The [C II]/[N II] ratio in 3 < z < 6 sub-millimetre galaxies from the South Pole Telescope survey

• Published in: Monthly Notices of the Royal Astronomical Society
• Main Authors: Cunningham, D. J. M., Chapman, S. C., Aravena, M., De Breuck, C., Bethermin, M., Chen, Chian-Chou, Dong, Chenxing, Gonzalez, A. H., Greve, T. R., Litke, K. C., Ma, J., Malkan, M., Marrone, D. P., Miller, T., Phadke, K. A., Reuter, C., Rotermund, K., Spilker, J. S., Stark, A. A., Strandet, M., Vieira, J. D., Weiss, A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2020
• Subjects: galaxies: evolution; galaxies: high-redshift; galaxies: statistics; submillimetre: galaxies; submillimetre: ISM; STAR-FORMING GALAXIES; DEEP FIELD-SOUTH; REDSHIFT SURVEY; NUMBER COUNTS; BRIGHT; South Pole; South pole
• Online Access: https://curis.ku.dk/portal/da/publications/the-c-iin-ii-ratio-in-3--z--6-submillimetre-galaxies-from-the-south-pole-telescope-survey(e700d4a0-aace-4485-99fa-6659b8f363bb).html; https://doi.org/10.1093/mnras/staa820; https://curis.ku.dk/ws/files/319599343/staa820.pdf

We present Atacama Compact Array and Atacama Pathfinder Experiment observations of the [N II] 205 mu m fine-structure line in 40 sub-millimetre galaxies lying at redshifts z = 3-6, drawn from the 2500 deg(2) South Pole Thlescope survey. This represents the largest uniformly selected sample of high-redshift [N II] 205 mu m measurements to date. 29 sources also have [C II] 158 mu m line observations allowing a characterization of the distribution of the [C II] to [N II] luminosity ratio for the first time at high redshift. The sample exhibits a median L[C II] /L [N II]) approximate to 11.0 and interquartile range of 5.0 -24.7. These ratios are similar to those observed in local (Ultra)luminous infrared galaxies (LIRGs), possibly indicating similarities in their interstellar medium. At the extremes, we find individual sub-millimetre galaxies with L[C II]/L [N II] low enough to suggest a smaller contribution from neutral gas than ionized gas to the [C II] flux and high enough to suggest strongly photon or X-ray region dominated flux. These results highlight a large range in this line luminosity ratio for sub-millimetre galaxies, which may be caused by variations in gas density, the relative abundances of carbon and nitrogen, ionization parameter, metallicity, and a variation in the fractional abundance of ionized and neutral interstellar medium.