United Kingdom)
  9. CEA, Laboratoire AIM, Irfu/SAp, Orme des Merisiers, F-91191 Gif-sur-Yvette (France)
Publication Date:
OSTI Identifier:
22348100
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 781; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; ANTENNAS; CARBON MONOXIDE; DENSITY; FAR ULTRAVIOLET RADIATION; FOURIER TRANSFORM SPECTROMETERS; GALAXIES; HEAT; HYDROGEN; INTERACTIONS; LTE; LUMINOSITY; MASS; MOLECULES; PERTURBED ANGULAR CORRELATION; RADIANT HEAT TRANSFER; RESOLUTION; STELLAR WINDS; TURBULENT HEATING