THE MULTI-PHASE COLD FOUNTAIN IN M82 REVEALED BY A WIDE, SENSITIVE MAP OF THE MOLECULAR INTERSTELLAR MEDIUM
- Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States)
- Max Planck Institute für Astronomie, Königstuhl 17, D-69117, Heidelberg (Germany)
- Institut d’Astrophysique de Paris, Sorbonne Universités, UPMC (Univ. Paris 06), CNRS (UMR 7095), F-75014 Paris (France)
- Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)
- National Radio Astronomy Observatory, P.O. Box O, 1003 Lopezville Road, Socorro, NM 87801 (United States)
- Max-Planck-Institut für Radioastronomie, Auf dem Hgel 69, D-53121 Bonn (Germany)
- Department of Astronomy, University of Maryland, College Park, MD (United States)
- IRAM, 300 rue de la Piscine, F-38406 St. Martin d’Hères (France)
- Observatoire de Geneve, 1290 Sauverny (Switzerland)
We present a wide area (≈8 × 8 kpc), sensitive map of CO (2–1) emission around the nearby starburst galaxy M82. Molecular gas extends far beyond the stellar disk, including emission associated with the well-known outflow as far as 3 kpc from M82's midplane. Kinematic signatures of the outflow are visible in both the CO and H i emission: both tracers show a minor axis velocity gradient and together they show double peaked profiles, consistent with a hot outflow bounded by a cone made of a mix of atomic and molecular gas. Combining our CO and H i data with observations of the dust continuum, we study the changing properties of the cold outflow as it leaves the disk. While H{sub 2} dominates the ISM near the disk, the dominant phase of the cool medium changes as it leaves the galaxy and becomes mostly atomic after about a kpc. Several arguments suggest that regardless of phase, the mass in the cold outflow does not make it far from the disk; the mass flux through surfaces above the disk appears to decline with a projected scale length of ≈1–2 kpc. The cool material must also end up distributed over a much wider angle than the hot outflow based on the nearly circular isophotes of dust and CO at low intensity and the declining rotation velocities as a function of height from the plane. The minor axis of M82 appears so striking at many wavelengths because the interface between the hot wind cavity and the cool gas produces Hα, hot dust, polycyclic aromatic hydrocarbon emission, and scattered UV light. We also show the level at which a face-on version of M82 would be detectable as an outflow based on unresolved spectroscopy. Finally, we consider multiple constraints on the CO-to-H{sub 2} conversion factor, which must change across the galaxy but appears to be only a factor of ≈2 lower than the Galactic value in the outflow.
- OSTI ID:
- 22521868
- Journal Information:
- Astrophysical Journal, Vol. 814, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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