Strong Far-ultraviolet Fields Drive the [C ii]/Far-infrared Deficit in z ∼ 3 Dusty, Star-forming Galaxies

Rybak, Matus; Rivera, G. Calistro; Hodge, J.A.; Smail, Ian; Walter, F.; van der Werf, P.; da Cunha, E.; Chen, Chian-Chou; Dannerbauer, H.; Ivison, R.J.; Karim, A.; Simpson, J.M.; Swinbank, A.M.; Wardlow, J.L.

Abstract

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.

Citation

Rybak, M., Rivera, G. C., Hodge, J., Smail, I., Walter, F., van der Werf, P., da Cunha, E., Chen, C.-C., Dannerbauer, H., Ivison, R., Karim, A., Simpson, J., Swinbank, A., & Wardlow, J. (2019). Strong Far-ultraviolet Fields Drive the [C ii]/Far-infrared Deficit in z ∼ 3 Dusty, Star-forming Galaxies. Astrophysical Journal, 876(2), Article 112. https://doi.org/10.3847/1538-4357/ab0e0f

• Journal Article Type: Article
• Acceptance Date: Mar 5, 2019
• Online Publication Date: May 8, 2019
• Publication Date: May 10, 2019
• Deposit Date: May 29, 2019
• Publicly Available Date: May 30, 2019
• Journal: Astrophysical Journal
• Print ISSN: 0004-637X
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 876
• Issue: 2
• Article Number: 112
• DOI: https://doi.org/10.3847/1538-4357/ab0e0f
• Public URL: https://durham-repository.worktribe.com/output/1329889