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Strong far-ultraviolet fields drive the [C ii]/far-infrared deficit in z ∼ 3 dusty, star-forming galaxies.

Rybak, Matus and Rivera, G. Calistro and Hodge, J. A. and Smail, Ian and Walter, F. and van der Werf, P. and da Cunha, E. and Chen, Chian-Chou and Dannerbauer, H. and Ivison, R. J. and Karim, A. and Simpson, J. M. and Swinbank, A. M. and Wardlow, J. L. (2019) 'Strong far-ultraviolet fields drive the [C ii]/far-infrared deficit in z ∼ 3 dusty, star-forming galaxies.', Astrophysical journal., 876 (2). p. 112.


We present 0farcs15 (1 kpc) resolution ALMA observations of the [C ii] 157.74 μm line and rest-frame 160 μm continuum emission in two z ~ 3 dusty, star-forming galaxies—ALESS 49.1 and ALESS 57.1, combined with resolved CO (3–2) observations. In both sources, the [C ii] surface brightness distribution is dominated by a compact core ≤1 kpc in radius, a factor of 2–3 smaller than the extent of the CO (3–2) emission. In ALESS 49.1, we find an additional extended (8 kpc radius), low surface brightness [C ii] component. Based on an analysis of mock ALMA observations, the [C ii] and 160 μm continuum surface brightness distributions are inconsistent with a single-Gaussian surface brightness distribution with the same size as the CO (3–2) emission. The [C ii] rotation curves flatten at sime2 kpc radius, suggesting that the kinematics of the central regions are dominated by a baryonic disk. Both galaxies exhibit a strong [C ii]/far-IR (FIR) deficit on 1 kpc scales, with FIR surface brightness to [C ii]/FIR slope steeper than in local star-forming galaxies. A comparison of the [C ii]/CO (3–2) observations with photodissociation region models suggests a strong far-UV (FUV) radiation field (G 0 ~ 104) and high gas density (n(H) ~ 104–105 cm−3) in the central regions of ALESS 49.1 and ALESS 57.1. The most direct interpretation of the pronounced [C ii]/FIR deficit is a thermal saturation of the C+ fine-structure levels at temperatures ≥500 K, driven by the strong FUV field.

Item Type:Article
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Publisher statement:© 2019. The American Astronomical Society. All rights reserved.
Date accepted:05 March 2019
Date deposited:30 May 2019
Date of first online publication:08 May 2019
Date first made open access:30 May 2019

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