Search

We present Atacama Compact Array and Atacama Pathfinder Experiment observations of the [N  ii ] 205 μm fine-structure line in 40 sub-millimetre galaxies lying at redshifts z  = 3–6, drawn from the 2500 deg2 South Pole Telescope survey. This represents the largest uniformly selected sample of high-redshift [N  ii ] 205 μm measurements to date. 29 sources also have [C  ii ] 158 μm 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 |$_{{\rm{[C\,{\small II}]}}}$| / L |$_{{\rm{[N\,{\small II}]}}}$| ≈ 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 |$_{{\rm{[C\,{\small II}]}}}$| / L |$_{{\rm{[N\,{\small II}]}}}$| 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. [ABSTRACT FROM AUTHOR]

We present Atacama Large Millimeter Array [CI](1-0) (rest frequency 492 GHz) observations for a sample of 13 strongly lensed dusty star-forming galaxies (DSFGs) originally discovered at 1.4 mm in a blank-field survey by the South Pole Telescope (SPT). We compare these new data with available [CI] observations from the literature, allowing a study of the interstellar medium (ISM) properties of ∼30 extreme DSFGs spanning a redshift range 2 < z < 5. Using the [C I] line as a tracer of the molecular ISM, we find a mean molecular gas mass for SPT-DSFGs of 6.6 × 1010 M☉. This is in tension with gas masses derived via low-J 12CO and dust masses; bringing the estimates into accordance requires either (a) an elevated CO-to-H2 conversion factor for our sample of αCO ∼ 2.5 and a gas-to-dust ratio ∼200, or (b) an high carbon abundance XCI ∼ 7 × 10-5. Using observations of a range of additional atomic and molecular lines (including [C I], [C II]and multiple transitions of CO), we use a modern photodissociation region code (3D-PDR) to assess the physical conditions (including the density, UV radiation field strength and gas temperature) within the ISM of the DSFGs in our sample. We find that the ISM within our DSFGs is characterized by dense gas permeated by strong UV fields. We note that previous efforts to characterize photodissociation region regions in DSFGs may have significantly under-estimated the density of the ISM. Combined, our analysis suggests that the ISM of extreme dusty starbursts at high redshift consists of dense, carbon-rich gas not directly comparable to the ISM of starbursts in the local Universe. [ABSTRACT FROM AUTHOR]

We present Atacama Large Millimeter Array [CI](1 - 0) (rest frequency 492 GHz) observations for a sample of 13 strongly lensed dusty star-forming galaxies (DSFGs) originally discovered at 1.4 mm in a blank-field survey by the South Pole Telescope (SPT). We compare these new data with available [CI] observations from the literature, allowing a study of the interstellar medium (ISM) properties of ~30 extreme DSFGs spanning a redshift range 2 < z < 5. Using the [C I] line as a tracer of the molecular ISM, we find a mean molecular gas mass for SPT-DSFGs of 6.6 × 1010 M☉. This is in tension with gas masses derived via low-J 12CO and dust masses; bringing the estimates into accordance requires either (a) an elevated CO-to-H2 conversion factor for our sample of αCO ~ 2.5 and a gas-to-dust ratio ~200, or (b) an high carbon abundance XC I ~ 7 × 10-5. Using observations of a range of additional atomic and molecular lines (including [C I], [C II]and multiple transitions of CO), we use a modern photodissociation region code (3D-PDR) to assess the physical conditions (including the density, UV radiation field strength and gas temperature) within the ISM of the DSFGs in our sample. We find that the ISM within our DSFGs is characterized by dense gas permeated by strong UV fields. We note that previous efforts to characterize photodissociation region regions in DSFGs may have significantly under-estimated the density of the ISM. Combined, our analysis suggests that the ISM of extreme dusty starbursts at high redshift consists of dense, carbon-rich gas not directly comparable to the ISM of starbursts in the local Universe. [ABSTRACT FROM AUTHOR]