Dense Molecular Gas Tracers in the Outflow of the Starburst Galaxy NGC 253
- Max Planck Institute für Astronomie, Königstuhl 17, D-69117, Heidelberg (Germany)
- Department of Astronomy, Laboratory for Millimeter-wave Astronomy, and Joint Space Institute, University of Maryland, College Park, Maryland 20742 (United States)
- Department of Astronomy, Ohio State University, 100 W 18th Avenue, Columbus, OH 43210 (United States)
- Leiden Observatory, Niels Bohrweg 2, 2333 CA Leiden (Netherlands)
- National Radio Astronomy Observatory, P.O. Box O, 1003 Lopezville Road, Socorro, New Mexico 87801 (United States)
- Department of Astrophysical Sciences, Princeton University, Princeton, New Jersey 08544 (United States)
- Department of Physics, University of Alberta, Edmonton, AB (Canada)
- Astronomy Department, California Institute of Technology, MC105-24, Pasadena, California 91125 (United States)
- Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, Bonn (Germany)
- European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching (Germany)
We present a detailed study of a molecular outflow feature in the nearby starburst galaxy NGC 253 using ALMA. We find that this feature is clearly associated with the edge of NGC 253's prominent ionized outflow, has a projected length of ∼300 pc, with a width of ∼50 pc, and a velocity dispersion of ∼40 km s{sup −1}, which is consistent with an ejection from the disk about 1 Myr ago. The kinematics of the molecular gas in this feature can be interpreted (albeit not uniquely) as accelerating at a rate of 1 km s{sup −1} pc{sup −1}. In this scenario, the gas is approaching an escape velocity at the last measured point. Strikingly, bright tracers of dense molecular gas (HCN, CN, HCO{sup +}, CS) are also detected in the molecular outflow: we measure an HCN(1–0)/CO(1–0) line ratio of ∼1/10 in the outflow, similar to that in the central starburst region of NGC 253 and other starburst galaxies. By contrast, the HCN/CO line ratio in the NGC 253 disk is significantly lower (∼1/30), similar to other nearby galaxy disks. This strongly suggests that the streamer gas originates from the starburst, and that its physical state does not change significantly over timescales of ∼1 Myr during its entrainment in the outflow. Simple calculations indicate that radiation pressure is not the main mechanism for driving the outflow. The presence of such dense material in molecular outflows needs to be accounted for in simulations of galactic outflows.
- OSTI ID:
- 22869462
- Journal Information:
- Astrophysical Journal, Vol. 835, 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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