TY - JOUR

T1 - Strong Far-ultraviolet Fields Drive the [C II]/Far-infrared Deficit in z ∼ 3 Dusty, Star-forming Galaxies

AU - Rybak, Matus

AU - Calistro Rivera, G.

AU - Hodge, J. A.

AU - Smail, Ian

AU - Walter, F.

AU - van der Werf, P.

AU - da Cunha, E.

AU - Chen, Chian-Chou

AU - Dannerbauer, H.

AU - Ivison, R. J.

AU - Karim, A.

AU - Simpson, J. M.

AU - Swinbank, A. M.

AU - Wardlow, J. L.

PY - 2019/5/8

Y1 - 2019/5/8

N2 - We present 0.″15 (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 ≃2 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.

AB - We present 0.″15 (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 ≃2 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.

KW - galaxies: high-redshift

KW - galaxies: star formation

KW - submillimeter: galaxies

U2 - 10.3847/1538-4357/ab0e0f

DO - 10.3847/1538-4357/ab0e0f

M3 - Journal article

VL - 876

SP - 112

JO - The Astrophysical Journal

JF - The Astrophysical Journal

SN - 0004-637X

IS - 2

ER -