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Published February 10, 2015 | Published + Submitted
Journal Article Open

ALMA Imaging of HCN, CS, and Dust in Arp 220 and NGC 6240


We report ALMA Band 7 (350 GHz) imaging at 0."4-0."6 resolution and Band 9 (696 GHz) at ~0."25 resolution of the luminous IR galaxies Arp 220 and NGC 6240. The long wavelength dust continuum is used to estimate interstellar medium masses for Arp 220 east and west and NGC 6240 of 1.9, 4.2, and 1.6 × 10^9 M_☉ within radii of 69, 65, and 190 pc. The HCN emission was modeled to derive the emissivity distribution as a function of radius and the kinematics of each nuclear disk, yielding dynamical masses consistent with the masses and sizes derived from the dust emission. In Arp 220, the major dust and gas concentrations are at radii less than 50 pc in both counter-rotating nuclear disks. The thickness of the disks in Arp 220 estimated from the velocity dispersion and rotation velocities are 10-20 pc and the mean gas densities are n_H_2 ~ 10^5 cm^(–3) at R <50 pc. We develop an analytic treatment for the molecular excitation (including photon trapping), yielding volume densities for both the HCN and CS emission with n_(H2) ~ 2 × 10^5 cm^(–3). The agreement of the mean density from the total mass and size with that required for excitation suggests that the volume is essentially filled with dense gas, i.e., it is not cloudy or like swiss cheese.

Additional Information

© 2015 American Astronomical Society. Received 2014 October 2; accepted 2014 December 15; published 2015 February 10. We thank the referee for a very thorough reading of the manuscript. We thank Zara Scoville for proofreading the manuscript. K.S. is supported by the National Radio Astronomy Observatory, which is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This paper makes use of the following ALMA data: ADS/JAO.ALMA 2011.0.00175.S. ALMA is a partnership of ESO (representing its member states), NSF (USA), and NINS (Japan); together with NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ.

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Published - 0004-637X_800_1_70.pdf

Submitted - 1412.5183v1.pdf


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August 22, 2023
August 22, 2023