The Plateau de Bure + 30 m arcsecond whirlpool survey reveals a thick disk of diffuse molecular gas in the M51 galaxy
- Institut de Radioastronomie Millimétrique, 300 Rue de la Piscine, F-38406 Saint Martin d'Hères (France)
- Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany)
- National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States)
- Observatorio Astronómico Nacional-OAN, Observatorio de Madrid Alfonso XII, 3, E-28014 Madrid (Spain)
- Instituto Radioastronomía Milimétrica, Avenida Divina Pastora 7, Nucleo Central, E-18012 Granada (Spain)
- School of Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom)
We present the data of the Plateau de Bure Arcsecond Whirlpool Survey, a high spatial and spectral resolution {sup 12}CO (1-0) line survey of the inner ∼10 × 6 kpc of the M51 system, and the first wide-field imaging of molecular gas in a star-forming spiral galaxy with resolution matched to the typical size of giant molecular clouds (40 pc). We describe the observation, reduction, and combination of the Plateau de Bure Interferometer (PdBI) and IRAM-30 m 'short spacing' data. The final data cube attains 1.''1 resolution over the ∼270'' × 170'' field of view, with sensitivity to all spatial scales from the combination of PdBI and IRAM-30 m data, and a brightness sensitivity of 0.4 K (1σ) in each 5 km s{sup –1}-wide channel map. We find a CO luminosity of 9 × 10{sup 8} K km s{sup –1} pc{sup 2}, corresponding to a molecular gas mass of 4 × 10{sup 9} M {sub ☉} for a standard CO-to-H{sub 2} conversion factor. Unexpectedly, we find that a large fraction of this emission, (50 ± 10)%, arises mostly from spatial scales larger than 36'' ≅ 1.3 kpc. Through a series of tests, we demonstrate that this extended emission does not result from a processing artifact. We discuss its origin in light of the stellar component, the {sup 12}CO/{sup 13}CO ratio, and the difference between the kinematics and structure of the PdBI-only and hybrid synthesis (PdBI + IRAM-30 m) images. The extended emission is consistent with a thick, diffuse disk of molecular gas with a typical scale height of ∼200 pc, substructured in unresolved filaments that fill ∼0.1% of the volume.
- OSTI ID:
- 22348513
- Journal Information:
- Astrophysical Journal, Vol. 779, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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